2. EXISTING PROJECTS, PRIOR STUDIES, AND REPORTS

3. EXISTING AND WITHOUT-PROJECT CONDITIONS

4. PLAN FORMULATION

5. DESCRIPTION OF INITIALLY PROPOSED NER PLAN AND THE PROGRESSIVE NER PLAN

6. PLAN IMPLEMENTATION

7. SUMMARY OF COORDINATION, PUBLIC VIEWS, AND COMMENTS

Table 3.1 - USGS Stream Gaging Records
Table 3.2 - Major Flood Peaks for Composite Record at Wilson, WY
Table 3.3 - Natural and Regulated Discharge- Frequency Relations
Table 3.4 - Partial List of Land Use in Teton County
Table 4.1 - Study Area Problems
Table 4.2 - Study Area Opportunities (Planning Objectives)
Table 4.3 - Site Significance Rankings
Table 4.4 - Restoration Features Comparison
Table 4.5 - Site Comparisons
Table 4.6 - Configurations of Management Measures by Study Area
Table 4.7 - Piling Sizes
Table 4.8 - 16 Alternatives for Detailed Evaluation
Table 4.9 - Cost Estimate for Area 1
Table 4.10 - Cost Estimate for Area 4
Table 4.11 - Cost Estimate for Area 9
Table 4.12 - Cost Estimate for Area 10
Table 4.13 - Aquatic Habitat Trends 1998-2050 Without Project
Table 4.14 - Riparian Habitat Trends 1998-2050 Without Project
Table 4.15 - Aquatic Habitat Units
Table 4.16 - Riparian Habitat Units
Table 4.17 - Aquatic Habitat: Costs and Outputs for All Alternatives
Table 4.18 - Aquatic Habitat: Cost-Effective Combinations
Table 4.19 - Aquatic Habitat: Incremental Cost Analysis (Best-Buys)
Table 4.20 - Riparian Habitat: Costs and Outputs for All Alternatives
Table 4.21 - Riparian Habitat - Cost Effective Combinations
Table 4.22 - Riparian Habitat: Incremental Cost Analysis (Best-Buys)
Table 4.23 - Cross-Comparison of Aquatic and Riparian Costs and Benefits
Table 4.24 - Initially Proposed NER Plan Cost and Output Summary
Table 4.25 - Initially Proposed NER Plan Quantities Refinement
Table 4.26 - Refined O&M Quantities
Table 4.26.A - Initially Proposed NER Plan Refined Cost Estimate Summary
Table 4.26.B - Initially Proposed NER Plan Preliminary Cost Estimate Summary
Table 4.26.C - Change in Cost Estimates Summary
Table 4.27 - Configurations of Management Measures by Study Area: Progressive Plan
Table 4.28 - Construction and Monitoring and Cost Timeline
Table 4.29 - Incremental Analysis: Progressive Plan
Table 4.30 - Progressive Plan Cost and Output Summary (2001 dollars)
Table 4.31 - Summary Analysis: Progressive Plan vs. Without Project
Table 4.32 - Summary Analysis: Progressive Plan vs. Initially Proposed Plan
Table 5.1 - NER Plan Real Estate, Area 1
Table 5.2 - NER Plan Real Estate, Area 4
Table 5.3 - NER Plan Real Estate, Area 9
Table 5.4 - NER Plan Real Estate, Area 10
Table 5.5 - NER Plan Real Estate Costs
Table 6.1 - Basic Cost Apportionment (FY99 Dollars)
Table 7.1 - Participating Agencies in Feasibility Study and Review
Table 7.2 - List of Study Team and Technical Review Team Personnel
Table 7.3 - Review Milestones

Figure 3.1 - Overwintering Habitat, Without Project
Figure 3.2 - Riparian Habitat, Without Protection
Figure 4.1 - Aquatic Incremental Cost Analysis
Figure 4.2 - Riparian Incremental Cost Analysis
Figure 4.3 - Refined Aquatic Incremental Cost Analysis
Figure 4.4 - Refined Riparian Incremental Cost Analysis
Figure 4.5 - Cost Effectiveness of Progressive Plan

Plate 1 - Vicinity Map
Plate 2 - Project Location Map
Plate 3 - Twelve Reconnaissance Sites
Plate 4 - Initial and Progressive Plan Areas
Plate 5 - Existing Levees
Plate 6 - Typical Levee Section
Plate 7 - Teton Fault Block Tilting
Plate 8 - Summary Hydrographs
Plate 9 - Stream Gaging Network
Plate 10 - Average Erosion or Deposition, 1954-1988
Plate 11 - Main Channel Hydrology, 1956
Plate 12 - Snake River Cross Sections, 1956 and 1986
Plate 13 - Main Channel Hydrology, 1986
Plate 14 - Vegetation Cover Types, 1956
Plate 15 - Vegetation Cover Types, 1986
Plate 16 - Area 1 Plan
Plate 17 - Area 4 Plan
Plate 18 - Area 9 Plan
Plate 19 - Area 10 Plan
Plate 20 - Site 9 Existing (1996)
Plate 21 - Site 9 No-Action/Year 2050
Plate 22 - Site 9 With-Project 0-Year
Plate 23 - Site 9 With-Project 5-15-Year Vegetation
Plate 24 - Site 9 With-Project 25-Year Vegetation
Plate 25 - Site 9 With Project 50-Year Vegetation
Plate 26 - Channel Capacity Excavation
Plate 27 - Side-Channel Pool
Plate 28 - Off-Channel Pool
Plate 29 - Spur Dike
Plate 30 - Eco Fence
Plate 31 - Eco Fence with Debris
Plate 32 - Eco Fence with Large Debris
Plate 33 - Rootwad
Plate 34 - Area 4: 100-Year Flood Profiles
Plate 35 - Area 9: 100-Year Flood Profiles
Plate 36 - Area 10: 100-Year Flood Profiles

Appendix A - Feasibility Study Cost Sharing Agreement and Project Study Plan
Appendix B - Hydrology
Appendix C - Ground Water
Appendix D - Engineering
Appendix E - Economic
Appendix F - Real Estate Plan
Appendix G - Cost Estimates
Appendix H - Environmental Assessment

AFB: Alternative Formulation Briefing.

BLM: U.S. Bureau of Land Management.

CAR: Fish and Wildlife Coordination Act Report.

CEQ: Council on Environmental Quality.

CERCLA: Comprehensive Environmental Response, Compensation, and Liability Act, 42 USC 9601-9675.

cfs: cubic feet per second.

Corps: U. S. Army Corps of Engineers.

cy: cubic yards.

DPR/EA: Detailed Project Report and Environmental Assessment.

EA: Environmental Assessment.

EIS: Environmental Impact Statement.

°F: degrees Fahrenheit.

FY: fiscal year.

Feasibility Report: Jackson Hole, Wyoming, Environmental Restoration Feasibility Report.

Feasibility Study: Jackson Hole, Wyoming, Environmental Restoration Feasibility Study.

FIS: Flood Insurance Study.

fine-spotted cutthroat trout: Snake River fine-spotted cutthroat trout (Onchorhynchus clarki bouvieri)

FONSI: Finding of No Significant Impact.

fps: feet per second.

GI: General Investigations.

HEC: U.S. Army Hydrological Engineering Center.

HQUSACE: U.S. Army Corps of Engineers Headquarters.

IDC: Interest During Construction.

Initially Proposed Plan NER Plan (or Initially Proposed Plan): Jackson Hole, Wyoming, Initially Proposed National Ecosystem Restoration Plan (4 sites)

LERRD: lands, easements, rights-of-way, relocations, and disposals.

lf: linear feet.

MCACES: microcomputer-aided cost estimating software.

mm: millimeters.

N/A: not available.

NEPA: National Environmental Policy Act of 1969.

NER: National Ecosystem Restoration.

NWS: U.S. National Weather Service.

O&M: operation and maintenance.

OIP: Other Interested Parities.

OMRR&R: operating, maintaining, replacing, repairing, and rehabilitating.

PC: private contractor.

PCA: project cooperation agreement.

PED: preconstruction, engineering, and design.

PL: Public Law.

P&G: Economic and Environmental Principals and Guidelines for Water and Related Land Resources Implementation Studies by U.S. Water Resources Council, 1983.

P&S: plans and specifications.

Progressive NER Plan (or Progressive Plan): Jackson Hole, Wyoming, National Ecosystem Restoration Progressive Plan (22-mile reach).

RA: Resource Agencies.

REP: real estate plan.

RM: river mile.

S&A: study and analysis.

SHPO: Wyoming State Historic Preservation Office.

TAC: total annual costs.

TPC: Total project cost.

USBR: U.S. Bureau of Reclamation.

USFS: U.S. Forest Service.

USFWS: U.S. Fish and Wildlife Service.

USGS: U.S. Geological Service.

WGFD: Wyoming Game and Fish Department.

WRDA 1986: Water Resources Development Act of 1986, Public Law (PL) 99-662.

WRDA 1990: Water Resources Development Act of 1990.

Walla Walla District: U.S. Army Corps of Engineers, Walla Walla District.

SPONSOR:

Teton County, Wyoming

U.S. ARMY CORPS OF ENGINEERS:

Planning, Programs, and Project Management Division Planning Branch

Engineering Division

Office of Counsel

Operations Division

Real Estate Division

CONTRACTORS:

Tetra Tech, Inc. Infrastructure Group

PRODUCTION ASSISTANCE:

U.S. Army Corps of Engineers, Walla Walla District Information Management Office, Technical Information Processing

TECHNICAL REVIEW TEAM:

Environmental Analysis	Terry Euston, Normandeau Associates
Economic Analysis	Michael Gorecki, Tetra Tech, Inc.
Engineering Analysis	Doug Lantz, Tetra Tech, Inc.
Real Estate	Richard Carlton, Walla Walla District

Background: In 1990, the U.S. Congress authorized the U.S. Army Corps of Engineers (Corps) to conduct the Jackson Hole, Wyoming, Environmental Restoration Feasibility Study (Feasibility Study) through the General Investigations Program. The purpose of the study was to investigate the feasibility of restoring fish and wildlife habitat that was lost as a result of construction, operation, and maintenance of the Jackson Hole Flood Control Project levees completed in 1964.

The study area is located in and along the Snake River near Jackson, Wyoming, in Teton County See plates 1 and 2 in the Jackson Hole, Wyoming, Environmental Restoration Feasibility Report (Feasibility Report) for vicinity and project location maps. The primary local sponsor is Teton County, Wyoming. The study area borders the National Elk Refuge and is in close proximity to Grand Teton and Yellowstone National Parks.

Prior to construction of the levee system, the study area was characterized by a complex system of braided river channels and wooded islands that provided highly diverse and productive habitat for both aquatic and terrestrial species (see plate 14). The levees have contributed significantly to reducing flood damage within the river corridor, but they have also changed the physical character of the river system, resulting in river instability and severe habitat loss and degradation (see plate 15).

Existing and Historic Conditions: An assessment of existing and historic conditions was conducted for the study. Categories of conditions evaluated included hydrology and hydraulics, environmental resources, geology, geomorphology, and socioeconomics. Technical studies identified the major source of problems in the study area to be river channel instability. The main river channel has a tendency to fill and shift. This tendency has been intensified dramatically within the levee system. As the river changes its course, it can impinge on river island habitats, often resulting in complete destruction. With the loss of these island habitats, many species can no longer survive, especially during the area’s harsh winters. Environmental studies confirmed that systematic channel instability has resulted in reduced diversity of species and diminished production of vegetation in area habitats. Without intervention, the remaining habitats in the study area will continue to become gravel bars with a drastic reduction in the diversity of animal and plant species.

Study Objectives: The overall goal of the recommended Jackson Hole Environmental Restoration Project supported by this study is to restore diverse and sustainable aquatic, wetland, riverside, and terrestrial habitats within the study area. Specific objectives are to investigate the feasibility of: (1) restoring river channel stability; (2) protecting remaining diverse habitats; (3) restoring diversity and sustainability to degraded habitats; and (4) restoring degraded habitats for threatened and endangered species.

Study Methods: The study area encompassed 25,000 acres of the floodplain of the Snake River near Jackson, Wyoming. The area was reduced to 12 potential restoration areas, with selection based upon the extent of habitat degradation and the highest probability of successful restoration. These 12 areas were then screened to identify the top 4 priority sites for detailed study; identified as Areas 1, 4, 9, and 10 (see plates 3 and 4 in the Feasibility Report for maps of these locations). Innovative management measures were developed to protect and restore riverside and aquatic habitats at these sites. Based on the information developed through evaluation of a habitat restoration demonstration project, engineering studies, experience from the operation and maintenance of the flood control project, and other studies, management measures were identified for each of the sites to formulate the restoration plan for the entire river corridor.

Evaluation Criteria: Sixteen alternative restoration plans were evaluated based upon the criteria of environmental effectiveness and economic efficiency. Environmental habitat impacts were evaluated using three habitat models; one developed as part of this Feasibility Report for aquatic habitat and two developed by the U.S. Fish and Wildlife Service for riparian habitat. Cost effectiveness and incremental cost analysis identified the plans that were the best investments for producing varying levels of aquatic and riverside habitats.

Restoration Plans: Two restoration plans were determined to be feasible: the Initially Proposed National Ecosystem Restoration (NER) Plan (developed within this study) and a second, more extensive, Progressive NER Plan, that is the result of subsequent management and sponsor review of this study as well as coordinated partnering among regional agencies, interest groups, and the study team.

a. Initially Proposed NER Plan: The Initially Proposed NER Plan involves implementation at study Areas 1, 4, 9, and 10.

The Initially Proposed NER Plan is estimated to create a total of 104,280 aquatic habitat units and 11,460 riparian habitat units over a 50-year period, which compared to the without-project condition is an increase of 22 and 153 percent, respectively. The proposed restoration will improve habitat for multiple threatened and endangered species that depend on healthy and diverse river-related ecosystems. Threatened and endangered species are identified in section 3.1.3.3 of this report.

The Initially Proposed NER Plan is estimated to have a total cost of $26.3 million (FY99 dollars).

b. Progressive NER Plan: The Progressive NER Plan involves restoration of the entire 22-mile reach of the Snake River starting approximately 2 miles downstream of Moose, Wyoming, to Flat Creek at South Park National Elk Feedgrounds. The Progressive Plan provides the greatest opportunity for environmental restoration of all impacted areas of the Snake River below Grand Teton National Park and above the canyon section of the river managed by the U.S. Forest Service.

The Progressive Plan is estimated to create a total of 409,450 aquatic habitat over a 50-year period, which compared to the without-project condition units is an increase of 28 percent. The Progressive Plan will also create an estimated total of 24,425 riparian habitat units over a 50-year period, which compared to the without-project condition is an increase of 137 percent. The proposed Progressive Plan will improve habitat for the threatened and endangered species mentioned in the Initially Proposed NER Plan, but with habitat acreage restored over the entire 22-mile reach of the Snake River. The Progressive Plan provides the opportunity for greater ecosystem influence due to the restoration of highly degraded habitat over a larger geographic area. The expanded restoration effort will provide greater synergistic effect on adjacent habitats landward of the levees. The area to be restored under the Progressive Plan includes all areas between the flood control levees, and the project will not compromise flood protection.

Prior to implementing new measures, all project areas added under the Progressive Plan will require the same degree of analysis as previously performed for the Initially Proposed NER Plan sites, documented in this Feasibility Report. Efficiencies would likely be realized since additional analysis is proposed only in the planning, engineering, and design phases and would not be repeated in another feasibility study. However, the following will be needed: hydraulic studies; fish and wildlife analyses to determine the most appropriate site specific areas to receive the restoration measures; and supplemental National Environmental Policy Act (NEPA) analysis and documentation.

The Progressive Plan will use a phased construction approach, implementing restoration in Areas 1, 4, 9, and 10 before other areas. The Progressive Plan will enable potential local sponsors to restore sections of the river more quickly and efficiently without the cost and time required for additional feasibility studies. Advancements in ecosystem restoration will occur as a result of the Planning, Engineering, and Design Phase applied to the first four sites and lessons learned from phased construction, monitoring, and adaptive management.

The cost per mile of restoration under the Progressive Plan varies along different parts of the river. The total cost of the Progressive Plan is estimated at $52.3 million (FY99 dollars).

Construction Schedule: The Snake River at Jackson, Wyoming is located within a glacial outwash plain as described in the report. Due to the high sediment load, the general steepness of the valley, the high annual variation in the spring snowmelt, along with a limited construction season, the U.S. Army Corps of Engineers, Walla Walla District has determined that an expanded construction schedule is the most prudent approach to construction within this ecosystem. At each of the 12 project sites the majority of the construction would be accomplished in the first year, and continuing construction would be accomplished over the next 2 to 5 years. While in most cases this approach would be considered to be adaptive management or the operation and maintenance responsibilities of the sponsor, the report provides a convincing argument that stabilization of the channel and project features in this highly dynamic system will require continuing construction.

Cost Sharing: The local sponsor, Teton County, has indicated a willingness to pay a percentage (35 percent) of construction costs contingent upon U.S. Congressional authorization of in-kind service credit as part of the 35 percent cost-share obligation. The local sponsor is pursuing legislation to allow such in-kind service credit. A long-term monitoring and maintenance plan has been developed to ensure that the project performs as designed. The plan would expend 1 percent of the project’s first cost on monitoring and up to 3 percent of the project’s first cost on adaptive management. Teton County accepts responsibility for obtaining all lands, easements, rights-of-way, relocations, and disposals as required for project construction, operation, and maintenance of all areas proposed for construction. The sponsor will take over the project as soon as construction is complete.

Environmental Compliance: The Jackson Hole, Wyoming, Environmental Restoration Project Environmental Assessment (EA) was published and distributed for public comment on March 5, 1999. This document included a draft Finding of No Significant Impact (FONSI), a Clean Water Act Section 404(b)(1) Evaluation and Public Notice Number CENWW-PD-EC 99-01, requesting water quality certification from the Wyoming Department of Environmentally Quality. The documentation describes the anticipated effects of implementing the restoration measures in the Initially Proposed NER Plan, for Areas 1, 4, 9, and 10.

The EA used a programmatic approach to consider and describe the effects of implementing a variety of tools or measures in the proposed effort to restore wetland and riparian habitat in the Jackson reach of the Snake River. That is, the Corps identified a set of environmental restoration tools or measures best suited for the conditions occurring throughout the 500-year floodplain. Each measure was generally described and analyzed for environmental effects with limited site-specific examination.

To help calculate values and costs of the project, the environmental restoration measures for the four sites were more specifically positioned and hydraulically analyzed with provisions for the effects of structures and projected vegetation growth. This planning was done to demonstrate optimized environmental benefits and to assure that the restoration would have no adverse impacts on the flood control function of the levees. However, the programmatic method of analysis was used in the EA in anticipation of the unpredictability of the Snake River. Channel bed complexity, high transport of bedload, and sudden channel direction shifts would likely cause modification to our initial site-specific planning.

The programmatic process requires that as measures are implemented at each site, environmental compliance coordination and documentation will be engaged, allowing site-specific and current consideration. This assures prudent environmental compliance on the original four sites and provides a method to add the eight sites proposed in the Progressive Plan. The environmental compliance that was completed on the original four sites will be updated during the Preconstruction, Engineering and Design phase of the project. This requires Endangered Species Act coordination, modification of the Fish and Wildlife Coordination Act Report, additional efforts on National Historical Preservation Act, and Clean Water Act compliance.

Analysis and coordination on the eight additional sites will be completed individually, to meet the staggered construction schedule. A public notice will be printed and distributed; an environmental baseline study will be completed for hazardous, toxic, and radioactive waste; cultural resource compliance will be completed; and necessary coordination required by the Fish and Wildlife Coordination Act, Endangered Species Act, and the Clean Water Act will be accomplished.

Recommendation: Both the Initially Proposed NER Plan and the Progressive NER Plan will restore and protect important fish and wildlife habitats impacted by the Snake River Federal Flood Control Project. Both plans will provide restored habitats for multiple threatened and endangered species. Both plans will enhance diversity of animal and plant species in a geographical area in which fish and wildlife play a large part in regional and national economies. The Progressive Plan would result in greater synergistic restoration impact over a more extensive portion of this outstanding natural environment. Based upon this Jackson Hole, Wyoming, Environmental Restoration Feasibility Report, implementation of the Progressive NER Plan is recommended as the preferred.

Feasibility Report: The following Feasibility Report summarizes the planning process, results, and recommendations for environmental restoration of the Jackson Hole study area. The study examines: existing conditions; prior studies and reports; projected conditions without restoration; plan formulation; the Initially Proposed NER Plan; the Progressive NER Plan; plan implementation and coordination; and public views and comments. Details of technical studies are provided in the following appendixes: Hydrology, Ground Water, Engineering, Economic,Real Estate, Environmental Assessment, and Fish and Wildlife.

FEASIBILITY REPORT

ENVIRONMENTAL ASSESSMENT

1.1 Study Authority

The Jackson Hole Flood Control Project was authorized in the Flood Control Act of 1950, and provided flood protection by levees and revetment along the Snake River in Jackson Hole, Wyoming. The Jackson Hole Flood Control Project was completed in the fall of 1964, and the sponsor was Teton County. Additional levees were added to the system by other agencies and by emergency flood fight operations of the U.S. Army Corps of Engineers (Corps) and Teton County through 1986.

Authority to operate and maintain the Jackson Hole Flood Control Project was granted by Section 840 of the Water Resources Development Act of 1986, Public Law (PL) 99-662 (WRDA 86), to the Secretary of the Army, including additions and modifications constructed by non-Federal sponsors, provided that the local sponsor provides the first $35,000 in any one year (adjusted for inflation). The Corps signed a Local Cooperative Agreement with Teton County in September 1990, after completion of a Decision Document and Environmental Impact Statement (EIS). The Corps assumed operation and maintenance (O&M) responsibility for the levee system on the Snake and Gros Ventre Rivers in Jackson Hole, Wyoming.

The Jackson Hole, Wyoming, River and Wetland Restoration Study was authorized by the U.S. Senate Committee on Environment and Public Works in a Study Resolution of June 12, 1990. The scope of the study was to determine the feasibility of providing environmental restoration to wetland and riparian habitats located between the flood control levees. Teton County, the local sponsor for the proposed environmental restoration project by the Corps, would provide funds in accordance with cost sharing requirements specified in WRDA 86, as amended.

As required by the National Environmental Policy Act of 1969 (NEPA) and subsequent implementing regulations promulgated by the Council on Environmental Quality (CEQ), an Environmental Assessment (EA) was prepared to determine whether the proposed environmental restoration project constitutes a "major Federal action significantly affecting the quality of the human environment" and whether an EIS is required.

1.2 Study Purpose and Scope

The purpose of this Jackson Hole, Wyoming, Environmental Restoration Feasibility Study (Feasibility Study) is to investigate of the feasibility of restoring fish and wildlife habitat that was lost as a result of construction, operation, and maintenance of levees of the Jackson Hole Flood Control Project, including levees constructed by non-Federal interests. The study area is located along the Snake River, near Jackson, Wyoming, in Teton County.

While the levees have contributed significantly toward reducing flood damage potential along the river corridor, over time the levees have significantly changed the physical character of the river system and contributed to the loss of environmental resources. The environmental restoration project supported by this Feasibility Study is needed to prevent further degradation and destruction of environmental resources within the study area and to facilitate recovery of lost aquatic and terrestrial habitat. A restoration project has high potential for restoring fish and wildlife habitat through enhancement and restoration of the aquatic and riparian environment, including wetland and riparian vegetation and in-stream fisheries habitat.

1.2.1 Study Goal

The overall goal of this Feasibility Study is to investigate the feasibility of restoring diverse and sustainable riverine (aquatic, wetland, riparian, and terrestrial) habitats within the study area.

1.2.2 Specific Objectives

Specific study objectives include investigating the feasibility of:

• Restoring channel stability and in-stream habitat values.
• Protecting remaining diverse (wetland/riparian/terrestrial) island habitats.
• Restoring diversity and sustainability to degraded island habitats.
• Restoring degraded habitats for threatened and endangered species.

1.3 Study Area

The original study area defined in the reconnaissance report encompassed 25,000 acres of the 500-year floodplain of the Snake River and its tributaries in the vicinity of Jackson Hole, Wyoming. The study area was limited to the reach between the town of Moose (near the southern boundary of Grand Teton National Park), and the U.S. Highway 26 Bridge over the Snake River about 7 miles south of Jackson. Twelve potential restoration sites (plates 1, 2, and 3) were included in the study area. The June 1999 Draft Feasibility Report examines only four potential restoration sites: Areas 1, 4, 9, and 10, and is limited to the Snake River between the Gros Ventre River confluence and the aforementioned Highway 26 Bridge (plate 4).

The Progressive National Ecosystem Restoration (NER) Plan involves restoration of the entire 22-mile reach of the Snake River starting approximately 2 miles downstream of Moose, Wyoming, to Flat Creek at South Park National Elk Feedgrounds. The Progressive Plan provides the greatest opportunity for environmental restoration of all impacted areas of the Snake River below Grand Teton National Park and above the canyon section of the river managed by the U.S. Forest Service (USFS).

1.4 Study Area Physical Characteristics

Jackson Hole is a valley about 10 miles wide and 35 miles long situated along the Snake River in northeastern Wyoming (see plate 2). It is bounded by the Teton Range on the west, the high plateaus of Yellowstone National Park to the north, and the Gros Ventre Range to the east. Valley elevations range from about 5,900 feet at the Highway 26 bridge over the Snake River to 6,800 feet in the vicinity of Jackson Lake, with an average elevation of about 6,200 feet in the Federal levee project area. Peak elevations rise to over 13,000 feet.

1.4.1 Climate

The climate of the area from Jackson to Moran, Wyoming is typical of high-elevation, Rocky Mountain valleys. During summer months the area has an abundance of sunshine with low humidity and high evaporation during the daytime. The growing season between killing frosts is limited by extreme diurnal fluctuations in temperature and resulting cold nights. Surrounding mountain areas seldom experience a month without freezing temperatures. Thunderstorms are frequent during the summer months, but individual occurrences affect only limited areas. Resultant storm runoff in the Snake River and major tributaries is small in comparison to stream flows resulting from snowmelt.

Climatological records at Jackson show an average annual temperature of 38 degrees Fahrenheit (°F) with period-of-record extremes of minus 52 °F and 101 °F. Temperatures as low as minus 63 °F have been recorded at Moran. Daily minimum temperatures below freezing usually occur at Jackson from early September to mid-June and freezing temperatures have been known to occur in any month of the year. The average frost-free period (growing season) is about 50 days at Jackson.

The Jackson Hole area is affected principally by moist Pacific maritime air masses brought into the region by prevailing westerly winds, and the valley is somewhat within the rain shadow of the Teton Range. Frequently, cool polar or warm continental air masses invade the region, displacing or modifying the effects of the maritime air masses. These latter types are mainly responsible for the valley’s clear weather and low humidity, as well as its diurnal and seasonal temperature extremes. Jackson Hole is located just west of the Continental Divide, and, in addition to storms from the west, the basin can be affected by orographic lifting of air masses from the north and east. During the summer, subtropical air from the southern Rockies can also be a source of moisture for thunderstorms. However, runoff from these storms tends to be highly localized, and Teton County authorities report that storm runoffs do not reach approach damaging levels.

1.4.2 Topography

The topography of the Jackson Hole valley is dominated by depositions of fluvial material by the upper Snake River, by historical and present tectonic uplifting, and by glaciation. The valley floor is presently underlain by deep deposits of alluvial and glacial Quaternary gravels, sands, and debris. Jackson Hole was formed by differential tectonic uplifting of the Teton Range, which has influenced the present position and channel form of the Snake and tributary rivers. Prior to levee construction, the major rivers and tributaries of the Jackson Hole floodplain had cut braided channels through glacial outwash plains. Braided channels result from a combination of high sediment loads, relatively steep channel gradients, and noncohesive banks. Braided channels are subject to frequent avulsion (channel switching) and lateral channel migration. They are very prone to flooding because of their relatively shallow depth when compared to width, and because of their characteristically unstable or noncohesive banks.

1.4.3 Drainage

The headwaters of the Snake River originate in Yellowstone National Park to the north of Jackson Hole. After passing through Jackson Lake, the river enters the Jackson Hole floodplain. Principal upstream tributaries are the Lewis River, Pacific Creek, and Buffalo Fork. The Gros Ventre River is a relatively large tributary, collecting runoff from a little over 25 percent of the total drainage area above the U.S. Geological Survey (USGS) gage site, Snake River below Flat Creek. It enters the Snake River from the east within Federal levee project limits several miles upstream from the Jackson-Wilson Bridge. Fish, Flat, Mosquito, Cottonwood, Taylor, Squaw, and Spring Creeks are among the smaller tributaries that enter the Snake River in the vicinity of the study area. Flat Creek enters the Snake River at the downstream end of the valley just below the Highway 26 Bridge.

The Snake River and its tributaries in the upper Snake River Basin have regular patterns of natural seasonal flow with high flows during the months of May through July, receding flows in August and September, and low flows in the months of October through April. High flows in the late spring and early summer result from melting of the winter-accumulated snowpack, sometimes augmented by rainstorms. Winter flooding due to thawing conditions and rain-on-snow conditions can occur, but rarely result in damaging flows. For the period of record, maximum annual peak discharges have always coincided with the spring snowmelt season. Total annual runoffs for a given area vary with the amounts of precipitation received during the snowpack accumulation and the snowmelt season.

Regulation of water levels by the use of storage space in Jackson Lake reduces the Snake River flow during October through May and early June and augments Snake River natural flows during July, August, and September in order to satisfy downstream irrigation requirements. Further coordination with the U.S. Bureau of Reclamation (USBR) regarding the regulation of Jackson Lake could result in enhanced environmental benefits presented in this Jackson Hole, Wyoming, Environmental Restoration Feasibility Report (Feasibility Report).

2. EXISTING PROJECTS, PRIOR STUDIES, AND REPORTS

2.1 Existing Flood Control Levees

The original design of the Jackson Hole Federal Levee System provided for approximately 23 miles of continuous, revetted levee along the Snake River. The Federal levee project begins 4 miles below the Snake River Bridge near Moose, Wyoming, and ends about 4 miles below the Jackson-Wilson Bridge (plate 5). The Federal levees were completed in 1964. Over the years, many post-project levees, commonly referred to as the "non-Federal levees," were constructed outside the limits of the Federal levee project. Each non-Federal levee was intended to solve problems for localized areas. Various Federal, State, and local agencies, sometimes with private assistance, constructed these levees. The non-Federal levees include a continuous set of levees on the Gros Ventre River downstream of the Grand Teton National Park boundary and a number of discontinuous levees on the Snake River downstream of the Federal project levees. Most of the Snake River non-Federal levees are along a reach that extends 9 miles from the end of the Federal project downstream to the U.S. Highway 26 Bridge. One non-Federal levee (95 Ranch) is located on the left bank just upstream of the Federal levees.

2.1.1 Federal Levees

With the enactment of the WRDA 86, these levees are now part of the Federal levee project, and the U.S. Army Corps of Engineers, Walla Walla District (Walla Walla District) has O&M responsibility for all of the Jackson Hole levees. The Federal/non-Federal terminology is retained in this report because it has been used in the numerous prior Jackson Hole studies and is familiar to local interests. The original Federal levee system extends from river mile (RM) 961.0 to RM 947.6 on the right bank of the Snake River. On the left bank, the levees begin at RM 961.8 and end at RM 947.6, with a break between RM 957.2 and RM 952.8. The break is in the vicinity of the Gros Ventre confluence in a reach with narrow floodplains left of the main channel. Levees were aligned to follow the edge of the main channel with slight setbacks to avoid undercutting the riprap toe trench. The alignments were then smoothed to reduce direct impingement of the river as the main channel meanders between the levees. The distance between the levees is about 1,000 to 1,600 feet, compared to the natural active meander belt width of 1,000 to 4,000 feet. The distance between levees was designed to restrict the river enough during flood flows to reduce debris accumulation and log jams.

The cross-sectional profile of the levee consists of a lower, toed-in, riprapped portion with a 1 vertical on 2 horizontal slope and an upper cobbled portion with a 1 vertical on 4 horizontal slope (see plate 6). The levee was designed to contain floods of 45,000 cubic feet per second (cfs) below the mouth of the Gros Ventre River and 37,000 cfs above the confluence. Three feet of freeboard was added to the computed water-surface profile to arrive at a top-of-levee design height. Above the confluence, the design elevations for the revetments were set at an equivalent flow height, about 4 feet below the computed profile for the standard project design flood. Recent hydraulic analysis has cast doubt on the ability of the present levee to pass the original design flow.

2.1.2 Non-Federal Levees

The Corps constructed many of the non-Federal levees along the Snake and Gros Ventre rivers in Teton County during emergency flood fight operations (see plate 5). These levees supplemented the flood control efforts of Teton County agencies. The U.S. Soil Conservation Service, the Wyoming Department of Transportation, the Wyoming Game and Fish Department (WGFD), and Teton County constructed other levees. Projects constructed under Federal emergency disaster assistance authorities, such as PL 84-99 or PL 93-228, are categorized as non-Federal unless they were constructed as a replacement for a damaged Federal project. Such emergency projects were not necessarily constructed to the design standards imposed on Federal project levees.

Large sections of the non-Federal levees were intended primarily to protect the river bank, while other segments were intended to limit the channel's natural migration. Portions of the levees also act as channel plugs to prevent floodwater from flowing into certain side channels. Riprap protection was included in construction of segments that needed to resist direct impingement and erosion. Subsequently, additional segments were revetted when the main channel shifted closer to the offset levee portions.

2.2 Prior Studies and Reports

The Snake River and tributaries in the vicinity of Jackson, Wyoming, has been the subject of numerous water resource and environmental resources studies. Past efforts of interest to this Feasibility Report have been conducted by the Corps and other Federal, State, and local agencies. These studies have focused on issues ranging from flood protection, geological quarry investigations, environmental assessments, O&M of existing projects, project modifications for improvement of the environment, and fish and wildlife habitat restoration. The following sections describe pertinent prior studies and reports.

2.2.1 Jackson Hole, Wyoming, Flood Damage Reduction and Fish and Wildlife Restoration Reconnaissance Study, June 1993

The Jackson Hole, Wyoming, Flood Damage Reduction and Fish and Wildlife Restoration Reconnaissance Study responded to two authorities: (1) The Jackson Hole River and Wetland Restoration Study, authorized by the U.S. Senate Committee on the Environment and Public Works to "mitigate for fish and wildlife impacts;" and (2) the Snake River in Wyoming, Interim Upper Snake River and Tributaries Study, authorized by the U.S. Senate Committee on Public Works to determine whether modification of the upper Snake River would be advisable.

This Feasibility Report also addresses both authorities in a combined study effort which allows a coherent and consistent formulation of the without-project scenario for the study area. This consistent picture of without-project conditions provides a common base to formulate alternatives addressing both authorized study purposes (i.e., flood damage control, and fish and wildlife restoration). The comprehensive approach better serves the public while increasing overall management efficiency. The combined approach is also consistent with the Position Paper, issued August 14, 1992 by the Walla Walla District, developed with the Corps, North Pacific Division, and approved on October 21,1992 by Corps Headquarters (HQUSACE).

2.2.2 Snake River in Wyoming Interim, Upper Snake River and Tributaries Study (General Investigations)

The Snake River in Wyoming Interim Study was first initiated in 1961 in the Joint Report Upper Snake River Basin, 1961 by the Corps and the USBR. The Interim Report No. 6, Lower Jackson Hole Channel Project was published in April 1965. In this report, the Corps identified improvements to be done in the 8 miles of the Snake River below the Federal levee project and recommended that the levee system be completed to the U.S. Highway 26 Bridge. In August 1986, Teton County requested that the interim study be resumed to evaluate opportunities for reducing flood damage for the whole levee system. A draft Preliminary Report, completed by the Corps in December 1988, recommended that detailed levee modification studies be undertaken. Congressional commitments originally called for submittal of an interim report by November 1988, but this report was delayed while the Corps evaluated the economic feasibility of O&M as mandated by WRDA 86.

The Corps elected to prepare a decision document because insufficient resources were available to complete a feasibility study document. The preliminary study resulted in a draft General Investigations (GI) Decision Document dated June 1990. This document recommended detailed studies for extending the left bank Federal levee above the mouth of the Gros Ventre River and raising the Gros Ventre River levees to the 100-year protection level. The draft GI Decision Document was never finalized because of anticipation of resuming the Snake River in Wyoming Interim Study. The Snake River in Wyoming Interim Study resumed in March 1992 with a scheduled completion date for the feasibility report and EIS in 1993. Under this study, improvements to the levee system were evaluated.

A NEPA scoping meeting was held in Jackson, Wyoming, on March 4, 1992 to elicit comments about the proposed levee improvements from the public. Many local groups urged the Corps to implement a comprehensive planning approach to the entire levee system and to consider the effects that individual projects may have on the rest of the system. The Corps received several letters from individual property owners, local officials, and various organizations. These people stated their concern with a piecemeal evaluation and requested that the EIS for the possible extension of the left bank Federal levee and raising of the Gros Ventre levees consider the whole levee system. This reconnaissance report, which combines all area studies into one comprehensive study, is in response to those requests.

2.2.3 Jackson Hole Restoration Study (General Investigations)

The NEPA review process for the May 1990 O&M EIS resulted in numerous requests for the Corps to mitigate for environmental effects of levee construction. Public input on this subject generally stressed the national significance of the affected resources. As a result, the Jackson Hole Restoration Study was authorized in the Water Resources Development Act of 1990 (WRDA 90) and funded for fiscal year (FY) 91 to determine how levees affected fish and wildlife and to recommend short-term and long-term restoration. The reconnaissance phase study was initiated in March 1991.

The O&M EIS process resulted in a Section 7 Endangered Species Act consultation with the U.S. Fish and Wildlife Service (USFWS) on endangered species (bald eagles). The Corps agreed to use the Restoration Study to evaluate short-term measures for spring creeks improvements that might be implemented under O&M funding. Therefore, the reconnaissance study identified specific short-term recommendations for solutions to implement the Section 7 agreement with the USFWS. The Record of Decision, signed September 1990, requires the Corps to improve the spring creeks to benefit bald eagles. Also, as part of these short-term measures, culverts for fish passage were to be modified in FY 92 as agreed to under Section 7.

2.2.4 Jackson Hole Section 1135 Study (Continuing Authority Program)

Under Section 1135(b) of WRDA 86, a fish and wildlife restoration demonstration project was approved for implementation in the Jackson Hole area. The original legislation provided for implementation of demonstration projects during a 2-year period, beginning November 17, 1986. However, Section 307(d) WRDA 90 added the demonstration program to the Corps Continuing Authority Program, resulting in the removal of funding limitations of the original demonstration project allocation. The initial estimate was for a $480,000 island protection and spring creeks restoration project.

The project proposed for implementation under Section 1135 will provide information on spring creeks restoration design and costs. The Section 1135 study is intended to serve as a prototype for identifying water relationships in the riparian zone between the river, groundwater, and surface waters behind the levee; and how these relationships directly relate to the larger Feasibility Study effort and the potential recommendations.

The draft Detailed Project Report and Environmental Assessment (DPR/EA) was completed in January 1992. The draft DPR/EA proposed protecting a wooded island and restoring flows to some of the alluvial channels cut off by one segment of the levee system in the Jackson Hole area. On April 21, 1992, the island protection was deferred because of concern about downstream impacts that had not yet been evaluated. It was recommended that the island protection proposal be evaluated in a feasibility study that considers system-wide impacts and interrelationships.

2.2.5 Snake River at Spring Creek Section 205 Study (Continuing Authority Program)

Because of local problems of avulsion in the Spring Creek confluence area, Teton County requested a Section 205, small flood control project, study, which was initially approved by the Corps. This study was later deferred until comprehensive solutions (i.e., this Feasibility Study along with the other flood damage reduction solutions at other sites in the area) could be evaluated.

2.2.6 Other Prior Studies and Reports

2.2.6.1 South Park National Elk Feedgrounds Section 205 Study (Corps, 1951)

A Section 205 Detailed Project Report: South Park (Elk) Feedgrounds Location, Snake River, Wyoming, dated September 5, 1951, recommended levee improvements to protect the Elk Feedgrounds. The Corps did not construct a project, but later the WGFD constructed a levee.

2.2.6.2 Upper Snake River Basin Study (Corps, BUREC, 1961)

A joint study of the upper Snake River Basin by the Corps and the USBR was completed in 1961. Corps participation was authorized under the Upper Snake River and Tributaries study authority. This study recommended extending the left bank Federal levee downstream to the U.S. Highway 26 Bridge, and a 0.6-mile section at the lower end of the right bank of the project where the current Evans Levee is located. Parts of the left bank levee were constructed over the years as the Federal Extension, Imenson, Spring Creek, Game and Fish, and South Park Levees. These were non-Federal intermittent levees.

2.2.6.3 Upper Snake River and Tributaries Study Interim Report No. 6 (Corps, 1965)

The Upper Snake River and Tributaries Study, Interim Report No. 6, Lower Jackson Hole Channel Project, Snake River, Wyoming, dated April 1965 recommended construction of levees on the sites of the current Sewell/Taylor Creek Levees and the Imenson Levees. The Sewell Levee was constructed by the Corps for the Soil Conservation Service in 1977, the Lower Taylor Creek Levee was constructed by the Corps in 1969 under Operation Foresight (PL 84-99), and the Imenson Levees were constructed from 1967 to 1971 under flood fight operations.

2.2.6.4 Section 208 Emergency Clearing and Snagging Study (Corps, 1968)

A Section 208 Emergency Clearing and Snagging Project Report, Snake River, Wyoming, RM 955 to RM 965.5, Imenson Location, dated October 4, 1968, recommended clearing and snagging this channel section under the Continuing Authority Program. This work resulted in an unrevetted setback levee referred to as the Upper Imenson.

2.2.6.5 Jackson Hole, Wyoming, Flood Protection Project Letter Report (Corps, 1988)

An unpublished draft Letter Report, completed in January 1988, considered various alternatives for improving the levee system and the studies required to evaluate these alternatives. This study was followed up by the O&M EIS. Limited clearing and snagging was completed in 1989 to remove snags from the river because the snags were adversely affecting the levees.

2.2.6.6 Geological Reconnaissance and Quarry Investigation Reports (Corps, 1989, 1992)

A Geological Reconnaissance and Quarry Investigation Report was completed in April 1989 that located a number of potential quarry sites for riprap to maintain the levees under O&M authority. A second report prepared in December 1992, entitled Jackson Hole, Wyoming, Geologic Investigations of Potential Quarry Sites investigated in greater depth several of the potential quarry sites.

2.2.6.7 Hydrologic and Hydraulic Investigations Report (Corps, 1990)

A Hydrologic and Hydraulics Investigations Report was published in December 1990. The report summarized the hydrological work completed to date on various studies in Jackson Hole. Additional sedimentation analysis information is included in this report as appendix B, Hydrology.

3. EXISTING AND WITHOUT-PROJECT CONDITIONS

3.1 Existing Conditions

An assessment of existing baseline conditions was conducted as part of this Feasibility Study. Subjects evaluated include: Geology and Geomorphology, Hydrology and Hydraulics, Environmental Resources, and the Human Environment. The following pages provide summaries of the existing conditions assessment for each of these categories.

3.1.1 Geology and Geomorphology

Jackson Hole is an intermontane basin bounded on the west by the steeply sloping face of the Teton Mountain Range and on the east by the Gros Ventre Range. This basin was formed when a large block of the Earth's crust raised up along faults to form the Teton Range at the same time that the valley subsided (see plate 7). Movement along the faults began during the formation of the Rocky Mountains approximately 9 million years ago and has continued to the present time. Pleistocene Epoch (approximately 3 million years ago) and recent movement along the Teton Fault, have been the dominant factors determining the positions of the streams on the floor of Jackson Hole, south of Jackson Lake. Large vertical displacements along the Teton and adjacent faults have exposed bedrock, primarily along the valley walls. As a result of Pleistocene glaciation, the valley floor is composed of a thick sequence of glacial sediments.

Large glaciers that advanced and retreated in the vicinity of Jackson Hole during the Pleistocene left behind a landscape abundant in glacial features. The Teton Range was carved by glacial ice, leaving behind high peaks, deep cirques, v-shaped canyons between the peaks, and moraine impounded lakes. The valley was the dumping ground for glacial debris as evidenced by numerous terminal and lateral moraines, not to mention the large blanket of material deposited on the valley floor. The present day stream morphology in the valley is generally referred to as a high energy braided system and is greatly influenced by the large amounts of glacially derived sediment that the streams must transport. The paths that the streams follow in the valley are, however, controlled by tectonic tilting of the bedrock beneath its thick sediment cover.

Downstream from the Gros Ventre confluence, several features suggest that the Snake River channel has been aggrading. These features include flat or convex valley cross sections, low or poorly defined channel banks, a wide meander belt, old channel scars indicating wide-spread shifting of the channel in the past, and tributary streams which turn abruptly on entering the valley and then flow parallel to the Snake River. Another contributing factor, that may possibly be influencing the parallel flow of tributary streams on the west side of the valley, is tectonic tilting of the Teton fault block. The gentle, but measurable, westward slope of the terrace surfaces, and the absence of alluvial fans along the western edge of the valley, suggest that tilting of the valley floor may still be in progress.

Some concern has been expressed that the river, if unrestrained, might suddenly shift westward into the lower Fish Creek Channel, permanently flooding the town of Wilson and sur-rounding developments. However, it could be argued that the river would have escaped its present channel and become permanently trapped against the eastern toe of the Tetons long ago if tilting were the predominant influence. The river has, in fact, overflowed into these areas during past floods. However, any sudden changes in the slope of the valley floor, resulting from earth-quake activity, could result in major changes in the path of the Snake River. The Jackson Hole area is considered to be a highly active region.

3.1.2 Hydrology/Hydraulics

The existing condition assessment for hydrology and hydraulics is summarized below in the following sections: Precipitation, Runoff and Peak Discharges, Water-Surface Profiles, Erosion and Sedimentation, Flooding, Existing Levee System, Jackson Dam Operations, and Groundwater.

3.1.2.1 Precipitation

The average annual precipitation varies from about 16 inches at Jackson to about 60 inches near the summit of the Teton Mountain Range. Minimum and maximum annual precipitation totals vary from about 60 percent to 150 percent of the mean annual precipitation, respectively. The 6-hour maximum rainfall for the 100-year storm is in the range of 2 inches +0.5 inch, and the 24-hour maximum rainfall is in the range of 3 inches +1 inch. Precipitation is rather evenly distributed throughout the year in the valley, but more concentrated at higher elevations in the winter. Due to the cool temperatures of this high-elevation area, the precipitation accumulates mainly as snow from October through May. Average annual snowfall varies from about 80 inches at Jackson to over 300 inches at high mountain snow courses. Maximum annual snow depths vary from about 2 feet to over 10 feet, depending on the location. Maximum depletion rates of snow normally occur during May and June, often resulting in flood conditions on the Snake River.

There are approximately six climatological stations in the Basin with long-term records. Currently, the National Weather Service (NWS) maintains 10 climate stations providing daily readings in the Snake River drainage above Alpine and perhaps a dozen stations providing similar climatic measurements in nearby basins. The Natural Resource Conservation Service maintains seven Sno-Tel stations in the upper Snake River Basin above Palisades Reservoir providing real-time snow water equivalent readings and limited temperature and precipitation information. As with the climatological stations there are numerous additional stations in nearby basins that have good correlation with the Snake River sites. The Natural Resource Conservation Service also coordinates and publishes semimonthly snow course measurements for 17 stations in the Snake River Basin above Palisades. About nine snow courses have long-term records, some of which are used by various agencies in conjunction with precipitation measurements in computing spring runoff forecasts. Representative climatological and snow course information is given in appendix B, Hydrology.

3.1.2.2 Runoff and Peak Discharges

The Snake River and its tributaries in the upper Snake River Basin have regular patterns of natural seasonal flow with high flows during the months of May through July, receding flows in August and September, and low flows in the months of October through April. A summary hydrograph for the USGS gage, Snake River Below Flat Creek, is shown on plate 8. High flows in the late spring and early summer result from melting of the winter-accumulated snowpack, sometimes augmented by rain storms. Winter flooding due to thawing conditions and rain-on-snow conditions can occur, but rarely results in damaging flows. For the period of record, maximum annual peak discharges have always coincided with the spring snowmelt season and sometimes persist for days or weeks. Total annual runoffs for a given area vary with the amounts of precipitation received during the snowpack accumulation and the snowmelt seasons. Summer thunderstorms are common in the mountains. However, runoff from these storms tends to be highly localized, and Teton County authorities report that storm runoffs do not approach damaging levels.

The annual pattern of discharge in the Snake River (and the study reach) is substantially modified by the storage and release of water for irrigation from Jackson Dam, which forms Jackson Lake. Regulation by the use of storage space in the lake reduces the Snake River flow from October through early June. Corresponding to the peak irrigation season, high flows are released into the river from July to September. Sustained flows during the summer sometimes exceed 11,000 cfs, which approximates natural (pre-levee) bankfull discharge conditions. Operation of the Jackson Lake Dam is discussed in greater detail in section 3.1.2.7 of this report.

The primary source for stream flow records is the USGS. Plate 9 depicts the current USGS hydrological reporting network in the upper Snake River Basin, with the study reach called out just downstream of the Gros Ventre River confluence. In addition to the USGS published discharge data at various gage stations, inflow and release data is available from the USBR for the Jackson Dam and Palisades Dam projects. The stations within the vicinity of the project reach are listed in table 3.1.

The USGS gage designated Snake River Near Wilson, Wyoming, was operated for 3 years during the period October 1972 to September 1975. The gage was located near the Jackson-Wilson Bridge at RM 951. Given its location relative to the Federal levee system, the station period of record has been extrapolated through correlation with other nearby gaging locations to cover the entire period 1904 to the present. A correlation for the 1894 historical peak was also determined. Various drainage areas for the Wilson gage have been published over the years. The USGS determined the drainage area to be 2,342 square miles and carried this value in their annual stream flow listings. Based on this value, one can also determine that the Snake River above the Gros Ventre River confluence has a drainage area of about 1,700 square miles. However, the Walla Walla District and other agencies had approximated the drainage area for the Wilson gage at 2,500 square miles prior to the 1970's. Based on the 2,500 square miles value, the Snake River drainage area above the Gros Ventre River confluence was determined as 1,878 square miles.

Due to the convenient location of the Snake River Near Moran USGS gage, both regulated and unregulated annual peak discharges have been determined for this station for the period from 1904 until the Wilson gage was established in 1972. Unregulated (natural) peaks were computed by determining what the flood peaks would have been naturally without flood control operations and irrigation storage at Jackson Lake. For years when the gage was not operated, estimations of regulated peak discharges were made based on the records of nearby USGS gaging stations, and from estimated or gaged spot flow measurements on tributary streams.

The Wilson gage was discontinued in 1975, and a new gage was established about 13 miles downstream at a location below Flat Creek where channel geometry was more stable. Although there are a number of small tributaries entering the Snake River downstream, including Flat Creek, the peak flow data from the new gage location has generally been used, without adjustment, for the Wilson area. In addition to the computed period of record (1904 to present), an estimate of the 1894 flood peak was made for the Wilson location based on correlation with records for the Snake River at Idaho Falls, Idaho, gage location. The 1894 flood was the largest in recent history for streams in the Northwest, disregarding the 1927 flood resulting from the Lower Slide Lake failure.

In summary, the flows in the study area were based on a composite record developed using correlation with other gages from 1904 through 1972, the actual record at Wilson from 1972 through 1975, and the actual record below Flat Creek from 1975 to the present. Between 1904 and 1988, flood discharge exceeding 10,000 cfs occurred 83 times, and discharges exceeding 20,000 cfs have occurred 15 times. Major floods resulting from normal snowmelt are indicated in table 3.2 (estimated annual peak discharges).

The Snake River frequency curves at Wilson, Wyoming were previously analyzed by the Walla Walla District in 1975. The additional data now available has been added to the previous data in computing new curves used for this Feasibility Study. The approach applied to the analyses of the unregulated (natural) discharge frequency curves is similar in both instances. The present analysis is based on 83 years of systematic recording (1904-87) and includes the 1894 historical peak (41,000 cfs). A log Pearson Type III curve was fit to the data using an adopted skew coefficient of -0.2. Only the regulated peak discharge frequencies were recalculated in 1987 for the Snake River study reach above the Gros Ventre confluence. Peak flood discharges for selected recurrence intervals at this and other locations are listed in tabular form on table 3.3.

3.1.2.3 Water-Surface Profiles

Hydraulic modeling of the Snake River in each of the four selected study areas was performed using HEC-2, a computer backwater model developed by the U.S. Army Hydrological Engineering Center (HEC). Most of the proposed channel modifications would fall within the regulatory floodway as delineated by the Federal Emergency Management Agency in their May 4, 1989 Teton County Flood Insurance Study. The area is designated as a no-rise area which means that actions within or adjacent to the floodway should not result in a rise in the regulatory, 100-year floodwater-surface profile.

Mathematical modeling of this river is very difficult. The flow pattern is braided; the channel bed is constantly changing; and the river does not flow in the same channel from year to year. Gravel bars and accumulations of debris can cause local variations in the water surface. At certain levels, a very small change in the trial water surface results in a very large change in the surface area covered by the water. Due to these and other similar problems, a high degree of reliance should not be placed on the results of the mathematical analysis. Discrepancies of up to 2 feet can be expected in some areas, and a difference of up to 4 feet has occasionally been found in areas where major channel changes have occurred or where divided flow exists. Since the river is constantly changing, the modeling results represent, at best, conditions at one point in time.

The model was calibrated to high-water marks, which were observed during the 1997 peak flood. During the 1997 flood, a peak flow of 32,027 cfs was observed at the USGS gage Snake River below Flat Creek. The results of the hydraulic analysis at each alternative site are indicated in appendix B, Hydrology. Considering the aforementioned limitations, the HEC-2 models provided a reasonably good fit to the observed high-water marks and a thus provide a usable base for comparing the effects of proposed alternatives on the flood elevations.

3.1.2.4 Erosion and Sedimentation

Flow velocities in both the main channels and the secondary channels of the Snake River tend to be high, due to the general steepness of the valley. As a result the channel-bed complex is constantly changing. During high flows, avulsion of the main channel into side channels is common. When the flow erodes a gravel bar or the main channel becomes clogged with debris, the flow can shift direction suddenly and unpredictably.

Construction of the Federal and non-Federal levees along the Snake River blocked the lateral spread of the river and reduced the width of the floodplain and the degree of randomness of the braided system. This limited the ability of the channel to migrate and restricted avulsion activity to the area between the levees, concentrating flows in the existing main channels and increasing the frequency of attack on islands and vegetation between the levees. Bedload materials, brought into suspension by the turbulent flow, are more likely to be carried through the system rather than to be carried laterally into the slower secondary channels where they could be redeposited over a wider area of the floodplain.

Historical channel changes and erosion that has occurred in the past, were documented based on available aerial photographs of the area, some dating back to 1944. Photographs were reproduced at the same scale and overlaid to produce a record of the progressive erosion of vegetated islands and shoreline between 1944 and the present (appendix B, Hydrology). Based on the photographs it was also possible to roughly estimate changes in the active meander belt area and channel length. The analysis provided information on erosional trends, level of instability of each area, characteristic overflow routes, and meander magnitude and length. The photographs generally indicate that the vegetated islands have been progressively reduced in size or eliminated altogether between 1945 and the present. In their place, the river has left a broad active channel confined between the levees in which the bedload is constantly reworked. This constant churning has removed the finer material and thus leaves behind a bed that is predominantly in the gravel and cobble classes [2 millimeters (mm) through 256 mm] In parts of the study reach, half the bedload is in the cobble range (64 mm or 2.5 inches and above).

Historical bed elevation changes were determined for a 33-year period (1954-88) based on a series of sediment ranges (surveyed cross sections) established throughout the Federal leveed reach. The ranges were surveyed in 1954, 1967, 1973, and 1988. The vertical change in the thalweg and the average vertical bed change in the bed were determined along a larger reach that includes the study reach. Detailed results are shown in appendix B, Hydrology.

Over the period of measurement, the surveys revealed a pattern in which areas of aggradation and degradation tended to be the opposite in several critical areas such as near the upstream and downstream ends of the levees and upstream of the Jackson-Wilson Bridge and the Gros Ventre confluence. The final 15-year period (1973-88) again exhibited a tendency toward alternate areas of erosion and degradation in a pattern nearly opposite to the previous period. Alternating areas of erosion and deposition are probably characteristic of the random nature of the process in a braided stream. Over-plots of successive range surveys indicate that a considerable amount of material was moved laterally during major channel shifts. A large part of the material eroded at one loop in the river was probably redeposited as a point bar on the inside of the next loop downstream. The average of erosion and deposition from 1954 through 1988 is shown in plate 10.

The net volume of erosion during the 33-year period was heavily influenced by greater erosion in the early years (1954-67) following the completion of the levees. To an unknown extent, material borrowed from the riverbed during levee construction also contributed to the calculated losses. In the periods between 1967 through 1973, and 1973 through 1988, losses tapered off gradually and then dropped off sharply. Measurements from more recent (and more limited) surveys taken in 1996 indicate that considerable sediment movement has occurred since the last complete survey in 1988. In Area 10, for instance, the 1996 survey indicated that more than 400,000 cubic yards of material may have been lost in this area alone since 1988. The flood of 1997, which peaked at the highest flow since 1918, probably moved a considerable amount of gravel and rearranged the channel-bed geometry.

Comparison of post-levee profiles and pre-levee profiles indicates that the greatest erosion has occurred where the levees had the greatest impact on the pre-project flow patterns during flood conditions. For instance, the area of deposition upstream of the Gros Ventre River corresponds to an area where no levees exist on the left side of the river, and levees on the right generally follow the active meander boundary. Downstream of the Gros Ventre, where the heaviest erosion took place, levees crowd the river to the east cutting off about one-half of the active meander belt width.

Determination of the amount of sediment that is transported through the study reach on an average year and during a major flood event would have been useful information. Unfortunately sediment transport and deposition on this reach of the river is very complex and difficult to determine. During a major flood, the flow is spread across a braided channel system that may look more like the teeth of a saw than a typical channel section. Along the same cross section there may be one or more areas of flow concentration where velocities reaching 10 to 12 feet per second (fps). There are secondary currents that may be moving at 3 to 4 fps, and intermediate areas of shallow overflow, where velocities are anywhere from 0.5 to 3 fps. Sediment is likely to be eroded from one bar exposed to a high-velocity current, then be redeposited a short distance downstream where the flow escapes over the side of the channel. Local residents have reported watching the current shift from the levee on one side of the river to the levee on the other in a matter of hours.

As part of this Feasibility Study, attempts were made to estimate the quantity of sediment that could be transported by the river in an average year by first calculating the initial transport capacity, and then running an HEC-6 computer simulation for an extended period of time to determine the equilibrium transport rate. Widely varying values were calculated depending on the formula used and the reach of the river being used as a transport reach. Numerous runs were also made in an attempt to determine the pattern of erosion and deposition with and without the restoration features for a typical year and for a period of 6 years in the future. Although a reasonable pattern was achieved on some trials the model was far too unstable to be considered reliable.

Due to the complexity of the flow patterns and lack of confinement of the flow, it does not appear possible to accurately model the sediment transport of the study reach with a mathematical model. A two-dimensional model would reproduce the instantaneous velocity distribution better. However, due to the channel complexity, and major channel boundary changes, it is unlikely that it would be successful. Although considerable effort was expended on this portion of the study, the results of the mathematical analysis did not appear to be accurate enough to justify the time and space required to include them in this report. Experience obtained by monitoring the proposed project and observing the effect of various restoration measures will likely provide a much better indication of system response than could be obtained with any modeling effort.

3.1.2.5 Flooding

Flood characteristics of the Snake River are typical of a highly braided stream. Due to the high transport of bedload the channel-bed complex is constantly changing. During high flows, avulsion of the main channel into side channels is common. When the flow erodes a gravel bar or the main channel becomes clogged with debris, the flow can shift direction suddenly and unpredictably. Flow velocities in both the main channels and the back channels tend to be high due to the general steepness of the valley. Flood damages include water damage from inundation, loss of land due to bank erosion, and damage to levees due to erosion or undercutting. Before the levees were constructed, flood damages in unleveed reaches began at flows of 5,000 cfs and became significant as flows increased to the 8,000 cfs to 10,000 cfs range. With the current levee system in place, significant damage now begins in the non-Federal reaches with flows in the range of 11,000 cfs. However, bank materials are often so low in resistance that erosion can continue, to some extent, even during low flows.

3.1.2.6 Existing Levee System

A system of levees was established in the lower reaches of the Snake and Gros Ventre Rivers to minimize flooding, confine lateral channel migration, and prevent bank, channel, and floodplain erosion (see plate 5). The Federal project begins 4 miles below the Snake River Bridge near Moose, Wyoming, and ends about 4 miles below the Jackson-Wilson Bridge. Construction began in 1957 and was completed in 1964. Over the years, an array of non-Federal levees were constructed outside of the limits of the Federal project, each to address a separate problem area. Construction was variously accomplished by local, State, and Federal agencies, sometimes with private assistance.

The federally constructed project provides continuous levees on the right bank of the Snake River between RM 961.0 and RM 947.6. On the left bank, the levees begin at RM 961.8 and end at RM 947.6, with a break between RM 957.2 and RM 952.8. The break is in the vicinity of the Gros Ventre confluence in a reach with a narrow floodplain left of the main channel and includes Area 10. The levees act to: restrict lateral channel migration; confine floodwaters to a narrow, but relatively deep cross-sectional area; and reduce channel aggradation by improving movement of sediment load. The levees reduce the typical flooding zone within which channels migrate from 5,000 to 8,000 feet down to 1,000 to 2,000 feet. The levees are typically earthen and gravel fill constructs. The top width is 10 feet, the back slope is 2 to 1, and the front slope is a combination slope with 2 to 1 near the toe and 4 to 1 near the top (see plate 6). The levee toe and the lower part of the front slope are protected by dumped stone up to a given flow level.

Many of the existing levees were constructed in response to perceived threats arising from avulsion of the main channel. As an example, there was great concern in the 1940's and 1950's that the Snake River was tending westward, posing a major threat to the town of Wilson and upstream developments. There has also been continuing concern that the river could eventually capture the lower reaches of Fish and Flat Creeks. Capture of Fish Creek is prevented as long as the Federal levees are adequately maintained. Capture of Flat Creek would harm the elk habitat area, damage spawning channels, and also endanger the Highway 26 Bridge. In the vicinity of the Gros Ventre River confluence, avulsion of both the Snake River and Gros Ventre River main channels is endangering spawning channels in the Three Channel Spring Creek study area. Bank erosion and channel scour was particularly evident following the 1986 flood. Extensive levee repairs were required during and after that flood, and, in addition, Teton County requested assistance for clearing and snagging operations in the main channels of both the Snake and the Gros Ventre Rivers. In response, a Federally funded, low-level clearing and snagging project was completed in the fall of 1989.

The HEC-2 modeling accomplished for previous floodplain studies have indicated that flow velocities, averaged across the channel, during 100-year flood events vary from 2 to 11 feet per second (fps) on the Snake River studied reaches and from 4 to 9 fps on the Gros Ventre River studied reaches. Field observers have noted that local velocities were much higher at points affected by log jams, flow over riffles and rapids, and at levee impingement points. The majority of the damage to the levee sections often appears to occur during the recession from the flow peak. It is likely that high flows, which override the gravel bars and low-flow meander loops, leave the channel bed clogged with debris and gravel. As the water level drops, the flow follows the path of least resistance where it may be directed against undisturbed land along the bankline. The flow may back up on one side of the channel, then flow rapidly down a steep incline toward the opposite side of the channel. These impinging flows can reach very high velocities, undermining trees, damaging or undercutting levee protection, and resulting in high levels of bank erosion in non-leveed reaches.

Velocity profiles taken during the May-June 1974 flood event (discharge of 13,790 cfs) estimated that high intensity impingement flows (of up to 10 fps) affected on the order of 5 to 10 percent of the Federal project levee length. During the 1991 runoff season the Corps Waterways Experiment Station collected water-surface profile data and measured impinging velocities at 8 different locations within the Federal project reach. Flows during this period varied from 14,000 to 16,000 cfs, which correspond to a 2- to 3-year peak flow event. It should be noted that the high velocities resulted from the flow escaping from a high point on one side and then accelerating across the channel to a low point on the other, where it impinged on the levee embankment. Results indicated that depth-averaged velocities could reach 12 fps in the impingement zone near the levees, and point velocities farther out could occasionally reach 16 fps. Velocities of 8 to 10 fps within 2 or 3 feet of the riprap face were very common at im-pingement locations. Scour depths of up to 15 feet below the water surface were measured in some locations.

3.1.2.7 Jackson Dam Operation

Nearly all of the large natural lakes in the area were formed behind the terminal moraines left by prehistoric glaciers. Jackson Lake, located on the Snake River 38 miles upstream from the city of Jackson, is, by far, the largest of these natural bodies of water, with a volume of 847,000 acre-feet, a depth of over 400 feet, and a length of 20 miles. Outwash from the large glacier at the Jackson Lake location, smaller nearby glaciers, and sediment from tributary streams is distributed downstream, forming a steeply sloping valley floor. Variations in vegetation, as seen on aerial photographs downstream of Jackson Dam, clearly show the patterns of a highly-braided flow that probably extended across the entire width of the valley during glacial recession. Similar patterns can still be seen in outwash from receding glaciers in the Columbia Icefield of Canada.

Outflow from Jackson Lake escapes around the eastern side of the terminal moraine at the present location of Jackson Dam. Episodes of meander belt widening and channel down-cutting have left several terrace levels stepping down to the present active channel bed. The channel entrenchment reaches a maximum depth of about 160 feet near Deadman's Bar (about 16 miles downstream of Jackson Lake Dam). The depth of entrenchment decreases and the width of the floodplain increases as one moves farther downstream. Finally, somewhere in the vicinity of the Gros Ventre River, the terraces disappear and the channel emerges on the surface of the valley. Numerous relic channels and secondary branches can be seen in aerial photographs. These often become active during high-flow periods, allowing flood flows to escape the main Snake River channel and fan out across the valley floor.

Reservoir levels at Jackson Lake have been regulated to maintain optimum breeding and nursery conditions for recreational fisheries (e.g., Mackinaw Lake Trout) to the exclusion of native river species downstream. This has usually meant holding the pool elevation constant from October 1, the end of irrigation season and approximately the middle of Mackinaw egg-laying season, until the eggs hatch in the spring. However, recognizing Snake River fine-spotted cutthroat trout (fine-spotted cutthroat trout) as an important resource, fisheries managers have determined that a minimum stream flow of 280 cfs from Jackson Lake is required to support a healthy population of fine-spotted cutthroat trout. The optimum flow is 400 cfs, and flows above 600 cfs should be avoided. To implement this plan, the lake can be drawn down as much as 5 feet after October 1 to maintain stream flows below the dam. There is an attempt to meet the 280 cfs minimum, but no formal minimum release requirement exists. The USBR Operations Manual, dated December 1997, states in part: "If the reservoir was drawn down to the minimum flood control space on October 1 then the release is set to match inflow. If the reservoir was drawn down below the minimum flood control space on October 1 then the release can be set to a minimum of inflow or 280 cfs whichever is less. The release selected will allow the reservoir to either refill to the minimum flood control space gradually over the winter or refill as much as possible up to the minimum flood control space."

Without Jackson Lake Dam, flows would have dipped below 400 cfs in each of the last 87 years and dropped below 280 cfs in 74 of those years. Statistically, stream flows have been less than 400 cfs 21.1 percent of the time and below 280 cfs for 5.5 percent of the time. With Jackson Lake Dam in place, there were 9 years since 1909 with average annual flows less than 1,000 cfs. The lowest year was 1977 with an average annual flow of 660 cfs. If flows above 4,000 cfs are excluded because they occurred during floods and may not have been held by a moderate size dam, then there were 15 years with average annual flows less than 1,000 cfs. Of these, 6 occurred as back-to-back pairs. Again, the lowest average annual flow was 660 cfs in 1977.

During the construction of Palisades Dam in 1956, the Corps negotiated 800,000 acre-feet of nonexclusive flood control storage at the two projects with 25 percent coming from Jackson Lake and 75 percent coming from Palisades Dam. The agreement requires the USBR to make the storage available between March 1 and May 1 each year unless the Corps and the USBR agree in advance that expected spring runoff would be better controlled by a different operation. Although snowmelt forecasting has come a long way, the exact timing and quantity of runoff is still subject to considerable error. The 1997 spring runoff was nearly 50 percent greater than anticipated, forcing both dams into defensive operation and causing severe flooding downstream.

For the current Feasibility Study, a representative sample of flow periods was selected that reflect current operating needs of downstream irrigators as interpreted by the USBR Reservoir Operations Center. Both 1992 and 1994 were classic low-flow years. The 5-year period extending from October 1991 through September 1996 appeared to provide a full range of possibilities including the 2 drought years of 1992 and 1994 as well as an unusually high runoff year in 1996. Assuming reasonable forecasting, volume becomes a more important indicator of low-flow capability than peak flow. Not surprisingly, irrigation demands are higher in low-flow years than in normal years due to dry conditions everywhere else in the basin. The basin runoff volume for 1994 was the sixth lowest flow on record, and followed only 1 year behind 1992, which was the fifth lowest flow on record. Being recent in history and very low, 1994 was chosen as the test case for low-flow discharge. Irrigation demands in 1992 were considered too extreme for the present analysis.

The HEC’s model, HEC-5, Simulation of Flood Control and Conservation Systems, was used to route the flows through Jackson Lake. The following criteria were used for annual flow routing:

• Maintain a minimum flow of 400 cfs below the dam.
• Maintain minimum irrigation flows at Jackson-Wilson Bridge equal to 1994.
• Draw Jackson Lake down to elevation 6,755 by October 10.
• Do not exceed 15,000 cfs at Jackson-Wilson Bridge.
• Repeat the 1994 irrigation demand curve during each year of the simulation.

This analysis indicated that the 400-cfs minimum could be maintained during the winter if irrigation demand was the same each year. In the draught year of 1992 the irrigation demand was considerably higher than normal, resulting in an October 1 pool level that was several feet lower than would normally occur at this time of the year. It was so low that it would not have been possible to refill the reservoir if 400 cfs had been released during the fall and winter months. Based on the analysis to date, it appears that the 400 cfs could be maintained during normal flow years, but that during drought years similar to 1992, this level of release could not be achieved while still meeting the irrigation demands for the following year. It should be emphasized that the USBR operates Jackson Dam. They are in a better position to consider all of the operational constraints, and should be the agency that makes the final determination whether additional winter flow augmentation is possible

3.1.2.8 Groundwater

In addition to surface sources of water, considerable amounts of groundwater drain into the Snake River in Jackson Hole. The porous and unconsolidated alluvial and glacial deposits are the major aquifers in Teton County. Much of the floodplain is close to the level of the river and laced with abandoned or relief channels. Due to the ready exchange of water between the river and the aquifer, channels that have been abandoned or cut off by levees often still contain flowing or standing water. Along the Snake River and its major tributaries the aquifer can supply very large amounts of water. Water tables are often less than 5 feet below the ground surface for a significant portion of the year. Groundwater levels, reflecting the surface runoff patterns, are highest in the spring and early summer and lowest later in the fall and early winter. Local authorities and Walla Walla District construction personnel report that spring-fed water courses will rise in tandem with the snowmelt runoff in the main streams, but the increase in flow is of a much lesser magnitude and does not seem to approach damaging levels.

In the early 1990’s concerns were raised by residents in the west bank area of the Snake River. At that time, there was basically no documentation of groundwater elevations in the area. The Wyoming State Engineers Office and the Teton County Commission initiated the Observation Well System north off Highway 22 and west of the Snake River channel that included 30 wells. Additionally, the Teton County Resource District through a cooperative arrangement with the USGS installed a surface water gaging system. The Wyoming State Engineer’s Office, Surface Water Division installed a more expanded gaging system that monitored additional stream sites as well as irrigation diversions. In 1997, the Wyoming State Engineer’s Office, Ground Water Division, in cooperation with the Teton County Commission installed an additional 12 observation wells south of Highway 22 and west of the Snake River channel. This completed the system as it exists today with the exception of the 8 reference wells located along the east bank of the river, bringing the total number of wells up to 50.

Due to the infancy of the groundwater and surface water monitoring systems, there are no conclusions to be drawn at this point in the study. Appendix C, Groundwater, contains data that has been collected as part of a database that will be completed in the future. As the restoration effort continues, the existing monitoring system will prove to be a valuable tool for tracking what affects (if any) the restoration measures will have on the state of Wyoming water resource.

3.1.3 Environmental Resources

The existing conditions assessment of environmental resources are summarized below in the following sections: Aquatic Ecology, Terrestrial Ecology, and Threatened and Endangered Species.

3.1.3.1 Aquatic Ecology

The Snake River and tributary streams in the study area provide an environment for a wide variety of aquatic species including invertebrates, plants, and fish. Aquatic invertebrates are a major food source for all carnivorous fish in the Snake River and a wide variety including mayflies, true flies, caddisflies and stoneflies are present. Most are herbivores and detrivores although a few are carnivores.

True aquatic plant communities are supported by standing or flowing water year round and are composed of white buttercups (Ranunculus spp.), speedwell, waterweed, pondweed, and watercress. Mat-forming algae are common in shallow stagnant ponds, and liverwort and stonewart species are also common. The cobble-gravel bottom communities are dominated by foxtail, silverberry, willow, timothy, sedge, muhlenbergia, sweet clover, horsetail, and dock. Aquatic plants, particularly algae, supply a major food source to aquatic invertebrates and to primary consumers such as suckers.

The Snake River in much of the study area is designated as a Class 1 or blue-ribbon trout stream by the WGFD. This designation indicates that the river is of national importance as a trout stream and warrants the highest priority for protection. The fine-spotted cutthroat trout is the key aquatic species to be considered in the mitigation study and planning process. Among the many game and nongame fish species present in the region , the indigenous fine-spotted cutthroat trout is economically the most important species, as it is the major game fish captured by fishermen in the Snake River. The fine-spotted cutthroat trout is a self-sustaining (naturally reproducing) subspecies found only in the Snake River drainage from the Palisades Reservoir in Idaho, upstream to the headwaters in Yellowstone National Park. This wild stock maintains its current population by spawning in suitable habitat, regionally known as "spring creeks," without stocking of juvenile or adult fish to the river system. This trout supplies the major sport fishery in the Snake River, from Jackson Lake Dam down to the canyon area of the Snake River above Palisades Reservoir.

Spawning, rearing, and overwintering habitat are considered to be the major limiting factors for fine-spotted cutthroat trout in the study area. Most fine-spotted cutthroat trout spawning occurs during the period from March through June in the spring creeks that enter the river along the study reach. Openings to many of these spring creeks are currently blocked by levees. Little or no spawning habitat exists in the main river for a number of reasons. These include large sediment bedloads and turbidity in the springtime flows (during the spawning period), human induced modifications to the channel, and a cobble substrate that is typically too large for fine-spotted cutthroat trout spawning. Sloughs and side channels are important sources of rearing and overwintering habitat, particularly for young age classes of fine-spotted cutthroat trout.

Other trout species found in this region of the river are less abundant. They include brook, rainbow, brown, and lake trout (which may pass through Jackson Lake Dam), and possibly grayling. Another game species that is apparently abundant but little utilized by fisherman is mountain whitefish. An increased amount of overwintering habitat would also be used by these species. The overall population distribution is not expected to change with features proposed in the Feasibility Report. Construction, maintenance, and long-term effects for these game fish species would be similar to the effects on fine-spotted cutthroat trout.

Nongame fish species present include suckers (an important food source for bald eagles), five species of the minnow family, with Utah suckers and Bonneville redside shiners most abundant, and sculpins. Small fish may be used as prey by fine-spotted cutthroat trout.

Levee construction and other human activities have led to significant decreases in the amount and quality of spawning, rearing, and overwintering habitat for aquatic species. Increases in these resource types will be needed to promote the future viability of the game and nongame fish.

3.1.3.2 Terrestrial Ecology

a. Vegetation. The vegetation in the upper Snake River drainage near Jackson, Wyoming, is typical of the central Rocky Mountain region. Upland vegetation types in the area include sagebrush-grassland, lodgepole pine/Douglas fir, and subalpine fir/Engleman spruce. The sagebrush-grassland type occurs on the glacial outwash plains and terraces above the floodplain. This type is dominated by sagebrush and perennial grasses, e.g., wheatgrasses, fescues, and bluegrasses. Forests dominated by lodgepole pine occur at lower elevations (6,300 to 7,800 feet) along rivers and above the glacial outwash plain. Douglas fir intermixes with lodgepole pine, but is generally dominant only on ridge tops and east-facing slopes. Subalpine fir and Engleman spruce dominate higher elevation (7,800 to 10,000 feet) forests.

The floodplain along the Snake River and its tributaries includes mixed deciduous/coniferous forests and wetlands. Floodplain forest consists of narrow-leaf cottonwood and willow intermixed with Engleman and blue spruce. Wetlands occur where the water table is high enough to support hydrophytic plants, i.e., plant species that grow in water or on a substrate that is at least periodically deficient in oxygen as a result of excessive water content. These include three major types: palustrine shrub-scrub, palustrine emergent, and aquatic bed. The palustrine shrub-scrub wetlands are found primarily on stable gravel bars and dikes and are dominated by willow and mountain alder. Sedges, cattails, and bulrush are the primary species in palustrine emergent wetlands. The dominant species in aquatic bed wetlands depend on bottom substrate. Aquatic beds along shorelines tend to support watercress. Pondweed is common in streams or ponds with silt bottoms and ballhead waterleaf occurs in rocky substrates.

The study area was once characterized by an abundance of diverse riparian vegetative habitats. Wooded islands, transitioning to riparian and wetland communities were a vital component of the highly productive braided-channel riverine environment. Construction of the levee system through most of the study reach has resulted in erosion, degradation, and in many cases destruction of these island habitats.

b. Mammals. The Jackson Hole, Wyoming, area is known for its diverse wildlife in the valley and surrounding mountains. Mammals such as elk, mule deer, moose, bighorn sheep, and American bison are the most prominent wildlife in the Jackson Hole area. Aquatic furbearers, black bear, wolf, coyote, and a variety of small and medium-sized mammals also occur. Big game concerns focus on usage patterns within the region of Jackson Hole. Important winter feeding areas are located near the work area and migration patterns to and from these feeding areas go through the Snake River drainage. The usage patterns include spring-summer-fall range, winter range, winter/year-long range, critical winter range, and critical winter/year-long range. The local mule deer, elk, moose, and bighorn sheep herds represent these types of usage.

Jackson Hole and the surrounding mountains provide about 1,000 square miles of summer range for approximately 15,000 elk. The National Elk Refuge to the northeast provides about 24,000 acres of winter habitat for 10,000 elk. The WGFD classifies this refuge as a crucial winter range, which is defined as one that determines whether the elk population in the area reproduces and maintains itself at or above WGFD target levels. The Jackson Hole area provides migratory habitat for mule deer throughout the year. The upper Snake River drainage provides year-round habitat for about 200 to 300 moose. During the winter, an additional 400 to 500 moose from the surrounding uplands migrate into the river bottom area. Bighorn sheep are present seasonally in all major drainages within the Snake River and Gros Ventre River Basins.

Smaller mammals including shrews and voles are common in riparian areas along the Snake River and its tributaries. Aquatic furbearers such as beaver, mink, and muskrat are commonly seen in streams, ponds, and backwater areas along the Snake River near Jackson, Wyoming. The levees are generally too rocky or exposed to provide habitat for either the beaver or muskrat. Additional species include the river otter and the hoary bat (both of which are considered rare in Wyoming), the silver-haired bat, and the long-eared myotis. The wolverine and lynx, also rare, occur in the region.

c. Birds. The upper Snake River drainage provides habitat for a wide variety of resident and migratory birds, including waterfowl, raptors, and passerines. Approximately 150 different species have been observed, and 119 are documented or expected to breed in the area. The wetlands, ponds, backwater, and tributary creeks in the Snake River floodplain provide habitat for waterfowl and waterbird spring/fall staging, breeding, nesting, brood rearing, and wintering. The most prominent birds include Canada geese, trumpeter swans (a candidate for Federal listing as threatened or endangered), and sandhill cranes. Detailed information on resident populations of these birds is provided in the EA. Dabbling and diving ducks winter on the river between Moose Junction and South Park and between the Jackson-Wilson and South Park Bridges. Winter duck densities frequently average 139 per mile of river and tributary. Other birds known to commonly occur in the Snake River floodplain near the Jackson Hole area include the loggerhead shrike, black-backed woodpecker, killdeer, tree swallow, yellow-headed blackbird, common nighthawk, belted kingfisher, and Wilson's warbler.

d. Raptors. The high numbers of fish and small mammals provide prey for a variety of raptors. The most commonly observed raptors are eagles, falcons, osprey, hawks, and owls. Most nest in trees behind the levees.

e. Amphibians and Reptiles. Relatively little is known about amphibians and reptiles in the Jackson Hole area. Two frog species, the spotted frog, and northern leopard frog, and one toad species, the boreal western toad, considered very rare or rare in Wyoming, have been documented in the vicinity of the proposed restoration project areas. The sagebrush lizard and western terrestrial garter snake are probably two of the most common reptiles in the area. These two species could be present in the existing riparian vegetation within or near the proposed environmental restoration work.

3.1.3.3 Threatened and Endangered Species

Over 30 rare plant species, tracked by the Wyoming Natural Diversity Database, occur in the vicinity of Jackson Hole levees. Only one of these species, Ute-ladies’ tresses (Spiranthes diluvialis), is Federally listed as threatened. Three additional plant species are protected on USFS lands. It is possible that Ute-ladies’tresses may occur within the proposed restoration area between the levees, however, they do not compete well with aggressive emergent wetland vegetation. The USFWS has documented five animal species in the Jackson Hole area that are classified as threatened or endangered. Endangered species observed in this area include the bald eagle (Haliaeetus leucocephalus), whooping crane (Grus americana), and peregrine falcon (Falco peregrinnus). The Jackson Hole area is also within the historical range for the grizzly bear (Ursus arctos horribilis), a threatened species, and gray wolf (Canis lupus), an endangered species.

Since this document was originally drafted, Canadian lynx (Felis canadensis) was listed as threatened. Peregrine falcon was removed from the Threatened and Endangered Species List on August 25, 1999. This removed all protection provided by the Endangered Species Act. The peregrine falcon continues to be protected by the Migratory Bird Treaty Act. The bald eagle has been proposed for de-listing, with a final decision scheduled for July, 2000. The Snake River cutthroat trout (Onchorhynchus clarki bouvieri) and the Yellowstone cutthroat trout (also Onchorhynchus clarki bouvieri) have both been petitioned for listing under the Federal Endangered Species Act. These species will likely be listed within the next two years, influencing the proposed restoration project.

a. Bald Eagle. The upper Snake River drainage provides year-round habitat for bald eagles. Nesting usually occurs between February 1 and August 15. The Snake River population unit, which includes the Snake River in Wyoming, its tributaries, and Jackson Lake, consisted of 24 known breeding pairs in 1982. The Coordination Act Report received from the USFWS stated, "No work activity within 1 mile of any active nests would occur between February 1 and August 15." For this reason, work is only allowed within 1 mile of active nests (current year) between August 16 and January 31. Changes to this work window must have prior approval from the USFWS. Bald eagles are likely to be found in or near the proposed work area most of the year. The chances of the environmental restoration project having any impact on the bald eagle are minimal due to the timing of the active work. There would likely be no direct impacts (mortality, loss of nest, etc.) or long-term population impacts (reduced reproduction, etc.). There may be some minor displacement of foraging or roosting eagles.

b. Peregrine Falcon. Until recently, the peregrine falcon was considered extirpated from Wyoming. A recovery program was begun in 1980. Between 1980 and 1987, 153 peregrine falcons were released to hack sites (the term used for reintroduction sites) in Wyoming, primarily in Yellowstone National Park and in or near the National Elk Refuge. Approximately 80 to 83 percent of the released birds reached independence. The wetlands and streams along the Snake River south of the Jackson-Wilson Bridge support a variety of birds that are prey for peregrine falcons. This area is considered forage habitat for peregrine falcons and three to four adults and sub-adults have been observed in this region between 1982 and 1988. Peregrine falcons are expected to leave the area soon after nesting is complete. The timing of nesting is similar to that of the bald eagle. They could be in the area any time between February and August.

c. Whooping Crane. The whooping crane is one of the rarest birds in North America. Reintroduction efforts at Gray's Lake National Wildlife Refuge in Idaho have resulted in whooping cranes occupying habitat in western Wyoming since 1977. Whooping cranes are occasionally sighted in the Jackson Hole area, primarily along the Gros Ventre River, and do migrate through the area of Jackson Lake during early spring. There is a chance a whooping crane may stop along the river in the Jackson Hole area, especially if sandhill cranes are using the area.

d. Grizzly Bear. The historical range of the grizzly bear once included most of Western North America. Currently, only six areas in the United States, including Yellowstone and Grand Teton National Parks, support self-sustaining grizzly bear populations. The grizzly bear is a resident species to the area, primarily north of the Jackson Hole area, however, current management in Wyoming by WGFD is to discourage grizzly bears from living in areas of human habitation. The last sighting of grizzly bears in the Jackson Hole area was in 1994.

e. Gray Wolf. The gray wolf historically populated all habitats in the Northern Hemisphere except tropical rain forests and deserts. Currently, the largest populations of wolves in the lower 48 states occur in northern Minnesota. Remnant populations are believed to exist in Wyoming, Washington, Idaho, Montana, Michigan, and Wisconsin. In the summer of 1992, a wolf was sighted in Yellowstone National Park, the first documented observation in over 20 years. Wolves have been sighted this year following the elk herds into the Jackson Hole area (WGFD 1998, USFWS 1998). Gray wolves were re-introduced into northwestern Wyoming in 1995 as part of the recovery effort for this species.

f. Canadian Lynx. The Canadian lynx, the only lynx in North America, is a rare forest dwelling cat of northern latitudes. Lynx feed primarily on snowshoe hares, but also will eat small mammals and birds. The range of this species extends from Alaska, throughout much of Canada, to the boreal forests in the northeastern United States, the Great Lakes, the Rocky Mountains, and the Cascade Mountains. Because the lynx is such a rare animal and there are no reliable population estimates for any region, the size of the total population in the contiguous United States is unknown.

In Wyoming, lynx have been protected as nongame with no open season since 1973. It is suspected that a resident population existed historically in Northwestern Wyoming. Lynx presence has been documented historically and currently in western Wyoming "from the Yellowstone area through the Wyoming Range and Wind River Range, and in the Bighorn Mountains."

3.1.4 Human Environment

This section describes the existing conditions in the study area related to population, land use, land ownership, socioeconomics, recreation, cultural resources, transportation, and irrigation.

3.1.4.1 Population

Jackson, Wyoming is the only incorporated town in the Teton County, and provides typical commercial, service, and public facilities, however there are several unincorporated communities and numerous suburban and rural residential neighborhoods in the area. Major employers in the county, varying with the season, include the Jackson Hole Mountain Ski Resort, Grand Teton Lodge Company, St. John’s Hospital, Snow King Resort, Grand Targhee Ski Resort, Grand Teton National Park and the Teton County School District. The 1990 census indicated a population of 4,472 people in the town of Jackson and 11,172 in the county for a total population of 15,644 permanent residents. The official estimated 1997 population is 6,052 in town and 14,200 in the county for a total of 20,252. The seasonal resident population is considerably higher than this value, probably at least double.

3.1.4.2 Land Use

Land use in Teton County is heavily influenced by land ownership patterns. Federal land in the county is used primarily for recreation, wilderness, wildlife management, and forestry. Private land is primarily classified as agricultural, although the use of land for agricultural purposes has diminished over the years. Over the past few decades, land previously classified as agricultural has been converted to residential and other nonagricultural uses. The Federal government is the largest landowner (97 percent) in Teton County.

Private property accounts for approximately 3 percent (75,000 acres) of Teton County. And privately owned lands in the county are concentrated on the valley floor of Jackson Hole south of Grand Teton National Park. Most of the private lands within Jackson Hole have not been intensively developed, although there has been rural-to-urban land conversion over approximately the past 3 decades. Ranching has declined considerably as an economic activity, but much of the former ranch land remains mainly in agricultural or woodland use.

3.1.4.3 Socioeconomics

The Snake River and its tributaries have been an important resource in the economic and social development of the Jackson Hole area. A study of the economic importance of fishing to Jackson Hole is, in effect, a study of two of the states most outstanding resources: (1) the Snake River and its system of associated smaller rivers and creeks, and (2) the fine-spotted cutthroat trout. Fishing activities create demands for goods and services. The Jackson Hole area has become the summer home and vacation home destination for a number of families since 1970. Expenditures by these families in the Jackson Hole area, like tourist expenditures, represent a new demand for goods and services and a flow of new money into the local economy.

Local jobs maintained by the $143,000,000 output related to sports fishing, accounts for about 25 percent of the total employment of Teton County. This is based on statistics furnished by the Jackson Hole Economic Development Council Web site. Local nonfarm sales in 1997 were estimated at $583,000,000 based on sales tax receipts of $35,000,000 in this sector. The sales tax rate of 6 percent would indicate gross sales of $583,000,000. Approximately 18,500 workers generated this $583,000,000 in sales. This allows each worker to generate $31,600 sales per year. If the $143,000,000 sports fishing output and sales is maintained, 4,500 jobs would be enhanced in the area.

3.1.4.4 Recreation

The Snake River in the vicinity of the four project areas principally experiences recreational use from rafting and fishing. Some waterfowl hunting also occurs on the river. Levees along the four project areas are used for a variety of recreational purposes including walking, hiking, jogging, bicycling, cross-country skiing, horseback riding, bird watching, nature viewing, picnicking, and other similar uses. The levees also provide access for direct river use such as fishing and waterfowl hunting.

The majority of recreational use within the study areas occurs in Area 9 near the Jackson-Wilson Bridge which carries Highway 22. Recreational use at this site occurs year-round, with high use continuing into November. South Park National Elk Feedgrounds receives limited public recreational use, most of which occurs during summer as hiking and nature viewing. However recent improvements in pathways near the Elk Feedgrounds have resulted in increases in public recreational use. The southwest levee at Jackson-Wilson Bridge experiences considerable use. The northwest levee gets only limited use while the southeast levee does not get any use. The northeast levee gets a lot of use due to the close proximity of a park. Many private lands along the river carry recreational easements granted to the U.S. Bureau of Land Management (BLM). In general, boating, wading, hiking, picnicking, etc., are allowed while shooting, hunting, open fires, and camping are not allowed on the private land easement areas. In addition, all BLM lands are closed to camping.

Views of the floodplain, by boaters and other recreationists using the Snake River, are generally restricted because of adjacent riverbanks, levees, and vegetation. The primary views along the rivers are of the mountains, particularly the Grand Teton Mountains, which can be viewed beyond the riverbanks and levees in locations where there are openings in the riparian vegetation.

3.1.4.5 Cultural Resources

The area of the proposed environmental restoration project includes floodplain areas between the levees along the Snake River. A Class 2 reconnaissance survey was performed within the generalized environmental restoration project study area for the Initially Proposed NER Plan during the period August 12 to 16, 1996, by the Walla Walla District’s staff archeologist. Record searches were also conducted. No previously unrecorded cultural properties were found during the reconnaissance survey. Record searches identified two previously recorded sites close to two of the proposed environmental restoration project areas, but outside of the levees. Because the previously recorded sites are located outside of the levees, away from where the proposed actions would occur, the Corps determined that the proposed environmental restoration project would have no effect on any previously listed cultural property. The Corps also determined the potential for the occurrence of any unrecorded cultural properties in the areas of impact to be low.

A copy of the Corps’ Survey Report was forwarded to the Wyoming Division of Cultural Resources, State Historic Preservation Office (SHPO), for review and concurrence. In their letter of February 12, 1997, the SHPO responded that no sites meeting the criteria of eligibility for the National Register of Historic Places would be affected by the environmental restoration project. The SHPO recommended the project proceed in accordance with state and Federal laws, subject to the following stipulation: "If any cultural materials are discovered during construction, work in the area should halt immediately and the Corps and SHPO staff must be contacted. Work in the area may not resume until the materials have been evaluated and adequate measures for their protection have been taken."

On June 17, 1999, the revised implementing regulation (36 CFR Part 800) for the National Historic Preservation Act went into effect. The regulation established an updated process that federal agencies are to follow in complying with the requirements of Section 106 of the Act, (i.e., review and comment on federal undertakings). This process requires that the Corps do additional public notice and coordination on the four sites in the Initially Proposed NER Plan.

The additional eight sites proposed in the Progressive Plan will require a field reconnaissance survey, records search, public notification, coordination, and concurrence from the State Historic Preservation Office for Wyoming. Additional work may be required if historic properties are located in the proposed project area. Analysis and coordination on the eight additional sites will be completed individually, to meet the phased construction schedule.

3.1.4.6 Transportation

Several highway routes provide year-round transportation in the vicinity of the proposed environmental restoration project. The primary route used by north and southbound traffic is U.S. Highway 26 (plates 1 through 4). The highway enters the Jackson Hole area from the northeast, continues through the valley and the community of Jackson and exits the valley to the south. Wyoming State Highway 22 starts on the west side of Jackson, crosses the Snake River at the Jackson-Wilson Bridge, and continues west over Teton Pass. Wyoming State Highway 390 extends north from its intersection with State Highway 22 near the Jackson-Wilson Bridge and is a primary route used by north and southbound traffic on the west side of the valley.

3.1.4.7 Irrigation

Numerous irrigation diversions exist off the Snake River and other major tributaries. Diversions can have significant impacts. As an example, during low water years, the total flow is diverted from the Gros Ventre River in late summer and fall, leaving the lower 3 miles down to the Snake River confluence dry, except for a small amount coming from groundwater springs and irrigation return flows.

The irrigation season generally lasts from about May 1 to October 1. There are currently eight active diversions within the Federal levee project area and an additional eight inactive diversions. Some of the diversion headworks serve more than one canal. The headworks are typically concrete with hand operated slide gates. Downstream of the Federal project levees, there is a major diversion behind the Upper Taylor Creek Levee, a major diversion through the Federal Levee Extension, and a minor diversion at the upstream State Game and Fish Levee. The two major diversions are for irrigation, and the minor one provides a dependable supply of water to a downstream spawning channel tributary to Flat Creek. There are no active diversions in the vicinity of the non-Federal levees along the lower reaches of the Gros Ventre River. However, there is a major diversion along the left bank of the Gros Ventre River just upstream of the Grand Teton National Park boundary. There is also a back channel on the right bank of the Gros Ventre River above the non-Federal levee area from which numerous diversions are made, including some into the country club and golf course developments.

Once Jackson Lake is filled by the spring runoff, Jackson Dam passes inflow. Releases above the level of inflow commence when required by those holding irrigation storage rights. In general, elevated flows last all summer and taper off to minimum releases in September or early October.

3.2 Future Without-Project Conditions

Resurveys of established sediment ranges within the Federal levee reach indicated a net loss of about 3 million cubic yards of material from the entire reach between 1954 and 1988. Most of the erosion occurred prior to 1967 during and immediately following levee construction. Since then, the degradation has tapered off as the channel has adjusted to the new regime. Recent sediment range resurveys covered a very limited length of the reach and are thus somewhat inconclusive. The available surveys downstream of the Federal levee system in Areas 1 and 4 are also somewhat inconclusive although there is some evidence of channel thalweg aggradation at some locations. In the future without-project condition it is expected that the channel (average section and thalweg) will continue to degrade overall at a progressively lesser rate in Areas 9 and 10 with possible continued aggradation in Areas 1 and 4.

While the net erosion within the study reach may not be significant, localized changes in the channel bed will continue to dominate the river between the levees. In the future without-project condition, the Snake River will continue to form and plug new low-flow channels and braided systems between the levees. Previously observed patterns, including alternating and fluctuating zones of aggradation and degradation, are expected to continue. The problem of flow impingement on the existing levees and the associated cost of placing additional low-flow armor to protect them will also continue. This work is currently performed by the Corps, which is responsible for maintenance of the Federal levees.

The remaining in-channel islands will continue to be eroded, and the existing habitat will be lost. Any new islands that form between the levees will not be in place long enough to establish permanent aquatic and terrestrial habitat. The latter problem is compounded by the exceptionally coarse bed material, which makes plant establishment difficult.

3.2.1 Future Habitat Trends

Habitat analyses conducted as part of this Feasibility Study showed a future continued trend of riparian habitat destruction within the levees further promoting the shift from a highly diverse and productive ecological system to one where nearly all out-of-channel habitat is primarily gravel from levee to levee. The degradation in riparian habitats has pronounced impacts on both aquatic and terrestrial species. Aquatic habitat analyses conducted in this Feasibility Study showed that without intervention there would be a trend of continued significant habitat degradation, including the reduction of vital rearing and overwintering habitats. Figures 3.1 and 3.2 (below) display the trend of continued aquatic and riparian habitat degradation that was identified by the study’s environmental modeling.

Figure 3.1 Overwintering Habitat
Without Project

Figure 3.2 Riparian Habitat
Without Protection

4. PLAN FORMULATION

4.1 Problem Identification

In the 1950’s, the Snake River near Jackson, Wyoming was a highly braided system with a broad floodplain and numerous vegetated islands (plate 11). Over time, development of the Snake River levee system has created significant changes in physical processes that have resulted in the loss of valued environmental resources. The levees have reduced the cross section of the main channel and have effectively separated it from the floodplain (plate 12). The resulting concentration of flows lead to a deeper, straighter channel (plate 13) with higher velocity flows that have removed progressively larger sediment sizes. The overall cross section and thalweg have lowered and the remaining bed material, which is now mostly gravel and cobbles, is constantly reworked by low and high flows.

This constant shifting of the riverbed between the levees has eliminated the natural braiding of the river and has resulted in a number of negative effects. Foremost, it prevents reestablishment of stable islands with mature vegetative stands and associated riparian and aquatic habitat (see plates 14 and 15). Second, low flows, especially during the recession of the hydrograph, have a tendency to run across the channel and impinge directly onto existing levees. The combinations of impingement, and locally aggrading areas within the riverbed (which locally raise the water-surface elevation) have necessitated construction of additional armor on the river side of the levees. Since the points of impingement can vary from flood to flood, the additional levee protection represents a high maintenance cost that will continue into the future. Finally, flows will continue to attack the few remaining islands as well as unprotected banks. The environmental consequences include a loss of diversity in aquatic, wetland, riparian, and terrestrial habitat as well as reduced value of remaining in-stream, riparian and terrestrial habitats.

4.2 Problems and Opportunities

Section 4.1 provided a general description of water-related environmental resource problems in the study area. The general source of these problems is increased instability of the river channel as a result of flood control improvements that narrowed the historic floodplain. Specific problems that stem from this channel instability include: (1) system inability to establish and maintain sustainable, diverse riverine ecosystem habitats; (2) declining in-stream aquatic habitat (quantity and quality); (3) declining wetland and riparian habitats (quantity and quality); (4) declining habitats (quantity and quality) for sensitive species, including threatened and endangered species. Table 4.1 summarizes the problems focused on in the study.

To solve problems in the study area, they need to be viewed as opportunities. Table 4.2 presents opportunities to address problems and thereby achieve the study goals and objectives.

4.3 Significance of Environmental Resources and Degradation

The significance of the project area and its environmental resources is a function of its geologic location. The alluvial outwash plain provides riparian and aquatic habitat critical for the life cycle requirements of species within the surrounding Yellowstone ecosystem. The following paragraphs describe the significance of environmental resources within the study area.

The greater upper Snake River begins in Yellowstone National Park and flows in a southerly direction into the Franklin D. Roosevelt National Park before entering Jackson Lake. Jackson Lake controls about one-third of the flow that enters the project area. From Jackson Lake, the Snake River enters Grand Teton National Park before entering the project area below Moose, Wyoming. Within the project area, from Moose to the South Park National Elk Feedgrounds, the river flows through mostly private riparian properties. Below the Elk Feedgrounds, the river enters a steeper canyon area that is managed by the USFS. The river then enters Palisades Reservoir at the Wyoming-Idaho boundary. The project area constitutes most of the privately owned lands surrounding the Snake River in the region. Throughout most of the ecosystem, the river and its surrounding areas are publicly owned and managed.

The uppermost section of the Snake River within Yellowstone and Rockefeller National Parks is within a pristine natural ecosystem with little to no man-induced degradation. From Jackson Lake downstream the river remains within a pristine ecosystem with the exception of its flow-regime, which is altered by the operation of Jackson Lake. Within Grand Teton National Park, the Snake River follows a natural meandering, semi-braided pattern to Moose, Wyoming. Below the town of Moose, within the study area, the flood plain widens, the slope of the valley increases, and the river forms a braided system. Below the South Park National Elk Feedgrounds boundary, the geology changes, and the river enters a more confined canyon. The terrestrial ecology of the river above and below the project area is a naturally functioning ecosystem managed by the U.S. Department of Interior and the USFS.

4.3.1 Significance and Degradation of Riparian Habitats

This wider braided section of the Snake River had historically provided some of the most valued riparian habitats within its ecosystem. The riparian habitats were characterized by the braided character of the channels forming a diversity of islands and wetlands and supporting various life forms of vegetation. The natural cycle of flooding and channel shifts resulted in habitats ranging from submerged aquatic riverine, to emergent scrub-shrub, willow-alder habitats to sapling and mature deciduous cottonwood stands. The area provided habitat for five endangered species and a wide diversity of fauna from river otters and waterfowl to bald eagles. One the area’s most important national values was its wintering habitat. During the severe Jackson Hole winters, when temperatures reach minus 20 °F and minus 30 °F and when snow can accumulate to several feet, big game such as elk, mule deer, and especially moose moved into the valley for cover and food. The proposed project area also provides critical wildlife corridors for the movement of mammals between summer and winter ranges.

Due to the need for erosion and evulsion protection within the project area, the Corps constructed the flood control levee system. When the levees were constructed in the early 1950’s through the 1970’s, two distinct impacts occurred. The levees provided flood protection which encouraged the construction of homes, which displaced wildlife habitat. The second significant impact was the concentration of flows and the loss of riparian habitats between the levees. The islands of mature cottonwoods and diverse wetland communities have been replaced by single or double river channels with enlarged barren cobble islands. The wildlife cover, food, and corridor values have been significantly reduced.

4.3.2 Significance and Degradation of Aquatic Habitats

The fisheries value of the Snake River remains in a natural state above the study area within Yellowstone and Rockefeller National Parks. The upstream sections above Jackson Lake within Yellowstone and Grand Teton National Parks are pristine, but the overall productive value is low. Since this area is geologically young, the waters that flow over the bedrock and poorly formed soils contain limited nutrient loads. Below Jackson Lake in Grand Teton National Park, the natural integrity of the system remains intact but is influenced by irrigation flows from Jackson Lake. Below Moose, Wyoming, in the study area, the character of the river channel and its aquatic resources have changed dramatically.

The study area has historically been characterized by richer, older flood plains that contributed increased productivity to the aquatic system. The once braided, multi-channel system with its diverse adjacent habitats has been replaced with a single or double channel and cobbled shoreline. The value of the shoreline and the diversity of the braided river channel has changed significantly. As the leveed reach has become increasingly less diverse, overwintering habitat has become a significant limiting factor for some species. Survival through the harsh low-flow winter months is a critical life cycle requirement. Harsh winter temperatures and low flows limit fine-spotted cutthroat trout survival. During the winter months trout can survive only in pools that provide protection from ice and predators. Winter predators such as bald eagles, river otters, and fish-eating waterfowl can easily prey on the trout within their restricted areas of habitation. Recent studies have shown that mature fine-spotted cutthroat trout move from below Jackson Lake to the project reach to survive the winter. Not only do the mature fish move downstream, but there is also some evidence that fish from the canyon area may move upstream to survive the winter.

4.3.3 Institutional, Public and Technical Significance of Area Resources

The significance of natural resources in the study area is clear. Technical studies have identified the importance of diverse and productive riparian and aquatic habitats for the survival of fish and wildlife through the ecosystem’s harsh winters. Institutional significance of the study area is demonstrated by its endangered and threatened species. Public significance is demonstrated by the strong local support for the proposed project as evidenced by the sponsor’s construction of a demonstration project in the study area. The study’s evaluation of significance is further described in the following section.

4.4 Scoping of Study Area

The area covered by the reconnaissance study included the Snake River and tributaries, and the associated 500-year floodplains in the vicinity of Jackson Hole, Wyoming. The reconnaissance study reach was bounded by Moose, Wyoming, near the southern boundary of Grand Teton National Park, and the U.S. Highway 26 Bridge crossing approximately 7 miles south of Jackson, and had a floodplain area of roughly 25,000 acres. The array of Federal levees constructed in the 1950’s and 1960’s generally reduced the floodplain area to 2,500 acres, or only 10 percent of the original extent. An initial Project Study Plan for the Feasibility Study again involved the entire 500-year floodplain from Moose to South Park Feed Ground. In order to control study costs and make data collection and analysis feasible, the study team reviewed aerial photography and data generated during the reconnaissance study to select 12 sites that provide the best opportunity for restoration from a fluvial geomorphology and wildlife habitat standpoint.

A new Project Study Plan was then developed for the 12 specific sites. The twelve sites are shown in plate 3. The cost of the study was reduced from over $3 million to just under $2 million, a significant reduction, but still out of the range of the sponsor’s fiscal ability. It became apparent that further efforts to reduce cost could not be effective without further reductions in the overall scope of the study. In an effort to reduce the scope, it was decided to determine and describe the overall environmental significance of each site. The overall study area has high national environmental significance as described in the Jackson Hole, Wyoming, Flood Damage Reduction, Fish and Wildlife Habitat Restoration, Reconnaissance Report (June 1993). To formulate a reduced scope, each of the 12 sites was evaluated in regard to its individual significance resulting the identification of 4 sites for detailed evaluation. The screening process is described below.

4.4.1 Significance-Based Preliminary Screening Framework

In 1983, the U.S. Water Resources Council published the Economic and Environmental Principals and Guidelines for Water and Related Land Resources Implementation Studies (P&G). The methodology in P&G is the analytical procedure currently used by the Corps in evaluating alternative water resources projects. To be considered in plan formulation and evaluation, P&G requires that environmental resources be "significant." Significant environmental resources are defined as those that are institutionally, publicly, or technically recognized as important. As defined in P&G, the term of significant means "likely to have a material bearing on the decision-making process." In terms of environmental plan formulation and evaluation, the significance of environmental resources based on their nonmonetary values may be established by institutional, public, or technical recognition of the importance of the environmental resources or attributes in the study area.

a. Institutional Recognition. The study areas are institutionally recognized by several national laws and regulations. Part of the original area in the reconnaissance study was within Grand Teton National Park with the remainder immediately downstream and adjacent. The southern most section of the study area is adjacent to South Park National Elk Feedgrounds (a state preserve for wintering elk). Within the project area are six bald eagle nesting territories and habitat for five other nationally recognized endangered species. Over 50 percent of the project is classified as wetlands. The scarcity of structural and biological resources which directly support institutional resources was addressed in this study.

b. Public Recognition. As indicated in the project support section of this document, the study area receives significant interest from local and regional environmental groups. The study area is also used by sportsman and recreationists from across the United States. The area, located between a national park and national forest, has considerable recreational value. The fine-spotted cutthroat trout is an endemic wild fishery that provides an $11 million fishery to the county. The study has the potential to improve its value.

c. Technical Recognition. Spring creeks are relatively small streams fed by groundwater discharges of clean, clear water of relatively uniform annual temperature. They provide the critical spawning habitat for fine-spotted cutthroat trout, which in turn provide a forage base for bald eagles. All eagle nesting habitats in the project area are associated with spring creeks.

All 12 sites were ranked individually based on their institutional, public, and technical recognition. Significance rankings are listed in table 4.3.

4.4.2 Multi-Objective Analysis for Site Selection

To further refine the scoping effort, a multi-objective approach was developed. Objectives developed with public input during the reconnaissance phase and refined at the Reconnaissance Review Conference were used in a matrix analysis. The study objectives were defined as: wetland restoration--riverine and palustrine; riparian restoration--island protection and restoration; and endangered species habitat protection and creation.

A multi-objective analysis was conducted using the following objectives:

• Channel Creation. Channel creation to restore fisheries--wetland values dependent on surplus gravel and disposal options (i.e., users of gravel).
• Island Protection. Island protection measures to preserve riparian island values.
• Island Restoration. Island restoration measures to restore lost riparian values.
• Fish Habitat Creation. Fish habitat creation (low energy areas in high energy environments) through stream structure alteration (i.e., spur dikes).
• Headgate Opportunities. Headgate opportunities to provide for future water diversions to restore spring creeks and wetland-riparian habitats.

The ratings for each of these objectives for each project area are listed in table 4.4.

The values relating to overall national significance and environmental engineering feasibility were integrated, and the multi-objective analysis was given a 1.5 weight to select the four sites that provide the best overall opportunity for success. The multi-objective approach was given additional weight because the sites providing the most opportunity provided a synergistic effect and the greatest overall opportunity. Six sites provided similar opportunity. Three sites on the downstream reach had very similar ratings and opportunities for restoration. The study team decided to allow the scoping process with local input and specific knowledge of property ownership and cultural concerns to select the best site of the three downstream sites of equal value. The four sites selected are one of either Area 1, 2, or 3 (Area 1 was selected) and Areas 4, 9, and 10.

4.4.3 Preliminary Screening Results

Thus, the Feasibility Report focuses on four proposed restoration alternative sites referred to as Areas 1, 4, 9, and 10. The four sites are shown on plate 4. The sites are all located within the Snake River in a reach extending from a point 3 miles above the Highway 26 Bridge on the downstream end, to the Gros Ventre River confluence on the upstream end. In the vicinity of the project reach, the right (west) bank Federal levee is continuous from RM 947.6 (near Area 4) to beyond the Gros Ventre River confluence. The (east) bank Federal levee extends from RM 947.6 (near Area 4) to a point roughly 1.7 miles upstream of the Jackson-Wilson Bridge on Highway 22. The remaining 2.5 miles of bank (4.4 river miles) are currently unleveed.

4.5 Formulation of Alternatives

At each of the four study areas, different restoration features were combined into alternative restoration plans for each site. This section describes the restoration measures that were considered and provides a summary of the different configurations of measures at each of the study areas.

4.5.1 Restoration Measures

Restoration measures consist primarily of: construction of eco-fences; excess gravel removal; placement of logs and root wads designed to protect and reestablish wetland and riparian habitats and; creation of side channel backwater areas and off-channel pools. (See plates 29 through 33.) The eco-fences will be placed at the front and sides of existing wooded islands to protect an existing resource or in areas where riparian vegetation has been lost in an attempt to regain the lost soil and vegetation. Generally, attempts to regain vegetation area had been limited to that which existed prior to 1973 in order to avoid reducing the level of flood protection that existed at that time. The purpose of the fence structures is to block, slow down, or deflect the force of the current during high-flow periods in order to protect existing vegetation and allow new vegetation to become established. Fences have been used effectively in low velocity regimes in a number of other instances. Their long-term effectiveness in the high-velocity regime that exists in the area covered by this study remains to be demonstrated.

Gravel and cobbles will probably accumulate to some extent with any reduction in the flow velocity, but flows must be reduced well below 2 fps if a layer of soil is to be reestablished. Willows, and other vegetation which grow in the gravel bed will assist in reducing velocities and encouraging the deposition of silt if they can be protected from direct attack long enough to become established. As vegetation becomes established it further slows flow velocities and encourages accelerated sedimentation.

If a fence fails to perform satisfactorily, it is possible to add more cross cables or wire mesh to increase the trapping efficiency of the structure. A few seasons of operation may be required to measure the effectiveness of the fences and to adjust the existing fence designs for optimum performance. If the fences operate successfully, debris will be swept by the eddy current into the space between each fence, and a raft of logs, limbs, and other flotsam will collect upstream of the fences and form the matrix through which willows and other vegetation will become established. Sand and gravel will collect in the triangular, protected zone downstream of each fence. As vegetation becomes established it will further resist the flow and encourage the accumulation of a new layer of silt, which will support progressively larger varieties of vegetation.

In most cases, the fences will have very little effect on overall river conveyance since they are generally located where conveyance is reduced (i.e., near the banks of existing islands), or where the river has ample room to cut a channel around the protected area. At other locations the fences protect and maintain existing stands of timber, which presently block most of the flow through the affected area. Proposed fences, which encroach on open areas, will nearly always be located where heavy stands of mature vegetation and soil once existed (but were removed by flood flows) and at the site of previously blocked most flood flows.

Gravel removal is designed to accomplish several objectives. In some areas gravel will need to be removed initially in order to increase the capacity of the stream and offset the loss of conveyance resulting from the eco-fences. The stream would naturally enlarge the channel and regain its conveyance with time, but a flood coming in the season following the completion of the fence might raise the water a small, but unacceptable amount above the regulatory flood level. Oversize gravel (the +4 inch material, which generally constitutes from 5 to 20 percent of the mixed gravels in the bed) will be retained and returned to the channel bed and the upstream ends of adjacent islands. This large material is more resistant to movement and actually forms a protective armor layer when flow velocities are below the critical shear stress for the available sizes.

A second function of gravel removal is to reduce the supply of gravel to an area that is overloaded. This, if combined with measures that increase gravel bar stabilization, will result in channel entrenchment and a reduction in the rate and frequency of lateral movement. A third function is to take the pressure off of an eroding bank by opening up existing secondary channels and shifting some of the flow back toward the center of the meander belt. Eco-fences and anchored debris are designed to encourage vegetation growth and help to stabilize the channel pattern. The level of success in maintaining an alignment will probably vary widely with the location and degree of bank stabilization accompanying the gravel removal.

The above objectives could be achieved with reasonable confidence in a meandering channel with a low sediment load. However, the Snake River carries a heavy bedload and is very unstable and braided. It is very difficult to determine how much sediment is being transported, where sediment will be deposited next, or where the channel will be after the next flood. By its very nature, the river is unpredictable and may not respond as desired in some areas.

Changes in sediment transport and river hydraulics, resulting from the implementation of various restoration measures, have been considered in the planning of the project, and will be monitored in order to make adaptive management modification improvements at future phased construction sites. In the remainder of the report the term "improved channel" is sometimes used interchangeably with the term "restored channel" to refer to the modified condition after restoration measures have been implemented in an area.

The grain sizes of materials on the surface in the study areas vary considerably from silt to cobbles 5 to 10 inches in mean diameter. The size depends to a great degree on the velocity of flow at the particular location. However, a foot or more below the surface the material is more uniformly distributed with very little silt and generally less than 15 percent larger than 4 inches. When the river is returned to flow over an excavated area there will be an initial increase in turbidity as the flow picks up the fine material from the surface. This should be of very short duration, perhaps a few hours. Later on, as the flow increases during winter floods or the spring runoff period, the bed will be reworked, and one of several processes will dominate. Fine material in the bed will be entrained and put into suspension. Then, depending on the sediment supply from upstream, more sediment will be deposited than is entrained; an equilibrium will be established between entrainment and deposition; or, if there is a deficient supply, erosion of the bed will occur until enough the large material remains to form a new continuous layer over the bed which will protect the underlaying material from further erosion.

Cobbles which form the new armor layer would come from material transported into the site from upstream, oversize material physically returned to the bed during gravel-removal operations, and material existing in the bed. In the extreme case, with a deficiency of supply from upstream, and no return of cobbles to the bed, the channel bed could degrade to a depth of 2 to 10 feet depending on the amount of large sized material in the bed. Restoring the +4 inch material will significantly reduce the depth of degradation from an average runoff event, since this material will be redistributed over the surface by the current to form a new armor layer. In some areas root wads or logs will be anchored. The root wads are designed to accomplish some of the same objectives as the eco-fences. They will have less of a visual impact and should spread the effect over a larger area. In areas of low velocity sand and silt will collect downstream of the debris and encourage the establishment of vegetation. In higher velocity areas, a sufficient number of root wads will tend to slow the velocity and deflect most of the current around the area to be protected. In some areas, when exposed to the main current the root wads will actually increase erosion by flailing around on the restraints and stirring up the gravel. In these areas, holes, several feet in depth, will be eroded in the channel where each root wad is anchored.

4.5.2 Design Criteria for Restoration Measures

For purposes of comparing the costs and benefits of different levels of protection, it was necessary to select criteria for design and assign a probability of success to various elements of the design. Since there was virtually no historic data of a type that could be used for a rigorous probability analysis for this type of project, probabilities were primarily based on experience and judgment.

The maximum design life of 50 years seemed to be a reasonable value, since woody vegetation will reach a mature level during that time. It also corresponded roughly to the period of aerial photographic data documenting changes in the channel and surrounding vegetation. During the past 50 years, virtually all of the vegetated islands within the meander belt were destroyed at one time or another by the changing channel patterns. In order to provide a comparison, shorter design periods that actually represent intermediate levels of reliability in the selection of structural elements and restoration measures were selected.

From the frequency curves shown in appendix B, Hydrology, it can be seen the peak annual discharges for average return intervals of 15, 25, and 50 years are 22,500, 24,000, and 26,500 cfs. Obviously there is not enough difference in these flows to serve as a criteria for design of structures whose probability of failure is related more to attack by impinging flows, impact by floating debris, and changes in channel alignment, than by a specific flood frequency. For this reason it was decided that a design based on attack by floating debris under three different impinging flow velocities along with the traditional static hydraulic loading, would be a more reasonable approach. Impinging flow, for purposes of this analysis was defined as flow that had a much greater attack velocity due to a local steepening of the upstream channel. The design impingement velocities were based on expected levels of attack. Velocities of 4 fps or greater could be expected when the structures were exposed to high flows even without impingement conditions. For this reason structures should not be designed for anything less than 4 fps. Impinging velocities of 8 fps were frequently seen in the data, and 12 fps occasionally appeared in the data. These velocities were used as a basis for the development of four separate fence designs.

Structures designed for 4 fps would suffer substantial damage if exposed to direct attack by an typical impinging flow. The probability of being exposed to this type of flow may range from 5 to 10 percent each year based on a rough estimate of the length of levee exposed to impinging flows. If 7 percent of the structures were substantially damaged each year, this would roughly correspond to a 15-year life for structures designed for 4 fps. Structures designed for 8 fps would be more likely to survive some impinging attack, perhaps providing a 25-year average life. However, with the present design, the structures would not provide enough continuity to restrict the channel to a fixed alignment.

The braided channels will eventually bypass even the strongest structures, attack the vegetated islands from an unprotected angle and eventually render many of the structures useless. It does not seem reasonable, based on the past erosional history of the river, to assign a project life greater than 50 years. Vegetative growth was based on the assumption that over the entire project the average, effective life of the fences would correspond to the selected intervals. On an average, substantial reconstruction of the entire project would be required at the indicated intervals.

In some areas the restoration measures may be very successful, in others there is likely to be extensive failures. By analyzing past erosion trends and channel patterns, an attempt has been made to maximize the probability that most of the measures will be located in areas where they will meet with an acceptable level of success.

4.6 Description of Restoration Alternatives at the Four Project Areas

This section provides a description of the management measures that make up each of 4 alternatives at each of the 4 study sites for a total of 16 alternatives. Area 1 is described first, followed by Areas 4, 9, and 10.

4.6.1 Proposed Restoration Measures for Area 1

This section provides a site description for Area 1 and identifies specific proposed restoration measures.

4.6.1.1 Area 1 Description

Area 1 encompasses a long sweeping bend in the Snake River and its associated overflow channels and wooded riparian zone (see plates 4 and 16). It is located about 3 miles upstream of the Highway 26 Bridge, starting at the confluence of Spring Creek and extending upstream about 2 miles. The Snake River enters the area flowing generally south, then swings nearly 90 degrees to the east as it comes up against the Snake River Range which blocks its southward path along the lower one-third of this area. The river and its adjacent wooded riparian zone spreads out to a width of about one mile around the bend, but narrows to 2,000 feet or less where the braided channels converge at the lower end. At present the river generally flows around the outer edge of the riparian zone. During high-flow periods, the river overflows into a network of smaller channels that cut across the bend and empty back into the Snake River along the lower half of the bend. During low-flow periods the upper ends of these channels may be dry, but progressing downstream, water seeping in from the shallow aquifer keeps the larger branches flowing during the entire summer.

The channel is highly braided, with 2- to 5-degree braiding over most of its length. The adjacent floodplain is wide and flat. During high-flow periods the channel boundaries are poorly defined and constantly changing. Gravel may completely fill the channel at some locations causing the flow to fan out over a wide area.

A review of historic aerial photographs indicates that the active channel has frequently changed course and pattern. A USGS quad sheet, based on surveys taken 1927-31, indicated that the channel at that time was more centrally located within the meander belt and divided into three main branches. Both of the east branches emptied into Spring Creek, which joins the Snake River at the downstream end of the bend. By 1945 it appeared that the central branch of the channel was being abandoned, but a large channel still cut across to Spring Creek. Over the years the channel moved westward, progressively eroding a 1,000-foot wide wooded riparian zone and cutting into developed pasture lands to the west. In the process the river almost completely abandoned the branch into Spring Creek. Sheet flow still covers the interior gravel bars during spring floods, but willows are springing up, and sand and silt is building up on large expanses which were formerly bare cobbles.

The date for the most recent westward channel movement is not known. There was some westward erosion evident in 1956. A couple of loops were cut into the zone between 1960 and 1962. Large areas of vegetation were washed away between 1967 and 1971, between 1974 and 1981, in 1986, and between 1992 and 1996.

Near the downstream end of Area 1 a large portion of the Snake River formerly flowed into and along the present course of Spring Creek and then flowed back into the main channel from the left. The momentum of the lateral flow and sediment replenishment from this branch of the Snake River probably tended to keep the channel pushed up against the hills to the south. A groin, located just above the confluence on the left side, can be seen in 1953 aerial photos, but appears to be partially or completely destroyed in 1956 photos. Since 1962 the river has progressively cut away slices of the left bank. By 1996 the river had cut nearly 800 feet into riparian land near the mouth of Spring Creek.

Several factors suggest that the river is either moving large volumes of gravel with no net loss; or the area is aggrading:

• The riverbanks are poorly defined or nonexistent.
• The river is invading new areas beyond the meander belt.
• The meander belt is 3 to 4 times as wide as the active channel.
• During peak flow conditions, flow is often shallow and spread out over mid-channel islands which appear to include most of the channel cross section.
• There is an absence of recent terrace formation or other evidence of channel entrenchment.

The low-flow channel exhibited a wide variation of patterns over the years. During some years, such as in 1996, a definite, repeated pattern of fairly uniform meander loops could be seen within the overall braided pattern. In 1945 there was little, if any, regular meandering pattern identifiable within the overall braiding. The 1996 pattern appeared to be more typical of identifiable patterns during the 1945-97 period.

4.6.1.2 Area 1 Restoration Measures

a. Channel Alignment. The natural channel pattern will be retained and allowed to develop to the extent possible. However, several existing channels will be enlarged, as indicated on plate 16, to shift some of the flow back toward the center of the meander belt, take some of the erosive pressure off of the right bank, and allow reestablishment of a riparian zone in this area.

b. Removal of Excess Gravel. A gravel-removal zone, designed to match a typical second-degree braiding pattern, was selected at the upstream end of Area 1. Removal of excess gravel at this location will reduce the supply downstream, encouraging moderate entrenchment of the downstream channels and reducing the frequency and extent of lateral movement. Cobbles over 4 inches in mean diameter will be retained to form an armor layer on the bed and banks of the channel.

The Area 1 gravel removal site was chosen for the following reasons:

• The location allows easy access along the west side from the Taylor Creek Levees or the nearby county road.
• The location will reduce the supply of gravel entering the site while minimizing the area that will be disturbed while excavation is in progress.

During hydraulic modeling of the channel modifications described above, it was found that the eco-fences resulted in a calculated rise in the water level upstream. To offset the effect of the fences, additional excavation is proposed along several existing, secondary channel alignments. This excavation should take some pressure off of the right bank by shifting a majority of the flow back toward the center of the meander belt. The channel modifications will shorten the effective length of the channel and increase the channel conveyance. The sediment supply will be reduced by the upstream sediment trap. If successful, these modifications should maintain adequate conveyance through this reach in the future with little or no maintenance. After completion of the project, the area should be monitored by periodic resurveys of sediment ranges to assure that the amount of sediment removed from the sediment trap does not result in excessive channel entrenchment downstream.

c. Pool and Channel Restoration. Two existing channels were identified and selected for restoration measures. Four pool sites were selected along these channels. The selected sites provide varying degrees of exposure to erosion and sediment inflow. The two pools farthest from the main channel will collect finer sediment and should survive the longest. Connecting channels and associated pools will create flow and depth diversity. Root wads and other in-water debris will provide shade and shelter for fish and other aquatic life.

d. Eco-Fences. Eco-fences and root wad fields along the west bank of the channel are designed to collect sediment, and encourage woody vegetation growth. The objective is to stop westward channel movement and recover most of the riparian habitat lost since 1973. The proposed locations for eco-fences cover areas formerly occupied by mature riparian vegetation, which has been destroyed since 1973. Eco-fences on the left side of the channel are designed to protect large stands of mature cottonwoods should the river shift back eastward across the meander belt. As experience is gained, it may be necessary to make some adjustments or modifications to the fences in order to improve their debris-trapping efficiency or to control erosive velocities between the fences. The modifications might consist of the addition of fence spurs connected to the existing fences or the placement of additional fences or fence panels between the existing fences.

4.6.2 Proposed Restoration Measures for Area 4

4.6.2.1 Area 4 Description

Area 4 covers a braided reach of the river starting at the downstream end of the Federal levee project and extending downstream a distance of 1.6 miles. Fish Creek, Mosquito Creek, and Cottonwood Creek enter the Snake River from the right (see plates 4 and 17). The Upper Imenson Levee forms a boundary to the left. Prior to construction of the Federal levee project the river often followed an alternate course well to the right of the existing levees, with a significant flow following the present course of Fish Creek. During high-flow periods some of the flow escaped into spring creeks which branched off of the main channel in the riparian zone to the left. Levees and levee extensions now cut off most of the overflow into these channels.

Historic aerial photographs indicate that the river was rather unstable in this area. Flows followed alternate paths through the area, sometimes spreading out over a fairly wide expanse, and at other times cutting a single narrow channel through the reach. A characteristic, low-flow meander pattern did not appear to be present in this location. The active meander belt has experienced considerable lateral expansion between 1954 and the present. Large areas were eroded in 1973, and again in the 1986-97 period. Between 1945 and 1954 the active, vegetation-free zone of the channel occupied an average width of about 1,000 feet. In 1977 floodwaters spread out to a width of 2,400 feet with very little vegetation left in between. The location and method used in previous cross section surveys do not provide a sufficiently accurate basis for analyzing gravel erosion or deposition in this area. However, several factors strongly suggest that gravel is building up again in this area:

• The levees immediately upstream of the study area have severely restricted the opportunity for flood flows to spread out and flow into alternate channels. Gravel transport and deposition is now restricted in the area between the levees.
• Repeated resurveys of monumented sediment ranges in the upstream Federal levee reach indicate a net loss of gravel between the levees.
• Termination of the right-bank levees theoretically provides an opportunity for transported gravels to drop out as the flow spreads out over the unrestricted floodplain.
• The evidence of progressive widening of the meander belt is consistent with the expected response of the meander belt to excessive gravel deposition in this area.

4.6.2.2. Area 4 Restoration Measures

a. Channel Alignment. The channel at this site has been extremely unstable over the last 50 years, with no identifiable, characteristic, low-flow channel pattern. The low-flow channel pattern utilizes an average meander length observed at other sites within the overall study reach, and represents a pattern that the channel may naturally assume after implementation of restoration measures. If the channel has shifted to the far right or left side of the meander belt prior to project implementation, some excavation may be required along the indicated channel alignment in order to shift the low-flow channel back to the center of the meander belt. This should be a one-time operation. The channel pattern, gravel excavation sites, and other restoration measures for Area 4 are indicated on plate 17.

b. Removal of Excess Gravel. The supply of gravel entering this site from upstream will be reduced in order to increase channel stability. Two areas were designated for gravel removal. The size of these sites has no bearing on the amount of gravel to be removed. The maximum area of disturbance during any year will be less than one-half of the delineated areas.

The Area 4 gravel removal sites were chosen for the following reasons:

• The locations provide easy access for equipment using levee access roads along both sides of the river.
• The shape and size of these sites match active gravel exchange areas at these locations, as observed in the 1996 aerial photos. The shape of the upper site was modified to allow room for partial recovery of vegetation and soil lost on a nearby wooded island since 1973.
• Location of the gravel sites along the left bank provides a high degree of assurance that gravel will be intercepted before it enters the area of greatest instability. Large cobbles will be retained during gravel removal and will be used to armor the upstream and downstream ends of the pools.

c. Pool and Channel Restoration. In addition to the gravel sites, three smaller sites were selected off of the main channel where they would be fed by spring creeks or secondary channels, and where they would be protected to some degree from direct erosive attack during flood flows. The small channels feeding and draining the two larger pools will provide opportunities for fish habitat improvement.

d. Eco-Fences. Eco-fences will be used to protect several existing islands supporting mature woody vegetation. The fences will be designed to collect debris and to slow and deflect the flow during average spring runoff periods, but they will be over-topped during extreme floods.

e. Spur Dikes. Groups of spur dikes will be located at two points along the levees. These dikes will provide velocity diversity and resting areas for fish. Properly spaced, they could provide a secondary benefit by providing increased erosion protection for a short reach of the levee.

4.6.3 Proposed Restoration Measures for Area 9

4.6.3.1 Area 9 Description

Area 9 covers a 1-mile reach of the Snake River in the vicinity of the Jackson-Wilson Bridge (see plates 4 and 18). The downstream limit is just below the Jackson-Wilson Bridge. The upstream limit is about 700 feet upstream of the Prosperity Ditch intake. The earliest available map for this area is a 1946 USGS quad sheet, which was a reprint of a 1901 map, based on 1899 topographical surveys. This map indicates that the channel was braided at that time. Within the study reach, the lower two-thirds of the channel was divided into two main channels that extended downstream through the Jackson-Wilson Bridge. Later maps and aerial photos showed a similar pattern. Rock-filled timber-cribs were used to construct bridge approach walls, four large spur dikes on the left bank, and an isolated section of levee at the Prosperity Ditch inlet. These structures were included in 1938 maps of the area. Several of the spur dikes can still be seen along the left bank upstream of the bridge.

The bridge forms a rather severe constriction in the active meander belt. During the early and middle 1950's the active channel widened considerably just upstream of the bridge. This may have been a response to unusually high flows and associated gravel deposition upstream of the bridge. Levee construction immediately upstream of Area 9 probably resulted in additional transport into this reach. The area of exposed gravel increased by 28 percent between 1944 and 1953, leaving only 15 percent of the meander belt in vegetated islands. Construction of the levees through this area in the late 1950's and early 1960's narrowed the active meander belt, funneled flows through the bridge, and probably increased the efficiency of gravel transport through this area. In 1996 there was actually more vegetative cover than in the 1950's and early 1970's. Aerial photographs indicate rather extensive gravel removal below the bridge along the left bank and at the upstream end of the study reach in the 1960's and early 1970's. Part of the removal work was for levee construction.

4.6.3.2 Area 9 Restoration Measures

a. Channel Alignment. The alignment for channels in this area follows a typical alternating pattern that has existed since about 1960. By encouraging the river to follow one or both of the selected channels some vegetation growth should be possible in areas which were frequently destroyed by the shifting channel. Some excavation will be needed, at least initially, to stabilize the channel until vegetation can become established.

b. Gravel Removal. Some gravel removal will be required to keep the selected channels open, and to provide additional flow area to offset flow resistance caused by new vegetation growth. If restoration measures are effective, only limited gravel reshaping or removal may be needed in the future. Cobble sized material will be returned to the bed and to the upstream ends of islands to retard erosion.

c. Pool and Channel Restoration. Several pool sites were selected in the protected area near the left bank levee. Sites were selected where direct exposure to the main current would be minimized. Small secondary channels connecting these pools should provide opportunities for fish habitat improvement.

d. Eco-Fences. Eco-fences are designed to reduce velocities and collect sediment, allowing the soil to rebuild and vegetation to extend out from the remnants of a wooded island. Cobble armor and anchored root wads will be used to break the force of the current and allow vegetation to become reestablished on islands between the selected channels. Abandoned bridge piers will serve as anchors for some of the fencing.

e. Spur Dikes. Groups of spur dikes will be located at three points along the levees where flow impingement or long reaches of sustained, high-velocity flow is expected. These dikes will provide velocity diversity and resting areas for fish. They will also strengthen and increase the effectiveness of the adjacent levees.

f. Bed Stabilization. A bed of rock is shown connecting the left bank levee with the debris fences. This material is designed to allow passage of flood flows while preventing the establishment of a permanent channel through the protected area along the left bank levee.

4.6.4 Proposed Restoration Measures for Area 10

4.6.4.1 Area 10 Description

Area 10 covers a 2-mile reach of the Snake River at the Gros Ventre River confluence (see plates 4 and 19). The Snake River runs south, directly into Gros Ventre Butte, then turns west in the lower half of the study reach. The earliest available map for this area is a 1946 USGS quad sheet, which was listed as a reprint of a 1901 map with some roads and other development added. The map topography was surveyed in 1899. This map depicted a braided channel pattern with up to three main branches. The Gros Ventre appeared to enter the Snake River over 1,000 feet upstream of its present confluence. A 1938 map indicated a similar degree of braiding with a somewhat different channel pattern. A 1944 aerial photograph shows the Gros Ventre channel split as it approaches the confluence with part of the flow following the old channel route and the other part entering at the present confluence location.

Aerial photos from the early 1950's indicate that the river was highly unstable with large areas of exposed gravel upstream of the Gros Ventre River and near the downstream end of the study area. However, downstream of the confluence for about one-half mile the channel was surprising stable with vegetation growing relatively close to the active channel banks. By 1960, levees had been constructed along the left side of the active meander belt. The levees followed a secondary channel, enclosing a 60 acre wooded island at the confluence. Since construction of the levees, there has been a moderate expansion of the active meander belt into the wooded riparian zone to the east. The Snake River progressively eroded the confluence island from both sides. By 1996 more than half of the island had been washed away. Additional erosion occurred in 1997. With a new channel cutting through the center of the island, the remaining trees will probably wash away within a few years.

4.6.4.2 Area 10 Restoration Measures

a. Channel Alignment. Although the channel is highly braided, the main channel has usually followed one or more of several identifiable courses through Area 10. Gravel excavation, debris fences, and a short pilot channel are designed to shift the main channel activity back into existing courses toward the center of the meander belt, taking pressure off of eroding wooded islands to the west and riparian growth along the east bank.

b. Removal of Excess Gravel. Two sites were chosen for gravel removal. The upper site captures gravel before it enters the restoration site; it directs flow down through the center of the braided area in two distinct channels. It is designed to encourage moderate channel entrenchment and increased stability of downstream channels. It should reduce pressure on eastward lands and to allow vegetation to become reestablished on interior islands. The lower site reduces gravel inflow from the Gros Ventre River and should take some pressure off of the eco-fences and remains of the wooded island to the west by drawing the main current toward the center of the excavated area.

c. Eco-Fences. Eco-fences are proposed for use to protect Bear Island and reduce flow into the eastward channel. Other fences near the center of the drawing (plate 19) will be used to restrict flow into the channel along the west levee alignment and encourage eastward accretion of the adjacent wooded islands. The pilot channel (running through Range 28) will be required to take pressure off of the downstream wooded island area and shift flow back to the center of the meander belt.

d. Pool and Channel Restoration. Restriction of flow along the west levee should encourage revegetation of this corridor and provide opportunities for aquatic habitat enhancement in the small secondary channel that remains. Two pools will be developed in this sheltered area with root wads, and other woody debris added to provide shade and shelter.

e. Spur Dikes. Groups of spur dikes will be located at three points along the levees where sustained high velocities are expected. These dikes will provide velocity diversity and resting areas for fish. They will also strengthen and increase the effectiveness of the adjacent levees.

4.6.5 Summary of Restoration Features by Project Area

The main categories of restoration measures are summarized below in table 4.6 with indication of which measures are proposed for each project area.

For each project area, four different designs of fences were evaluated. These designs included three piling eco-fences of different design specifications and one rock fence. The differences in these fence designs are described below.

a. Piling Eco-fences. Several load conditions were used in the design of the piling eco-fence. The load conditions consisted of the following:

• Impact from a floating log on a single pile.
• Impact from a floating log on a cable.
• Static hydraulic head from river flows behind the fence.

The flow velocities used to determine the force for each load condition were 5, 8, and 12 fps. These velocities are representative of the 15-, 25-, and 50-year flood flow velocities. Based on the analyses, piling type, minimum pile penetration depth, and wire rope size were determined. This information is presented in table 4.7.

Other options were considered, such as attaching a synthetic mesh or round timbers to the piling. It was determined that these options do not have the strength to withstand the river forces for the given flow conditions and were eliminated. Timber piling was also considered for piling and was found to be able to withstand the load conditions with velocities up to 5 fps. However, due to the high bedload movement in the river, timber piling was eliminated from further consideration because the timber would rapidly breakdown.

b. Rock Eco-fences. A rock eco-fence design is considered in order to investigate an alternative to a piling eco-fence that would be suitable for withstanding the high river forces. The rock eco-fences will consist of riprap with side slopes of 2 horizontal to 1 vertical and an embedment depth of at least 4 feet below the adjacent ground line. Riprap will be placed to a top elevation of 1 foot below the 100-year flood. Riprap will be sized to meet gradation 4 (table 4.6).

4.7 Array of Alternatives for the Initially Proposed NER Plan for Detailed Evaluation

The four different designs for fences, were applied with the other features, including: gravel removal; dikes; root wads; and grade control, to the initial four proposed sites. This process resulted in 16 alternatives for detailed evaluation of costs and environmental benefits in the study.

The 16 alternatives are listed in table 4.8. The column labeled "Description" indicates the design of eco-fence for each alternative.

4.8 Cost of Alternatives

This section provides cost estimates for each of the 16 alternatives and summarizes the economic analysis found in appendix E. Draft microcomputer-aided cost estimating software (MCACES) cost estimates were developed for each alternative and are summarized in section 4.8.1; broken down by: (1) construction costs; (2) real estate; (3) supervisory and administrative costs; (4) preconstruction, engineering, and design (PED) costs; and (5) O&M costs. Construction costs include components for mobilization and demobilization, materials and labor, field and home office overhead, profit, bond, and contingency. One season is assumed for construction at each site. Annual O&M costs were developed for gravel removal, site armoring, eco-fences, anchored root wads, and bank barbs. Annual O&M costs were applied for each year in the 50-year period of analysis is converted to their present value. The following tables, supported by appendix E, Economic, summarize the cost estimates for each of the 16 alternatives.

4.8.1 Study Area 1 Cost Estimates

4.9 Environmental Outputs of Alternatives

Two output measures were incorporated into the economic analyses to evaluate the efficiency and effectiveness of the 16 alternatives at achieving environmental restoration objectives: (1) aquatic habitat units ; and (2) riparian habitat units. Aquatic habitat units were measured using a model developed for the Jackson Hole study for fine-spotted cutthroat trout. Riparian habitat units were measured using the USFWS’s Habitat Evaluation Procedures palustrine/forest model for the song sparrow. The habitat evaluations indicated significant historic declines in both aquatic and riparian habitat quantity and quality since the 1950s. The habitat evaluations also predicted continued sustained declines in habitat over the 50-year period evaluated.

For each environmental variable, habitat units were estimated for each year in the 50-year period of analysis. The resulting stream of environmental outputs were summed to provide the total output stream with the project, and then divided by the number of years in the period of analysis (50) to arrive at average annual habitat units for each alternative. The change in habitat units between the without- and with-project conditions was computed for each alternative to be used as the environmental input for the cost effectiveness and incremental cost analyses. The results of these calculations are summarized in the following tables. For each project area (Project Area 1 = Alternative A; Project Area 4 = Alternative B; Project Area 9 = Alternative C; Project Area 10 = Alternative D) data is provided for alternatives 1 through 4, as wall as for the No-Action Alternative (A0, B0, C0, and D0).

Calculations were also conducted to identify the percentage change in habitat units for all alternatives. While the absolute change in habitat figures (column marked "Change") gives the appearance that aquatic benefits are much greater than riparian, the "% Change" figures indicate that in many cases, relative riparian change from the without-project condition is actually greater. The reader is reminded that the two output habitat unit categories were evaluated using different models and, therefore, the habitat units are not directly comparable with one another.

4.10 Incidental Benefits

Incidental benefits are anticipated to result from the implementation of restoration measures at the sites. These benefits have not been quantified as part of the study, but are identified here to support informed decision making. Anticipated incidental benefits include recreation benefits, flood control benefits, and reductions in existing operation and maintenance requirements for the existing flood control levee system in the proposed project area. Without further analysis and quantification of these incidental benefits, it is assumed that the benefits consistently result from each of the 16 alternatives.

a. Recreation. Potential incidental recreation benefits include higher-valued recreation experiences and opportunities in the proposed project area, including rafting and boating as well as recreational fishing. Increased fishing opportunities in the area are not expected to be in conflict with the project purpose of environmental restoration. Prevailing fishery management practices include slot limits to allow takings from only portions of the stocks which are in abundance, and the prevailing culture of recreational fisherman supports catch-and-release practices to support minimization of human impacts. Quantification of incidental recreation benefits for each alternative would require further study.

b. Flood Control. It is expected that the restoration measures under consideration have no significant impacts on flood control benefits provided by the existing Federal flood control project. It is anticipated that there may be small localized flood control benefits in the immediate vicinity of project sites resulting from increased channel capacity from gravel removal. Quantification of incidental localized flood control benefits for each alternative would require further study.

c. Operation and Maintenance. It is anticipated that implementation of restoration features will have the incidental effect of reducing existing O&M expenditures for the existing Federal levee system. Currently, low-flow channels can impinge on the inside of the levees, requiring the placement of armoring to protect the levees form erosion. Because the restoration features propose to train the river away from the levees, it is expected that reductions in O&M requirements will result. Quantification of incidental reductions in O&M costs for the existing Federal flood control project for each alternative would require further study.

4.11 Cost Effectiveness and Incremental Cost Analyses

The cost and output information presented in the previous two sections is the input for cost effectiveness and incremental cost analyses to evaluate the relative effectiveness and efficiency of the different alternatives at producing environmental outputs. Because two different and incommensurate output measures (aquatic and riparian habitat units) were required to assess the holistic effect of alternatives at restoring diverse ecosystem values, two separate analyses were conducted. Each analysis examines the production efficiency of the alternatives for each environmental output category. Following the presentation of results for each environmental category, a comparison is made to identify alternatives that exhibit exceptional performance for both output categories.

To conduct the analyses, the procedures identified in the Corps procedures manual for conducting cost effectiveness and incremental cost analyses (IWR Report #95-R-1, Corps, May 1995) were followed. These steps include: (1) display costs and outputs of alternatives; (2) identify combinable alternatives; (3) derive combinations and calculate costs and outputs; (4) identify cost-effective plans; (5) calculate and display most efficient alternatives through incremental cost analysis. To facilitate the analysis, the Corps software program, IWR-PLAN was used to perform the above steps. The results of the steps are summarized below. First, the analysis for aquatic habitat is presented, followed by the analysis for riparian habitat.

4.11.1 Aquatic Habitat Cost Effectiveness and Incremental Cost Analyses

Table 4.17 provides a display of the costs and outputs associated with each alternative. Both cost and output data are presented as "Average Annual."

The IWR-PLAN software was used to formulate all possible combinations of alternatives for restoring aquatic habitat, resulting in 625 possible combinations of alternatives called plans (including the no-action plan). Cost effectiveness analysis was next performed to identify those combinations of alternatives that (1) produce the same output as other combinations for less cost, or (2) produce more output than others at the same or less cost. The result was the reduction of the 625 possible combinations to 10 cost-effective combinations (including the no-action plan). Table 4.18 displays the cost-effective plans with their costs and outputs.

An incremental cost analysis was then conducted to evaluate the changes in cost and output from the no-action plan to all other cost-effective plans. The change in cost associated with each plan was divided by the change in output to determine the incremental cost per unit. The incremental cost per unit reflects the unit cost of providing additional output over the no-action plan. The plan that is identified as having the lowest unit cost of providing additional habitat is sometimes called the best-buy. This best-buy becomes the new baseline to which all larger-output-producing plans are compared to identify the next-best-buy. This iterative process results in the identification of the most efficient set of plans for producing increasing levels of output. The incremental cost analysis identified five best-buy plans (including the no-action plan).

The data in table 4.19 can be interpreted to support the recommendation of a plan for producing aquatic habitat. If aquatic habitat units are desired, the most efficient alternative available is C3, which provides 592 average annual habitat units at a unit cost of $775 each. If more output is desired, the next most efficient alternative is to add D3, which provides 972 additional average annual habitat units at a unit cost of $1,245 each. If more output is desired, the next most efficient alternative is to add B3, which provides 475 additional average annual habitat units at a unit cost of $4,264 each. If more output is desired, the next most efficient alternative is to add A2, which provides 46 additional average annual habitat units at a unit cost of $17,258 each.

The figure provides a graphical representation of the data in table 4.19. Incremental cost per unit is plotted on the vertical axis and output along the horizontal axis. The graph shows relatively small increases in incremental cost per unit from the first alternative (C3) to the next (D3). The increase in incremental cost per unit is larger from D3 to B3, but not as large as the jump in cost to get the last 46 units of output provided by A2.

Figure 4.1 - Aquatic Incremental Cost Analysis

4.11.2 Riparian Habitat Cost Effectiveness and Incremental Cost Analyses

Table 4.20 provides a display of the costs and outputs associated with each alternative. Both cost and output data are presented as "Average Annual."

The IWR-PLAN software was used to formulate all possible combinations of alternatives for restoring riparian habitat, resulting in 625 possible combinations of alternatives called plans (including the no-action plan). Cost effectiveness analysis was next performed to identify those combinations of alternatives that (1) produce the same output as other combinations for less cost, or (2) produce more output than others at the same or less cost. The result was the reduction of the 625 possible combinations to 26 cost-effective combinations (including the no-action plan). Table 4.21 displays the cost-effective plans with their costs and outputs.

An incremental cost analysis was then conducted to evaluate the changes in cost and output from the no-action plan to all other cost-effective plans. The change in cost associated with each plan was divided by the change in output to determine the incremental cost per unit. The incremental cost per unit reflects the unit cost of providing additional output over the no-action plan. The plan that is identified as having the lowest unit cost of providing additional habitat is sometimes called the best-buy. This best-buy becomes the new baseline to which all larger-output-producing plans are compared to identify the next-best-buy. This iterative process results in the identification of the most efficient set of plans for producing increasing levels of output. The incremental cost analysis identified five best-buy plans (including the no-action plan).

The data in table 4.22 can be interpreted to support the recommendation of a plan for producing riparian habitat. If riparian habitat units are desired, the most efficient alternative available is A3, which provides 136.70 average annual habitat units at a unit cost of $5,848 each. If more output is desired, the next most efficient alternative is to add D3, which provides 35.38 additional average annual habitat units at a unit cost of $34,205 each. If more output is desired, the next most efficient alternative is to add B3, which provides 53.09 additional average annual habitat units at a unit cost of $38,159 each. If more output is desired, the next most efficient alternative is to add C3, which provides 4.12 additional average annual habitat units at a unit cost of $111,368 each.

The figure on the following page provides a graphical representation of the data in table 4.22. Incremental cost per unit is plotted on the vertical axis and output along the horizontal axis. The graph shows a large return for investment with A3 (Area 1), then a jump in incremental cost per unit to get to the next alternatives (B3 and D3), which each provide significant output for similar incremental cost per unit. A significant increase in incremental cost per unit comes as Alternative C3 is implemented. This is largely due to the relatively small change in riparian output with the alternative. While C3 ranks last in riparian habitat production efficiency, this is in large part due to the riparian habitat demonstration project that has already been completed at Area 9 and factored into the without-project analysis. Further examination should be conducted to determine if implementing the aquatic habitat restoration features at Area 9 would provide for sustainability of benefits to be provided by the Area 9 demonstration project.

Figure 4.2 Riparian Incremental Cost Analysis

4.12 Cross-Comparison of Aquatic and Riparian Costs and Benefits

Because the project required two analyses, one for aquatic restoration and one for riparian restoration, a comparison of results was conducted to identify any plans that may be particularly effective and efficient at producing both types of outputs. This comparison is summarized in table 4.23. Table 4.23 lists the alternatives that were found to be best-buys for either output type. For each alternative, cost, aquatic habitat units, riparian habitat units, and incremental cost per unit for both habitat types are presented. In addition the table indicates whether each alternative was found to be (1) cost-effective for either habitat type, and (2) a best-buy for either habitat type. In the columns that identify if alternatives were determined to be best-buys, a number in parentheses indicates the rank of the best-buy. For example, a 1 indicates that the alternative was the most efficient at producing that output type, a 2 was the next most efficient, and so on.

4.13 Uncertainty Analysis

To examine the effect of uncertainty in cost and output estimates, an analysis was conducted that evaluated the implications of 20 percent uncertainty in cost estimates and 20 percent uncertainty in output estimates. All cost and output estimates for all 625 possible combinations were adjusted to reflect plus and minus 20 percent. A best-case scenario using the minus 20 percent adjusted cost estimates and the plus 20 percent adjusted output estimates was then analyzed for both aquatic and riparian output types. Similarly, a worst-case scenario was analyzed using plus 20 percent adjusted cost estimates and minus 20 percent adjusted output estimates. The results of these sensitivity analyses provided very similar results to those presented in the previous sections. In both the best- and worst-case scenarios, the ranking of best-buys was the same as described in the previous section, indicating that data uncertainty in the plus or minus 20 percent range should not have a significant impact on the results.

4.14 Initially Proposed NER Plan Recommendation
(See also section 4.16 for a progressive approach.)

Based upon the cost effectiveness and incremental cost analyses and the comparison of aquatic and riparian costs and benefits, Alternative D3 at Area 10 stood out as the most efficient option for producing combined habitat types, ranking second in efficiency for riparian habitat and second for aquatic. Alternative B3 at Area 4 is recommended as it is the third most efficient for riparian and the third most efficient for aquatic. Alternative A3 at Area 1 is clearly the most efficient for riparian but is the least efficient for aquatic. Similarly, Alternative C3 at Area 9 is the most efficient for aquatic although it is the least efficient for riparian. Both these sites are recommended for incorporation into a holistic ecosystem restoration plan for the study area based upon the results of the cost effectiveness analysis. The economic analysis supports the recommendation of plan A3+B3+C3+D3 as the Initially Proposed NER Plan for the Jackson Hole study. This plan corresponds to Area 1, 50-year fence design (piling), Area 4, 50-year fence design (piling), Area 9, 50-year fence design (piling), and Area 10, 50-year fence design (piling). Table 4.24 summarizes the information on the Initially Proposed NER Plan.

As presented in table 4.24, the Initially Proposed NER Plan for this Feasibility Study has an estimated total cost of $63,028,566, or an average annual equivalent cost of $4,494,280. This total cost includes $34,144,921 in total O&M costs over the project life (an average annual equivalent value of $2,435,106 per year, and a total real estate cost of $286,140. The plan is estimated to provide an additional 2,086 aquatic habitat units annually (an increase of 22 percent above the without-project condition). The plan is also estimated to provide an additional 229 riparian habitat units annually (an increase of 153 percent above the without-project condition).

4.15 Value Engineering/Initially Proposed NER Plan Refinement

Following identification of the Initially Proposed NER Plan, the Walla Walla District and the sponsor agreed with the recommendation and also with the need to evaluate opportunities to refine the project and O&M procedures in areas that may lead to cost savings without reducing project performance. In response, the Walla Walla District study team conducted a value engineering exercise to refine the plan’s preliminary cost estimate and examine, identify, and incorporate cost savings into project construction, operation and maintenance. This section identifies the changes to the Initially Proposed NER Plan resulting in cost savings and evaluates the impact of such changes on plan formulation.

Savings were identified in three primary areas:

• Reductions in component quantities.
• Reductions in construction cost.
• Reductions in O&M cost.

4.15.1 Refinement of Quantities

The Initially Proposed NER Plan includes restoration alternatives for Areas 1, 4, 9, and 10 (see plates 4, and 16 through 19). Plan elements include gravel removal, site armoring, piling eco-fence, anchored root wads, and riprap structures such as kickers, bank barbs, and grade controls. Approximate quantities for the major components of the Initially Proposed NER Plan are summarized in table 4.25. Changes in quantities from those used in the preliminary estimate to those used in the refined estimate are indicated in the table.

As indicated in the table, the major reductions in quantities come in the area of gravel removal estimated to be required for excavation of sediment traps and stabilization of the channel. There is a net decrease (across all sites) in the quantities required for armoring and spur dikes. Quantities estimated for eco-fences, anchored root wads, and rock grade control are not changed in the refined estimates.

4.15.2 Refinement of Unit Costs

All reductions in unit costs in the refined cost estimates are attributable to the identification of a closer disposal site for dredged material. Initial cost estimates for disposal of dredged material were based upon use of a disposal site located approximately 12 miles from the proposed project sites. A closer disposal facility was identified approximately 5 miles from the project sites, reducing disposal costs. Other unit costs remained unchanged from the preliminary estimates.

4.15.3 Refinement of Operation and Maintenance Costs

Due to concerns about the high cost of annual maintenance following initial construction of the project, the requirements for gravel removal were revisited. The preliminary estimates reflected the maximum reasonable expected requirements based upon the available information at that time. Subsequent sediment range resurveys indicated that the actual gravel requirement is likely much less than the original estimate (reflected in the refinement of construction quantities, section 4.15.1) and may be zero after some years at one or more of the proposed restoration sites. Based upon this new information, the costs for removal of gravel for channel capacity and sediment traps was reduced to more accurately reflect actual expected values over the project life. This reduction in annual maintenance requirements resulted in significant cost reductions.

4.15.4 Summary of Initially Proposed NER Plan Refined Costs

Table 4.26 presents the effects on summary cost categories of the value engineering cost refinements in the areas of construction quantities, unit costs, and O&M quantities.

Table 4.26.A summarizes the refined cost estimates for each component of the Initially Proposed NER Plan as well as for the plan as a whole. Table 4.26.B summarizes the cost estimates described in section 4, Plan Formulation. Table 4.26.C summarizes the change in cost from the preliminary estimates to the refined estimates. Table 4.26.C shows the reductions in each cost component for the Initially Proposed NER Plan to be as follows:

• Construction, PED, and Supervisory/Administrative costs were reduced by $1,909,645.
• O&M Costs were reduced by $25,247,192.
• Total Costs were reduced by $27,156,837.
• The average annual equivalent value of total costs were reduced by $1,916,129 per year.

4.15.5 Impact of Cost Reductions on Plan Formulation

Because of the significant reductions in the Initially Proposed NER Plan’s cost (as identified in section 4.15.4) the study team assessed the impacts of the refined costs on the plan formulation process documented in earlier parts of section 4. It was determined that the cost reductions would have no impact on the selection of Design Alternative 3 (differentiated by the 50-year piling eco-fence) at each of the sites because the cost reductions would apply consistently to all alternatives at each site. Therefore, the rationale for selecting Alternative 3 at each site would hold in a new cost effectiveness and incremental cost evaluation.

However, the reductions in cost were determined to have differing impacts on the different study areas (for example, a significant change in construction costs was tied to the identification of a closer site for disposal of dredged material. As some study areas require more excavation than others, this change would affect different sites inconsistently. To assess the impact on formulation of the Initially Proposed NER Plan, an analysis was conducted to determine the relative cost effectiveness of the individual components of the plan (A3, B3, C3, and D3) with the refined costs estimates. The results of the refined incremental cost analyses for each output type (aquatic and riparian) are presented in figure 4.3 and 4.4 on the following page. A discussion of the reductions in incremental cost and the impacts on formulation of the plan follow the incremental cost graphs.

Figure 4.3 Refined Aquatic Incremental Cost Analysis

Figure 4.4 Refined Riparian Incremental Cost Analysis

4.15.5.1 Refined Aquatic Cost Analysis

The incremental cost analysis for restoration of aquatic habitat produced the same sequence of recommended components with the refined costs as with the preliminary costs. The amount of output provided remained constant while the incremental cost per unit decreased across the board. As with the earlier analysis using preliminary costs, the most efficient option was identified as C3 (Area 9). Alternative C3 provides 592 habitat units at an annual unit cost of $540 each. This unit cost is down from $775 each based on the preliminary estimate. The second most efficient alternative in both analyses (using preliminary and refined estimates) was D3 (Area 10). D3 provides 972 habitat units at an annual unit cost of $680 each (down from the unit cost of $1,245 each with the preliminary cost estimates). Next in the efficiency rankings in both analyses was B3 (Area 4). B3 provides 475 habitat units at an annual unit cost of $1,740 each (down from a unit cost of $4,264 each with the preliminary cost estimates). Ranking last in efficiency for restoring aquatic habitat was Alternative A3 (Area 1), which provides 46 additional habitat units at an annual unit cost of $16,420 each (down from $17,258 with the preliminary cost estimates). The percentage reduction in incremental unit costs are summarized below:

• Area 9 (Alternative C3) - Incremental unit cost reduced by 30 percent.
• Area 10 (Alternative D3) - Incremental unit cost reduced by 45 percent.
• Area 4 (Alternative B3) - Incremental unit cost reduced by 60 percent.
• Area 1 (Alternative A3) - Incremental unit cost reduced by 5 percent.

Based upon these results there is no impact of using the refined costs that changes the results of the formulation of the Initially Proposed NER Plan based upon aquatic incremental cost evaluations.

4.15.5.2 Refined Riparian Cost Analysis

The incremental cost analysis for restoration of riparian habitat produced a similar sequence of recommended components with the refined costs as with the preliminary costs. The amount of output provided remained constant while the incremental cost per unit decreased across the board. As with the earlier analysis using preliminary costs, the most efficient option was identified as A3 (Area 1). Alternative A3 provides 136.70 habitat units at an annual unit cost of $5,530 each. This unit cost is down from $5,848 each with the preliminary estimate. The second most efficient alternative in both analyses (using preliminary and refined estimates) was B3 (Area 4). B3 provides 53.09 habitat units at an annual unit cost of $15,560 each (down from the unit cost of $38,159 each with the preliminary cost estimates). Next in the efficiency rankings in both analyses was D3 (Area 10). D3 provides 35.38 habitat units at an annual unit cost of $18,570 each (down from a unit cost of $34,205 each with the preliminary cost estimates). Ranking last in efficiency for restoring aquatic habitat was Alternative C3 (Area 9), which provides 4.12 additional habitat units at an annual unit cost of $77,520 each (down from $111,368 with the preliminary cost estimates). The percentage reduction in incremental unit costs are summarized below:

• Area 1 (Alternative A3) - Incremental unit cost reduced by 6 percent.
• Area 4 (Alternative B3) - Incremental unit cost reduced by 60 percent.
• Area 9 (Alternative D3) - Incremental unit cost reduced by 45 percent.
• Area 10 (Alternative C3) - Incremental unit cost reduced by 30 percent.

The cost effectiveness rankings of B3 and D3 were reversed, but the relative increase in incremental cost between the two is reasonable and both are recommended. Based upon these results there is no impact of using the refined costs that changes the results of the formulation of the Initially Proposed NER Plan based upon riparian incremental cost evaluations.

4.16 The Progressive Plan

4.16.1 Plan Recommendation

The Corps conducted this Feasibility Study of the Snake River near Jackson Hole, Wyoming, from August 1996 to January 2000. An alternative formulation briefing was held in July 1999, and the study results (pending resolution of several issues) were approved for public release with concurrent HQUSACE review. At that time, the proposed project covered approximately 5 miles of the 22-mile stretch of the Snake River that had been authorized for study.

During a site visit in October 1999, Headquarters staff recommended that the District Project Manager consider using the cost and benefit information gathered for the 5-mile study area (presented in this report as the Initially Proposed NER Plan) as a proxy for the entire 22-mile reach. The rationale is that the applicable engineering measures had already been identified, the benefits of the management measures had been evaluated, and the construction costs had been developed. Therefore, the District could use the site-specific information to formulate a complete plan to restore the entire degraded area. The complete plan developed by the district is presented as the Progressive Plan in this report.

4.16.2 Plan Formulation of the Progressive Plan

At the point that the Initially Proposed NER Plan was formulated, the Feasibility Study had conducted five levels of plan refinement: (1) significance based preliminary screening; (2) formulation of initial alternatives; (3) cost effectiveness and incremental cost analyses; (4) uncertainty analysis and value engineering; and (5) NER plan refinement. The sixth level of analysis used to address the entire 22-mile reach of the Snake River is based on the refined cost and benefits of Areas 1, 4, 9, and 10. In order to select restoration tools and features for the Progressive Plan, the study team analyzed recent aerial photographs, floodplain cross-sectional data, and results of the sponsor-constructed demonstration project as represented in the Final Report: Snake River Restoration Demonstration Project, prepared by Teton Conservation District (included in the supplementary section of this study).

Although the study team identified eight additional sites for restoration, these locations are based on current information and may change due to the unpredictable and dynamic nature of the Snake River in this 22-mile reach. The sites that have been identified and proposed for restoration measures have been analyzed in this planning process as our best estimate during the 12-year monitoring and construction schedule. The measures used at selected sites will be adapted and applied at different sites, if necessary and applicable, as the Snake River changes over the following years. Table 4.27 presents the configuration of restoration measures for the Progressive Plan.

In addition, a new project cost estimate was developed based on a progressive project construction and monitoring plan. This approach takes into consideration the complexity of the restoration effort and applies an efficiency curve that represents the anticipated benefits of phased construction, monitoring and adaptive management. The progressive estimate assumes that the cumulative knowledge of phased construction, monitoring, and adaptive management will result in cost reductions. The approach resulted in a significant reduction in total project cost and reduces monitoring costs to 4 percent of the total project cost. The first site constructed would be phased over a 6-year period to allow refinement and fine tuning of restoration features. The construction period would then be reduced for each consecutive area until a three-year construction phase is reached. Table 4.28 illustrates the initial construction, continuing construction, and monitoring phasing and provides project cost by area, and details Federal and Sponsor fully funded costs.

Table 4.28 - Construction & Monitoring and Cost Timeline

4.16.3 Cost Effectiveness and Incremental Analysis

The IWR-PLAN software was used to formulate all possible combinations of alternatives for restoring aquatic and riparian habitat for the Progressive Plan. Areas A through H were compared with the areas studied in formulation of the Initially Proposed NER Plan. Cost effective analysis was next performed to identify those combinations of alternatives that produce the same output as other combinations for less cost, or produce more output than others at the same or less cost. Table 4.29 displays the cost-effective alternatives with their costs and outputs.

As presented in table 4.29, the Progressive Plan reduces the average cost per benefit unit starting with Area E at $1,600 each to Area G at $1,270, to Area H at $1,143, to Area F at $ 1,006 to Area C at $980 before increasing slightly in Area A to $997, Area D at $1,015 to Area B at $1,063.

Figure 4.5 provides a graphical representation of the data in table 4.29.

Figure 4-5 Cost Effectiveness of Progressive Plan

The eight additional Progressive Plan sites’ average cost per benefit unit are all less than the composite average cost for the Initially Proposed NER Plan sites.

4.16.4 Plan Summary

Based on the cost effectiveness and incremental cost analysis, the Progressive Plan is recommended as the preferred alternative for construction. This plan builds upon the efficiencies gained in the Initially Proposed NER plan (Areas 1,4, 9 and 10) and leads to greater efficiencies for the remainder of the impacted 22-mile reach of the Snake River. Table 4.30 summarizes the information on the proposed Progressive Plan. In order to estimate projected performance under the Progressive Plan, the progressive sites were assigned a commonality factor as compared Areas 1, 4, 9 or 10. For Areas A & B, the factor is 1.2 times Area 4; for area C, 0.8 times Area 9, for Areas D and E, the same as for Area 9; for Area G, 1.2 times Area 10; for Area H, 0.8 times Area 10. The same assumptions used to generate tables 4.13. and 4.14 for the Initially Proposed NER Plan, where habitat is lost at a progressively increasing rate, were used to develop table 4.30.

MCACES estimates reflecting the Total Construction costs in table 4.30 are provided in appendix G, Cost Estimates. The Progressive Plan is estimated to provide an additional 8,189 aquatic and 489 riparian average annual habitat units. Respectively, 409,450 and 24,450 habitat units will be created during the 50-year period.

In table 4.31, the Progressive Plan is compared to the without project predicted habitat evaluation for the entire 22-mile stretch of the Snake River under consideration. Initial habitat units for the 22-mile stretch is extrapolated from the Initially Proposed NER Plan data. It is estimated that the combined habitat output for the eight progressive sites would be two times the initial four sites combined habitat output (hence a multiplier of three times the Initially Proposed NER Plan). This is a conservative estimate since the habitat at the eight progressive sites is poorer than at the four initial sites, which can be inferred from high (poor) scores assigned to the majority of the progressive sites (see table 4.4). Table 4.31 also indicates that, when compared to the Without Project Alternative, the Progressive Plan will result in a 50-year cumulative habitat impact difference (465,000 aquatic and 39,325 riparian habitat units, or 28% and 137% increase respectively).

Table 4.32 compares the Progressive Plan against the Initially NER Proposed Plan. In terms of average annual habitat units, the Progressive Plan would generate a 293% aquatic and a 100% riparian habitat unit benefit, with a cost increase of 83%.

In conclusion, the Initially NER Proposed Plan sites were selected based on the multiobjective analysis presented in table 4.5 (and appendix A). Using the selected criteria and specific weighting factors, six sites were identified as providing the greatest overall opportunity for environmental restoration. Using sponsor input to factor in property ownership and cultural concerns, the list was reduced to the four sites recommended in the Initially Proposed NER Plan as those sites with the best opportunity for both environmental restoration and project implementation. While the Progressive Plan includes the eight sites that were not selected by the multiobjective analysis, the cost effectiveness and incremental analysis identified that the added sites produce less cost per habitat unit generated as illustrated in tables 4.29 and 4.32. The economic analysis supports the recommendation of the Progressive Plan as the proposed NER Plan for the Jackson Hole Feasibility Study.

5. DESCRIPTION OF INITIALLY PROPOSED NER PLAN AND THE PROGRESSIVE NER PLAN

5.1 NER Plan Benefits Simulation

The overall effect of the proposed NER Plan is best shown in the computer-generated oblique aerial views of the without- and with-project conditions at Area 9. Plate 20 shows the existing condition (looking downstream) of the Snake River between the levees. The channel is largely devoid of vegetation, which is confined to islands located near the left bank levee. In the future, without-project condition (plate 21) the flows between the levees will continue to rework the gravels in the channel and will remove all but a few very small remnants of the currently existing islands.

Plate 22 shows the with-project condition immediately after construction. Here eco-fences are placed on the right side of the vegetated island to the left-center of the view and anchored root wads are placed on the upstream edges of the unvegetated island in the center of the view. Channel capacity excavations are visible in the main channel and secondary channels are excavated between islands on the left. Spur dikes are added to protect the right-bank levee from impinging flows and to train the current more toward the center of the channel.

In the near future, 5 to 15 years hence, sediment is trapped and vegetation has begun to establish along the fences and root wads (plate 23). Twenty years hence, vegetation has increased and is reinforcing the islands (plate 24). Fifty years hence, the vegetation is fully matured and well established (plate 25). Throughout the project life, flow capacity in the main channel as well as the secondary channels will be maintained by periodic gravel removal. Elements of the overall restoration plan are described in section 5.2 below.

5.2 NER Plan Features

5.2.1 Piling Brush Eco-Fences

Eco-fences block, slow down, or deflect the force of the river current during high-flow periods in order to protect existing islands and vegetation and cause deposition of sediment where new vegetation may become established. Eco-fences allow the river to heal itself. Rather than the costly and disruptive process of placing fine sediments with heavy equipment, the river will be allowed to do the work through a natural process. See plates 16 through 19 for general eco fence locations.

Eco-fences will be placed at the upstream end and along the sides of existing wooded islands to prevent or inhibit further soil and vegetation loss. These fences will also be placed in areas where soil and vegetation have already been lost to facilitate deposition and vegetation regrowth (plate 30). As vegetation becomes established, it will further slow flow velocities and encourage accelerated sedimentation. Indirect aquatic habitat benefits will be gained as vegetation is reestablished (plate 31). As the amount of vegetation increases (plate 32), shade and material (such as leaves and insects that fall into the river, providing nutrients to river organisms) will also increase while ensuring future availability of large woody debris in to the river.

Two different types of fences: piling eco-fences and rock eco-fences, may be used. Piles will be driven and have interconnecting cables attached. Rock eco-fences, constructed of riprap, will require excavation to key the structure into the cobble, gravel, and sand substrate. Excavated material will be scooped and transported off site for upland disposal. Riprap will be trucked to the site and dumped directly into the excavations. Riprap used to construct the rock eco-fences will be large, angular rock, free of fine sediment.

5.2.2 Secondary Channels

Secondary channels, also referred to as side channels, are typically smaller channels, which parallel the main river channel (see plate 27). Secondary channels vary in size and depth and may carry flows year-round or only during periods of high water. These channels help disperse flows and suspended sediments throughout the floodplain; they provide valuable aquatic habitat.

Secondary channels will be constructed in selected locations to improve flows to existing off-channel pools or provide flows to newly constructed pools. See section 5.2.5 for discussion of off-channel pools. Some secondary channels exist within the leveed sections of the river. However, because of accelerated flows, these existing channels are degraded or plugged. Gravel and cobble will be excavated to either enhance existing secondary channels or to construct new channels.

Because of the remote locations and potential disturbances to wetland and riparian vegetation by trucks accessing the excavation sites, dredged cobble, gravel, and sand will either be scooped and side-cast on the adjacent gravel deposits or transported from the site for upland disposal. The determination of whether to side-cast material or transport it from the site will be based upon the potential impacts of ingress and egress of trucks to the site. If dump truck access routes having minimal disturbance upon vegetation are available, the material will be scooped and transported to a permitted gravel processing facility for disposal. Excavated gravel and cobble may be screened, depending upon the proximity of the site to the gravel screening area and anticipated need for +4 inch cobbles to rearmor excavation sites. Side-cast material will be uniformly spread on adjacent unvegetated gravel deposits below the ordinary high-water mark in the dry and above the low flow of the river. Fine sediments such as silts and sands will be placed in locations to promote riparian habitat restoration.

5.2.3 Gravel Removal

Gravel removal will be used to varying degrees in the implementation of the various environmental restoration tools to provide more channel stability and provide sediment deposition in controlled areas. Principally gravel removal will be used to improve fish habitat, compensate for reductions in channel capacity, increase channel stability, and improve sediment transport. Gravel removal will be used to construct channel stabilization pools, secondary channels, and off-channel pools. It will also be removed from specific areas of the channel to compensate for the decreases in channel capacity. All gravel removal will be accomplished using a track-mounted excavator, rubber-tired backhoe, or other similar equipment along with trucks to transport the material to disposal and stockpile sites.

Areas (from which gravel is removed to maintain channel capacity and to construct channel stabilization pools and off-channel pools) will be rearmored on the bottom surface using cobbles screened from the excavated material. Gravels, which are removed, will be either transported to a site located between the levees for screening or will be transported as unscreened material to an existing gravel processing facility off site. Screening will separate out cobbles +4 inch in diameter or larger for use as armoring material. It may be necessary to temporarily stockpile the screened material.

If a site between the levee is used, the -4 inch waste material will be transported from the screening location by truck to a temporary sponsor-provided off-site upland disposal site prior to anticipated high flows. The +4 inch cobble will be transported by dump truck from the screening site to the channel capacity, side pool, and channel stabilization pool excavation sites and placed to rearmor the disturbed bed. The material will be dumped in wind-row fashion, perpendicular to the normal stream flow to allow subsequent high flows to naturally disperse the material. The +4 inch cobble will be placed prior to anticipated high flows.

5.2.4 Channel Capacity Excavations

Channel capacity excavation will be used to offset reductions resulting from construction of the environmental restoration tools and effects of the tools upon channel structure and function. Additionally, channel capacity excavation will compensate for ongoing channel aggradation and loss of channel capacity. Channel capacity will be reduced by the installation of anchored root wad logs; discharge of riprap to construct rock eco-fences, spur dikes, and rock grade control; and from the deposition of bedload material and resultant regeneration of vegetation. Bedload deposition will be intentionally triggered by structures such as the eco-fences and anchored root wad logs. Channel capacity excavations will be necessary to compensate for the effects of the environmental restoration project and maintain the 100-year base flow for flood protection (see plate 26).

5.2.5 Channel Stabilization Pools

Channel stabilization pools reduce flow velocity, catch bedload material, and reduce the transport of bedload material to downstream areas, which may already have an over abundance of material. These functions improve channel stability and may improve fish habitat through the creation of a large pool. Channel stabilization pools will be excavated in strategically selected locations to trigger the deposition of bedload material and sediments.

5.2.6 Off-Channel Pools

Off-channel pools provide important rearing habitat for fine-spotted cutthroat trout. Access to potential spawning areas in spring creeks and secondary channels and pools has been severely reduced by construction of the levees. This lack of adequate spawning habitat is considered a major limiting factor for fine-spotted cutthroat trout in the Snake River.

Off-channel pools will be constructed within the alignment of the secondary channels to provide rearing habitat for fine-spotted cutthroat trout (plate 28). Some existing pools will be used and may only require limited excavation to enhance their function. Other pools will require complete excavation. Excavated cobble, gravel, and sand will be either scooped and side-cast on the adjacent gravel deposits or transported from the site for upland disposal. Depending upon the proximity of the site to the gravel screening area and anticipated need for +4 inch cobbles, the excavated gravel may be screened. Side-cast material will be uniformly spread. Side-casting will occur below the ordinary high-water mark in the dry, and above the low flow of the river.

The determination of whether to side-cast material or transport it from the site will be based upon the potential impacts of ingress and egress of trucks to the site and the opportunity to enhance riparian habitat as described above. If dump truck access routes that have a minimal disturbance on vegetation are available, the material will be scooped and transported to a permitted gravel processing facility for disposal.

5.2.7 Spur Dikes

Spur dikes will provide areas of resting habitat close to areas of high velocity, which may transport high quantities of aquatic insects used as food by fine-spotted cutthroat trout and other species and provide protection against bank erosion. Spur dikes will be installed in areas where stream velocity is normally too high for fish to spend much time. These resting areas may be further enhanced with the incorporation of large woody debris on the downstream side. The large woody debris will be placed in areas of ineffective flow.

Spur dikes consist of a series of either kickers or bank barbs extending into the channel from the adjoining levee (plate 29). Riprap used to construct the spur dikes will consist of large angular rock, free of fines. It is likely that spur dike construction will require in-water work. Both kickers and bank barbs will be composed of riprap armor. Kickers may extend as much as 60 feet from the levee. Random fill excavated to embed the kickers will be used as the core material. Equipment used to excavate for the kickers and to place riprap will sit atop the levee and will maneuver onto the top of kickers, when necessary. Bank barbs, which are smaller than kickers, will extend up to 30 feet into the channel from the levee. Both types of structures will be embedded into the levee.

5.2.8 Anchored Root Wad Logs

Anchored root wad logs consist of tree trunks with the root attached. Depending on placement, anchored root wad logs may provide additional resting habitat for fine-spotted cutthroat trout and other fish species. The 1989 Jackson Hole Debris Clearance Environmental Assessment found that "local scour and fill is also evident adjacent to woody debris left in the channel following the 1986 flood." Anchored woody debris may also encourage sediment deposition and help establish new vegetation (plate 33).

Anchored root wad logs will be obtained from along the river channel within the four project areas or from commercial sources. Logs will be transported to the installation site by truck, rubber-tired skidder, or helicopter. A backhoe may be used to level an area to place the logs so that the logs would have uniform bearing along the trunk and its root would be partially embedded. The logs will be fastened down with toggle bolt anchors. The anchors will be driven into the ground with a jackhammer and a jack will be used to pull up on the anchors locking them into place. The cable will be tied around the logs and cinched down to tighten the logs to the ground.

5.2.9 Rock Grade Control

Rock grade control structures keep the river from eroding and destroying existing riparian areas. Riprap will be placed at specific areas where down-cutting of the channel threatens channel stability. Existing cobble, gravel, and sand will be removed to a standard uniform depth of 3 feet below the ground surface. The material will be scooped and transported off site for upland disposal. This area will then be graded and refilled with riprap to match existing topography. Riprap will be transported to the site by truck, dumped, and spread using the anchor track-mounted excavator. Riprap used to construct the rock grade control will be large angular rock, free of fine sediments.

5.3 Monitoring

Two types of monitoring will take place. Compliance monitoring will take place during construction and during any maintenance activities. This monitoring will ensure that environmental laws and regulations are followed. Compliance monitoring will ensure compliance with various requirements identified in appendix H, Environmental Assessment, which contains its own appendix A, Biological Assessment, and appendix B, Fish and Wildlife Coordination Act Report. Elements in the Project Performance Monitoring Plan will be conducted following completion of construction to assess project environmental performance. Changes to aquatic and terrestrial habitat to identify effects of river flows on the structures, as well as effects of the structures on the river will be documented.

The Project Performance Monitoring Plan will remain in effect throughout the construction process. The cost of compliance monitoring is included in construction costs. Project Performance monitoring is estimated at one percent of the total construction cost ($364,000). Adaptive management costs are estimated at three percent of the total construction costs ($1,093,000).

5.3.1 Project Performance Monitoring Plan

The purpose of the Monitoring Plan is to assess the effectiveness of the restoration features in improving aquatic and terrestrial habitat. The plan will assess the functional performance of the restoration tools, and document the environmental benefits achieved by the project. The plan is provided in full as appendix F to the Environmental Assessment (appendix H to this study). Results obtained through monitoring will enable the Corps and the local sponsor, through coordination with local agencies, regulatory authorities, landowners, and other interests, to make informed decisions concerning management of the project to obtain the planned performance. The Monitoring Plan will also build an information base to support future restoration decisions regarding the design and performance of the restoration measures.

Project performance monitoring is an evaluation of how well the project is meeting the environmental goals. Project performance reports will be prepared about every fourth year, documenting changes in the habitat conditions.

Adaptive management will be preformed on specific restoration tools to fine-tune their function using survey information from the continuing construction phase and Performance Monitoring Plan. Adaptive management could include the implementation of project modifications, repairs, or added features that may be necessary for any unforeseen circumstances that may impair project performance.

5.3.2 Project Maintenance

At the end of the monitoring period, and upon receipt of the O&M manual, the local sponsor will assume normal operating, maintaining, replacing, repairing, and rehabilitating (OMRR&R) responsibility for the project, which may include longer-term monitoring to be conducted as part of the local sponsor’s O&M responsibilities. Such future requirements will be funded entirely by the local sponsor.

During the first few years of use, an elevated level of maintenance is expected until the system stabilizes and information is gathered that may identify more efficient uses of structures. Certain structures are likely to require maintenance to ensure they continue to function as designed. The shifting nature of the braided river is expected to have some effect upon the structures; however, the extent of effects will vary between structures and from site to site depending upon river conditions. Some structures may require only minor maintenance while others might require more substantial reconstruction. The frequency with which maintenance may be necessary and the extent of necessary repairs will be dictated by the frequency and extent of river effects upon the structures. Maintenance will likely be necessary to maintain and ensure the proper function of eco-fences, secondary channels, channel stabilization pools, and off-channel pools. Maintenance is not expected to be necessary on the remaining environmental restoration tools; however, monitoring will be necessary to assess the need for maintenance.

It is unlikely that vegetative growth from the environmental restoration project will adversely impact flood control. The channel typically has adequate room to adjust its location and conveyance. This is particularly true if the channel alignment is stabilized and excessive erosion is reduced. The designated mid-channel pool areas will provide a means of maintaining adequate conveyance by removing excessive gravel before it has an opportunity to build up in the channel. However, it will be important to assure that "maintenance" does not involve activities that progressively increase the cross-sectional area of protected vegetation at any point along the channel beyond that indicated in the original design drawings.

Maintenance of environmental restoration tools will be conducted in accordance with the limitations and restrictions of the EA (appendix H) and its appendixes. The local sponsor may be responsible for acquiring some state or local permits necessary to implement maintenance.

5.3.2.1 Eco-Fences

Maintenance measures for the eco-fences should provide for minimal adjustment of fence lengths or alignment, repair of damaged cables or piling, and reestablishment of the fence tie-off to the bankline if erosion damage threatens to destroy the function of the fence, increase bank erosion, or threaten adjacent flood control structures. This could involve removal of some portions of fence if it proved to be poorly aligned or improperly located.

Maintenance will most likely be necessitated by failed posts and fencing or by erosion around the landward end of the fence. Repairs will involve reestablishment of the fence tie-off by extending the fence back to the undisturbed bankline, repositioning existing piles and cable, installing longer posts, reattaching the cables, or adding other material to trap debris. In some cases, it might be sufficient to drive and attach additional supporting posts in locations where the fence is beginning to sag or fail. Work will be done during low flows.

Depending upon how the river affects the fence site, maintenance work may or may not occur in the water. If a fence is failing to catch debris, trapping efficiency might be increased by adding a finer mesh screen that will capture smaller debris, or exposed areas may be cov-ered by dragging some of the debris over to places where it is deficient. If debris is failing to be trapped or is being de-flected around the fence, it may be necessary to add one or more fence panels oriented upstream near the end of each fence. In some areas, adjustments in the location or angle of eco-fences may be needed if the river abandons the channel.

5.3.2.2 Secondary Channels

The deposit of gravel and subsequent blockage of the upper end of the channel would necessitate maintenance. If groundwater is inadequate, the secondary channels will need to be reopened to provide an adequate inflow of water for the downstream pools. Gravel blockages will be excavated sufficiently to provide 2 to 3 (cfs) flow. Excavated gravel will be side-cast due to the anticipated small quantity.

5.3.2.3 Channel Stabilization Pools

The quantity of sediment being transported downstream cannot be precisely calculated and is expected to vary from year to year. Because of this, the optimum size of channel stabilization pools, and their anticipated effectiveness, is not known. Removal of gravel from channel stabilization pools (i.e., sediment traps) as part of O&M will generally occur when one-half or more of the original gravel volume of the pool is refilled. Only about 50 percent of the original pool area will need to be disturbed to remove the quantity necessary to maintain the trap. Excavation will not vary from or exceed the original design. The pools will have to be closely monitored to ensure excessive excavation does not occur. Under average conditions, several years may be necessary to fill a channel stabilization pool; however, it is possible that a single flood event could fill one completely. Experience over time will determine the appropriate level of maintenance.

5.3.2.4 Off-Channel Pools

Off-channel pools will be subject to refilling during high-flow seasons. Pools that are close to the main channel could be refilled with gravel and cobbles in a single high-flow season. Those farther away will likely last a number of years, refilling with silt and sand brought in by the interconnecting channels and by general overbank flow during high-flow periods. Due to the braided nature of the river, it is nearly impossible to select locations where pools would always be protected from potential destruction by major flood flows or channel changes. Based on this, various approaches to maintaining off-channel pools will be used.

Pools near the margins of the active meander belt will be allowed to fill completely. A new pool will then be constructed nearby, without disturbing the old pool or its water supply. Where possible, the new pools will be built either upstream or downstream of the existing pools in order to use the same supply channels. Pools constructed near the main channel in the vegetation-free areas of the channel will be reexcavated only when completely filled with gravel. These channels could be filled in completely during a major event, which could also involve major changes in the main channel. The main channel may even cut a course through the center of a pool. In the latter case, the pool will be reexcavated at another location (probably along the previously abandoned channel). The objective will be to approximately maintain the same area of pools throughout the life of the environmental restoration project either by re-excavation at the same location or relocation of a pool to a more advantageous site. Maintenance will be performed during the low-flow period.

5.3.2.5 Spur Dikes

Spur dikes will occasionally be damaged by high flows. Measurements, taken at various locations on the existing channel, indicate that erosion can extend down to at least 15 feet below the high-water level. The mode of damage most likely to occur will be undercutting of the toe of the dike and collapse of material into the void with material being transported downstream. Maintenance of bank barbs or kickers will generally involve reestablishment of the toe and restoration to the original geometric outline. Maintenance could include placement of additional bank or toe protection, strategic placement of boulders or intermediate barbs to break up the undesirable flow pattern if undesirable flow patterns are created. In a worst-case scenario, the spur dike group can be removed. As a result, spur dikes are not anticipated to need maintenance in order to achieve the desired aquatic habitat benefit and performance measurement goals. It is anticipated that a staged construction sequence will allow design adjustments to be made as experience is gained from the performance of these structures.

5.4 Real Estate

The real estate needs described below are for the Initially Proposed NER Plan and thus reference Areas 1, 4, 9, and 10. Real estate requirements for the Progressive Plan will occur during the PED phase for each specific additional site. Real estate requirements, such as coordination, easements, and assignments will be conducted with property owners and the BLM. No new requirements are anticipated beyond those addressed in appendix F, Real Estate or in this section of the Study (section 5.4). Unforeseen requirements will be carried out by the non-Federal sponsor in coordination with the Corps. This proposed environmental restoration project will occur upon privately owned lands and lands administered by the BLM. Lands will be altered through the removal of gravel and placement of materials to construct the environmental restoration tools. These alterations, however, would not eliminate any current land uses identified above or introduce any new land uses. The local sponsor will obtain real estate instruments, which the Government identifies as necessary for implementation of environmental restoration work on Federal and private lands.

5.4.1 Ownership Data

Property ownership and estimated individual tract requirements within each of the project areas are shown in appendix F, Real Estate, and summarized below. In some instances there are multiple parcels located within the proposed sites that are under single ownership. In those cases, each parcel will be treated individually with site-specific easement language.

Area 1	Encompasses an area of approximately 360 acres. Given the current location of the thread of the active river along the west edge of the floodplain, four ownerships are recognized as being affected by the proposed project. Two private ownerships and one public ownership (BLM) are located within the site, and one private ownership will be affected by access to the site.
Area 4	Includes approximately 157 acres within 9 riparian ownership’s ranging from 4 to 32 acres. Six of the parcels are from 13 to 32 acres, the other four are smaller.
Area 9	Includes approximately 89 acres within 11 riparian ownership's ranging from 0.5 to 70 acres. Seven of the parcels are from 0.5 to 1.5 acres. One BLM tract is 70 acres.
Area 10	Includes about 335 acres within 13 ownership's ranging from 10 to 65 acres per tract with 8 parcels 10 to 65 acres and 7 ranging from 1 to 9 acres each.
Areas A-H	Real Estate requirement to be conducted during the PED phase prior to construction.

5.4.2 Real Estate Requirements

Real estate requirements are based upon site maps with restoration features located given the existing geomorphology as of the year the aerial photos were taken and do not necessarily represent the actual projects.

a. Existing Easements. To the maximum extent possible, the Federal Government and the non-Federal sponsor will use existing easements to implement the restoration project. However, in most cases the physical boundary limitations of the existing flood control easements do not completely encompass the areas required for the proposed project, therefore additional easements will be required.

b. Additional Easement. Where restoration features are proposed for a parcel where an easement does not exist or is insufficient, an appropriate easement for ecosystem restoration will be procured by the sponsor on a willing-seller basis. The easement will be for the purpose of restoring the Snake River’s natural environment, and will be crafted to acquire only the rights needed for the particular restoration features to be located on that particular parcel. For parcels on which access rights do not exist or are insufficient, the non-Federal sponsor will acquire a road easement estate if required for permanent access. For temporary access, rights will be acquired under a temporary work area easement or temporary road easement.

c. Special Requirements. The BLM is the land manager on three parcels within the Initially Proposed NER Plan restoration areas. The BLM does not currently have a land management plan in place for the land along the Snake River. As required by BLM, any sand or gravel removed from the BLM parcels under the free use permits will be used for the project or other public purposes only. The sponsor will not claim a credit for the value of these materials. Any temporary stockpile sites required during the restoration project will be provided on sponsor-owned lands or rights-of way. If any new temporary stockpile sites are required, the sponsor will acquire temporary work area easements for this purpose. Application for a free use permit will be required if bedload material is to be excavated. For planning purposes, it is estimated that ecosystem restoration easements will need to be acquired on approximately 34 parcels from 37 landowners. For Areas 1, 4, 9 and 10, the BLM will require free use permits on 3 parcels. Additional easements for sites A-H are anticipated to have similar requirements.

Teton County is the land manager in one of the proposed restoration areas and has regulatory authority over gravel extractions. Upon initiation of the project, a comprehensive extraction permit would be sought from the County to cover all of the proposed extractions within the project scope. Plans providing the excavation details will be delivered to the Teton County Planning Office and held for review by the planning staff.

The Wyoming Department of Transportation has a maintenance easement at the Jackson-Wilson Bridge which lies within one of the proposed restoration areas. While no permits are required, an excavation plan which involves this area should be sent to the Resident Engineer for review.

d. Real Estate Requirements by Area. The following section summarizes areas and parcels within Areas 1, 4, 9 and 10, the existing easements, and what easements will be needed.

5.4.3 Summary of Real Estate Costs

The sponsor will use a non-standard channel improvement easement for ecosystem restoration, where a levee easement does not already exist or is insufficient, to obtain access and the right to install restoration features. (The sponsor will not use condemnation to obtain any easement or access). The restoration features proposed will likely benefit the properties involved. Therefore, compensation normally awarded to offset any adverse effect of a proposed activity usually requiring an easement (i.e., utilities), is insignificant in this case.

Real estate costs for Areas 1, 4, 9, and 10 are summarized in table 5.5 below. Detailed cost breakdowns are provided in appendix F, Real Estate. For planning purposes it is estimated that easement acquisition will occur at a nominal cost of $1,000 per easement for not more than 34 parcels. All costs are in 1999 dollars. Real estate costs for Areas A-H are expected to be similar and are included in the Progressive Plan cost estimates.

5.5 Transportation

Impacts upon transportation would occur as a result of construction of the environmental restoration project and subsequent performance of work to maintain the structures. Both construction and maintenance will require similar measures to implement. However, maintenance will likely involve less effort than actual construction; therefore, potential impacts from maintenance should be less than those of construction activities.

The transport of construction materials and supplies to the project areas will increase truck traffic on primary highway routes and secondary roads. Trip repetitions for this type of traffic will generally be limited; therefore, any impact upon traffic patterns from this particular truck activity is expected to be minimal.

The ingress and egress of gravel trucks between gravel screening sites and upland disposal areas at existing gravel processing facilities will likely generate the greatest traffic increase on primary and secondary roads. Because the quantity of gravel that may be transported will reasonably vary from site to site and from year to year, establishment of an estimate for the number of repetitions necessary to perform construction and maintenance is difficult. It is reasonable to expect peaks in truck traffic that will add to or create traffic congestion.

Conflicts may exist between contractors performing maintenance of the Jackson Hole Flood Control Project and contractors constructing the environmental restoration project. The Corps will address such conflicts that occur on the Jackson Hole Flood Control Project access roads and levees. The local sponsor will identify any transportation conflicts on public roads and implement traffic control measures (such as flaggers or signage) at locations that experience more than minimal increases in traffic congestion. Operation of loaded trucks on the Jackson Hole Flood Control Project levees and access roads during construction and maintenance will likely cause impacts to the surface of these structures. The Corps will ensure repair of such surface impacts resulting from construction. The local sponsor will be responsible for repairs to the surface resulting from their post-construction maintenance activities. Because surface repairs will be implemented, impacts upon the access roads and levees would be temporary.

Staging areas for fuel and lubricant storage and dispensing will be located outside of the leveed sections of the Snake River. Staging outside the levees will dramatically decrease the potential for unintentional releases of toxic materials into the Snake River. A minimum of one staging area will be necessary at each of the three working areas. Staging areas will be selected and any easements, licenses, or permits necessary for staging areas will be acquired by the local sponsor. The contractor and any subcontractors will be required to submit for approval, prior to initiation of construction, a hazardous materials spill and cleanup plan including tools and materials that will be on hand and readily available to facilitate containment and cleanup. All overnight equipment storage, as well as refueling and maintenance activities, will be restricted to staging areas. Based upon the above measures, no more than minimal, short-term impacts upon transportation are expected from either maintenance or construction of the environmental restoration project.

Access to work areas will occur primarily upon the roadways identified below, in addition to other unnamed roadways. Access will generally originate from public roadways and may use roadways already under easement for access to the levees for the purpose of performing O&M activities. Real estate instruments necessary for access will be identified in the local sponsor’s real estate report. The local sponsor will coordinate acquisition of necessary real estate instruments.

The roads for the levee access easements are typically dirt roads and are suitable for moving construction equipment. Flows in the Snake River are too high to allow for construction access from only one side of the river so access from both sides of the river will be necessary. The contractor will coordinate with the Corps’ biologist, a representative for the flood control project, and the landowner (in the field) to determine the optimum access routes for minimizing disturbances. The east and west access points for Areas 1, 4, 9 and 10 is described below. Access to areas A through H will be determined in the PED phase.

5.5.1 Area 1 Access

The west portion of Area 1 will be accessed from Fall Creek Road and involves two different access points. The first access point is for the downstream work area. The access originates off of Fall Creek Road and follows a dirt road to Sewell Levee, continuing along Sewell Levee to the work area. The access to the upstream work area originates from Fall Creek Road and follows a dirt road to the work area. This access will need to be determined in the field.

The east portion of Area 1 would be accessed from the north from South Park Loop along a 1-mile stretch of gravel road to the Lower Imenson Levee. Once on the levee, construction equipment will follow the levee until it terminates. After the levee ends, access will continue through existing shrubs and trees and over gravel bars. The contractor will coordinate with the Corps in the field to determine the optimum routes for minimizing disturbances.

5.5.2 Area 4 Access

The east portion of Area 4 will be accessed from the Federal Levee Extension. Construction equipment will leave the public highway, approximately 4 miles to the north and follow the left bank of the Federal Levee Extension to the work area. Access to the west portion of Area 4 will be from Fall Creek Road along an existing gravel road. This access crosses an existing bridge and terminates at the channel bottom. The contractor may need to navigate across gravel bars and around existing vegetation.

5.5.3 Area 9 Access

Access to the east portion of Area 9 will be from State Highway 22, which provides access to the Left Bank Federal Levee. From the Left Bank Federal Levee, an access point to the specific work areas will be selected in the field. Access for the west portion of Area 9 will originate from State Highway 390. From State Highway 390, the contractors will follow an existing dirt road to the Right Bank Federal Levee.

5.5.4 Area 10 Access

The work on the east portion of Area 10 will be reached from the downstream direction or the upstream direction. From the downstream direction, equipment will travel from State Highway 22 and then up the Left Bank Federal Levee for approximately 3 miles to the work areas. From the upstream direction, equipment will travel from Cattleman’s Bridge, which is approximately 2 miles away, to the Hanson Levee. The spur dikes located to the north will be accessed from Spring Gulch Road, which is about 2 miles away. Most of the work in Area 10 lies to the west of the river and will be accessed via the Right Bank Federal Levee. From the levee, construction equipment will traverse existing gravel bars and around or through vegetated areas to the specific work areas. Equipment could reach the levee from both the upstream and downstream directions. The downstream end of the levee will be accessed from a dirt road that runs for about three-fourths of a mile from State Highway 390 to the Right Bank Federal Levee.

5.6 Socioeconomics

The Progressive Plan is expected to yield the most benefit to the riparian and aquatic habitat. When the Progressive Plan alternatives are implemented the Corps speculates that over the 50-year project period it will help maintain the average annual fish numbers (fine-spotted cutthroat trout and other species) at their present population. Without the environmental restoration project, aquatic and riparian habitat will be expected to decline over the next 50 years. The environmental restoration project, by improving the aquatic and riparian habitat, is also expected to enhance the aesthetics of the area to visiting sports persons and tourists, in general, regardless of their objectives in visiting the Jackson Hole area. By increasing the amount of vegetation in some areas, people may have a better experience when they go fishing. Most fishermen probably would rather see trees and other vegetation than bare cobble and gravel.

Based on statistics furnished by Jackson Hole Economic Development Council Web site, local jobs maintained by the $143 million output related to sports fishing, account for about 25 percent of the total employment of Teton County. If this output and associated sales are maintained, 4,500 jobs will be enhanced in the area.

5.7 Recreation

The Snake River in the vicinity of the proposed NER project principally experiences recreational use from rafting and fishing, with some waterfowl hunting. Existing levees are used for a variety of recreational purposes including walking, hiking, jogging, bicycling, cross-country skiing, horseback riding, bird watching, nature viewing, picnicking, and other similar uses. The levees also provide access for direct river use such as fishing and waterfowl hunting. The NER Plan has the potential for both short-term and long-term impacts upon recreational uses. Recreational use could potentially be affected by construction, impacts from the presence of completed structures, and impacts from structure maintenance.

The effects of construction activity will occur principally in the form of short-term impacts. These impacts will occur during ingress and egress of equipment to the work sites and during actual on-site construction. Access to the work sites will occur over a variety of routes and for a variety of purposes. Access will be necessary to transport equipment, materials, and supplies to and from the work sites. Some routes will require use of levees and others will not. Of the levees that will be used for ingress and egress, some receive recreational use and others do not. Those that receive recreational use have the potential for user conflicts to develop.

At Area 9, the public has access to both the Right and Left Bank Federal Levees. Since these are proposed for construction access, a short-term impact is expected. In addition, access to reach the Left Bank Federal Levee on the east side will be through an existing conservation park used by recreationists, and access to the Right Bank Federal Levee will occur upon an existing unpaved road leading to a boat launch and parking area

The majority of recreation use in the project areas occurs near the Highway 22 Bridge in Areas D, 9, E, and 10, which witnesses year-round activity. Levees at Area D, 9, E, and 10 will be used in support of construction and will be clearly signed at all access points to alert users to the presence of trucks and other equipment. Because the greatest use by recreationists occurs on the Left and Right Bank Federal Levees upstream of the Jackson-Wilson Bridge at Areas D, 9, E, and 10, the greatest inconvenience upon recreationists will likely occur at these locations. A flagger would be posted, when necessary, at the Area 9 boat ramp to coordinate use between recreationists and construction equipment using the site for ingress and egress to construction areas.

Operation of equipment upon levees accessible to the public will create a conflict for persons hiking or walking the levee. As indicated above, traffic control measures, such as flaggers or signage, will be used at locations that will experience more than minimal conflicts between recreationists and construction-related activity. Such situations will be identified and resolution measures implemented by the local sponsor. Impacts from construction-related activity upon levee users will be temporary and will be minimized through the use of measures referenced above.

Gravel removal to maintain channel capacity and construct channel stabilization pools will occur in areas of the primary river channel. In-channel work may also involve construction of temporary water diversions or berms to reroute flows and de-water gravel removal sites. Spur dikes will be constructed adjacent to levees where the high-velocity flows of the primary channel occur. Rafters and float fishermen will be the primary recreationists likely to be affected by the in-channel work. Fishermen fishing from the bank or wading will be less affected. The primary effect upon rafters and float fishermen will occur from the temporary alteration of the primary channel flow. The proposed gravel removal will have only a minor effect upon rafters and float fishermen.

Presence of completed eco-fences, channel stabilization pools, anchored root wad logs, and spur dikes will change the configuration of the river channel and effect flow patterns. Eco-fences, anchored root wad logs, and spur dikes will result in more permanent changes to the channel than will the channel stabilization pools. Channel stabilization pools will trap bedload materials, therefore becoming less prominent over time. However, maintenance of the channel stabilization pools after they have filled with bedload material would result in renewed changes in configuration and flows.

Permanent changes in the channel are expected to have long-term, yet minimal impacts upon rafters and float fishermen. Rafters will have to become accustomed to the new configuration and flows resulting from spur dikes, anchored root wad logs, and eco-fences. Because these structures will not be in the middle of the primary flow, rafters and float fishermen should have little difficulty negotiating or bypassing the structures. The effort required for rafters and float fishermen to learn the new changes are expected to be no greater than is required each year after seasonal high flows. The permanent changes in configuration and flow will not de-water the channel or restrict access. The permanent changes have considerable potential to provide long-term benefits to recreational users through the creation of additional fish habitat.

If structures are damaged by high flows, parts of structures, such as cables from eco-fences, could pose a hazard to rafters and float fishermen. To alert river users to the presence of the new structures, the local sponsor will implement a public information campaign and perform monitoring and maintenance to identify potentially unsafe structure conditions.

Gravel removal to maintain channel capacity and construct channel stabilization pools is expected to have even less impact on recreationists than the eco-fences, channel stabilization pools, anchored root wad logs, and spur dikes. Channel stabilization pools will cause slower flows, creating a pool effect, therefore not posing a hazard or barrier to floaters. This change is not expected to have more than a minimal effect on rafters and float fishermen. Floaters and rafters will likely experience improved floating conditions due to stabilization of the channel. Overall, the permanent, long-term effects upon recreation resulting from the presence of the completed structures are expected to be minor.

The effects of maintenance upon recreation activities will be similar to those resulting from construction. However, work required to perform maintenance is reasonably expected to be less than would be required to actually construct the environmental restoration project. Primary effects will result from ingress and egress of equipment and actual construction activity and will be short-term.

A public information campaign will be implemented by the local sponsor to inform the recreating public about the environmental restoration project and possible conflicts between recreationists and construction activities. The campaign will include installation of appropriate signage at all levee access points and at the ramp and conservation park at Area 9. An information brochure will be prepared and distributed by the local sponsor to all fishing and rafting outfitters as well as placed at information boards at public access areas. Other sources available to the local sponsor for distributing information to the public may include the print media and radio. The campaign will be implemented both prior to and during construction.

5.8 Aesthetics

The Jackson Hole area is popular as a year-around recreation destination. The area’s spectacular scenery is of national significance, as evidenced by the establishment of the Grand Teton National Park in 1929. The proposed environmental restoration project areas are located in the outwash plain of the Snake River. The river channel is relatively wide and braided with extensive areas of gravel bars. Riparian vegetation is found along many of the channels. Stands of trees, composed primarily of cottonwoods, willow, and alder are scattered throughout the outwash plain. Views of the floodplain, by boaters and other recreationists using the Snake River, are generally restricted because of adjacent riverbanks, levees, and vegetation. The primary views along the rivers are of the mountains, particularly the Grand Teton Mountains, which can be viewed beyond the riverbanks and levees in locations where there are openings in the riparian vegetation.

Since the mid-1990’s, Area 1 has undergone extensive lateral erosion due to the "firehose" effect of concentrated river flows emerging from the confined channel upstream. The installation of eco-fences and anchored root wads will help to reestablish island vegetation as well as help to reestablish island vegetation as well as help protect existing islands and encourage growth of new islands.

The vegetation at Area 4 is predominately shrub-willow. Most of the existing islands currently within the channel are devoid of vegetation due to island instability and changing river flows. The installation of eco-fences and anchored root wad logs will help reestablish island vegetation.

The river at Area 9 is somewhat restricted and the islands are devoid of vegetation. The vegetation along the shoreline is predominantly shrub-willow. Rock grade control structures will be constructed flush with the existing channel bottom and will help prevent bank erosion and degradation of existing habitat. Eco-fences and anchored root wad logs will assist in revegetation of existing islands and establishment of new islands. Spur dikes will be used to provide bank protection and enhance fisheries habitat by creating flow diversity and enhancing pools, fish resting areas and riffles, thus improving the visual quality of the riverbanks.

Area 10 is located at the confluence of the Gros Ventre and Snake Rivers. This area has extensive cottonwood vegetation on existing islands and along the shoreline. Eco-fences and anchored root wad logs will assist in promoting a more diverse vegetative cover along existing shorelines and encourage the growth of new islands. Spur dikes will enhance fish habitat and provide additional bank protection. This will allow regeneration of native plants as well as improve the visual quality of the riverbanks.

The removal of gravel to maintain channel capacity and construct channel stabilization pools and the presence of the anchored root wad logs, eco-fences, off-channel pools, and secondary channels are not expected to contrast sharply with the existing surroundings. The proposed measures are expected to create long-term potential for restoring aquatic and terrestrial habitat along the environmental restoration project area. Over time, with the reestablishment of islands and vegetation, the aesthetics of the project area would improve.

During construction stockpiled gravel, screened cobble, and discharged riprap for eco-fences, spur dikes, and rock grade control will contrast with the surroundings however, stockpiling of gravel and screened cobble may not occur. If it does, visual impacts would be temporary because the material will only be in place a short period of time. Accumulation of woody debris on the piling and rock eco-fences will cause their visual contrast to be short-term. Rock grade control will be unobtrusive due to the embeddedness of the material. Contrast of the spur dikes to existing surroundings will be evident to rafters and float fishermen traveling the river and to persons visiting areas that are publicly accessible. Anchored root wad logs will blend in with the setting.

5.9 Cultural Resources

A copy of the Corps’ Survey Report was forwarded to the Wyoming Division of Cultural Resources, State Historic Preservation Office, for review and concurrence. In their letter of February 12, 1997, the SHPO responded that no sites meeting the criteria of eligibility for the National Register of Historic Places will be affected by the environmental restoration project. The SHPO recommended the project proceed in accordance with state and Federal laws, subject to the following stipulation: "If any cultural materials are discovered during construction, work in the area should halt immediately and the Corps and SHPO staff must be contacted. Work in the area may not resume until the materials have been evaluated and adequate measures for their protection have been taken." Refer to appendix H, Environmental Assessment, which contains appendix D for the SHPO letter concurring with the Corps’ determination of "no effect" for areas 1, 4, 9, and 10. Additional coordination may be needed for areas A-H which will be conducted during the PED phase.

5.10 Cumulative Effects

The Flood Control Act of 1950 authorized flood protection by levees and revetment along the Snake River in the Jackson Hole, Wyoming area. The project was completed in the fall of 1964. Levees have been added to the system by other agencies and by emergency flood fight operations of the Corps and Teton County through 1997. The effect of these measures has been the alteration of the physical character of the river, both inside and outside of the levees, along approximately 25 miles between Moose Bridge and South Park National Elk Feedgrounds. Presently, the following effects have been observed:

• The width of the Snake River floodplain is reduced by the levees.
• Flow velocities through the leveed sections are increased.
• Elevated quantities of bedload material is transported through the area.
• Islands and associated vegetation is eroding.
• Water flows to spring creeks outside of the levees have been reduced.
• Spawning habitat for fine-spotted cutthroat trout has been reduced or destroyed.
• The composition and quality of riparian vegetation outside of the levees is changing.

According to the best information currently available, the implementation of these type of restoration tools in various locations of this 22-mile project is anticipated to have long-term beneficial effects on water quality, recreation, and habitat for aquatic and terrestrial species. No long-term adverse cumulative effects are predictable.

The Progressive Plan of this project includes an important and innovative element for addressing cumulative effects, that is, adaptive management. This allows cumulative effects to not only be analyzed now, but also reevaluated for each subsequent construction effort. Since the river dynamics are constantly changing the environment, adaptive management is an excellent way to address current and future cumulative effects, positive and negative. This type of progressive planning and analysis requires that the traditional one-time cumulative analysis be expanded to an ongoing effort. Adaptive management, by implementing detailed, specific analysis and monitoring of each site location, as it is added, allows for continuing confirmation that project actions are beneficial.

The next paragraphs briefly summarize the current cumulative aspects of the first four sites.

Environmental restoration measures proposed for Area 1 include excavation of a single channel stabilization pool and four off-channel pools with connecting upstream and downstream secondary channels, construction of eco-fences, and placement of anchored root wad logs. Construction will result in minor, nonbeneficial short-term impacts to water quality, air quality, aesthetics, recreation, aquatic and terrestrial species and habitat, and local transportation. Presence of the completed structures will have long-term beneficial effects upon water quality, recreation, and aquatic and terrestrial species and habitat.

Environmental restoration measures in Area 4 will include: excavation of two channel stabilization pools and three off-channel pools with connecting upstream and downstream secondary channels; construction of eco-fences and spur dikes; placement of anchored root wad logs; and removal of gravel to maintain channel flow capacity within 100-year event flows. Construction will result in minor, nonbeneficial short-term impacts to water quality, air quality, aesthetics, recreation, aquatic and terrestrial species and habitat, and local transportation. The completed structures will cause long-term beneficial effects upon water quality, recreation, and aquatic and terrestrial species and habitat by stabilizing the channel and allowing recovery of aquatic and terrestrial habitat. Actions proposed in Area 4 will not add to the cumulative adverse effects caused by previous flood control actions at Area 4.

Environmental restoration measures in Area 9 will include: construction of eco-fences, spur dikes, placement of anchored root wad logs, and removal of gravel to maintain channel flow capacity within 100-year event flows. Construction will result in minor, nonbeneficial short-term impacts to water quality, air quality, aesthetics, recreation, aquatic and terrestrial species and habitat, and local transportation. Presence of the completed structures in Area 9 will result in long-term beneficial effects upon water quality, recreation, and aquatic and terrestrial species and habitat. The changes attributable to the collective effect of actions proposed for Area 9 will decrease nonbeneficial effects of past flood control activities and cause an overall net increase in beneficial effects in the long-term. No measurable increases in the net detrimental effects caused by previous flood control activities will occur.

Environmental restoration measures in Area 10 will involve excavation of a single channel stabilization pool and two off-channel pools with connecting upstream and downstream secondary channels, construction of eco-fences, placement of anchored root wad logs, spur dikes, and removal of gravel to maintain channel flow capacity within 100-year event flows. Construction in Area 10 will also cause minor, nonbeneficial short-term impacts to water quality, air quality, aesthetics, recreation, aquatic and terrestrial species and habitat, and local transportation. Water quality, recreation and aquatic and terrestrial habitat will benefit in the long-term from the presence of the completed structures. Changes caused by the cumulative effect of actions proposed for Area 10 will cause the nonbeneficial effects from past flood control activities to diminish. In the long-term, an overall net beneficial increase in aquatic and terrestrial habitat will occur.

Environmental restoration measures in Areas A through H will have similar effects as those anticipated for Areas 1, 4, 9, and 10. The cumulative effect for restoration of the entire 22-mile reach of the Snake River from Teton National Park to the South Park Elk Feedgrounds is significantly greater than result of restoring one or more of the individual areas identified in this Study.

The cumulative effect of past and proposed actions along the Snake River will not cause additional reduction in the width of the floodplain, increase flow velocities through the levied areas, increase transport of bedload material, destabilize the channel, erode islands and vegetation between the levees, or diminished flows to spring creeks outside of the levees. The cumulative effect of the proposed environmental restoration project will be improved water quality through reduced velocities and stabilization of the channel, reduced erosion of islands and loss of vegetation, opportunity for the reestablishment of islands and vegetation, and creation of additional habitat for fine-spotted cutthroat trout and other aquatic and terrestrial species.

5.11 Project Performance

The paragraphs below describe the expected performance and effectiveness of each project element within the restoration areas, and the impacts to areas downstream of the proposed projects.

5.11.1 Eco-Fences

Fence structures of various designs have been tested for use as bank protection or river training structures. A number of these designs and case histories are described in the December 1981 U.S. Army Corps of Engineers Publication, Final Report to Congress: The Streambank Erosion Control Evaluation and Demonstration Act of 1974, Section 32, PL 93-251. In some cases, particularly in meandering streams where the flow velocities were low, they have proved effective in collecting sediment and stabilizing the channel. The effectiveness of fences in braided channels with high-velocity flow is much less certain.

The effectiveness of the fences will depend, to a large degree, on the amount of floating debris available in the river and actually trapped against the fences. In order to be effec-tive, the fences must trap enough debris to uniformly block most of the flow along the length of the fence. If too little accumulates, the current may pass through the fence with little or no velocity attenuation. An upstream fence may trap most of the available debris, reducing the supply to downstream fences. Depending on the angle of attack, floating debris may be deflected and fail to become trapped against the fences. There is also a risk that excessive flow may escape under floating debris, or erode a path under the fence below the lowest cross-cables.

Failure of some fence projects in other locations has resulted from insufficient depth of supporting posts, breakage, or an alignment that allowed the flow to bypass or flow behind the fence. At impingement points, velocities of 12 fps (or even higher) have been measured during peak flows. The end of the fence extending out into the channel will be exposed to the greatest stress. There will be erosion around the toe, force fluctuations resulting from debris striking the fence or shifting position, and vibration caused by vortex shedding. In the most severe case, erosion may extend to a depth of up to 15 feet below the water surface. Debris may not collect effectively at the end of the fence leaving the fence exposed at this location. Since undercutting is likely to be the worst at the end of the fence, experience may dictate the need to extend cross-cables and wire mesh to a greater depth at this location.

The need for a minimal level of maintenance cannot be overemphasized. The visual impact of the fences could become a major consideration. The fences will create a scalloped pattern of vegetation and debris, with the tips of the fences forming the points. Insufficient debris may leave the tip of the fence or other portions of the structure exposed. With no maintenance, a failed fence could become an eyesore and a possible hazard with partially-buried woody debris mixed with a tangle of steel posts and cables strung out downstream of the original construction site.

The number and extent of river training structures is not sufficient to assure that the river cannot escape and follow an undesirable alignment. The river will change course frequently and may, for a time, completely abandon the spur dikes, fences, and other restoration features.

5.11.2 Secondary Channels

It should be assumed that most of the small secondary channels leading to off-channel pools will be blocked by gravel at their upper ends after each runoff season. Although groundwater seepage will provide some flow, it should be assumed that most of channels will have to be re-opened each season in order to provide an optimum exchange of water for the downstream pools. Starting at the edge of the main channel, a small connecting channel will be extended downstream or the existing channel will be deepened until a flow of 2 to 3 cfs was developed in the channel leading to the pool.

In some areas sufficient flow may be developed from groundwater seepage without actually having to connect the channel to the main river. The channel-excavation would typically be around 4 feet wide at the bottom, 200 feet long, and 3 feet deep. A backhoe would typically be used to excavate the channels. Where possible, particularly in vegetated areas, it will be desirable to remove the excavated gravel. However, in may cases the amount of material will be small or the location inaccessible, and less disturbance will be involved if material were side-cast and graded to blend with the surrounding terrain.

The secondary, supply channels will have little effect on the overall hyd-raulics of the system. Hydraulically, these channels will be successful if they survive through successive high-flow peri-ods without excessive maintenance. However, the channels will not be useful if the substrate and flow-regime does not contribute to improved habitat.

5.11.3 Channel Stabilization Pools

Since the supply of sediment being transported downstream is not precisely known and may vary by at least an order of magnitude between years, the optimum size and effectiveness of the sediment traps is not known. Gravel removal will need to be closely controlled and its effects monitored. Removal of more gravel than is being re-supplied will result in progressive lowering of the channel bed within the designated sediment trap boundaries, excessive headcutting upstream, and excessive channel entrenchment downstream. This could lead to a local depression of the water table, and undercutting of the toe of the riprap on nearby levees.

During the coldest winter months of November-February, the potential for ice blockage of the active, low-flow channel will be increased in vicinity of the gravel trapping areas. The low-flow channel may be frozen clear across at times with part of the flow passing under the ice cover and the remaining flow backing up and overflowing into secondary channels that would normally be dry at this time of the year. Since the distance between the levees is several times the width of the low-flow channel, and there is no development immediately adjacent to the low-flow channel in other areas, this condition is not expected to create any increased risk of flooding or other serious prob-lems.

5.11.4 Off-Channel Pools

Depending on the location and the timing of high flows, pools could be refilled with gravel and cobbles and totally eliminated before they have existed long enough to perform a useful role. In the worst case, some of the pools may be eliminated by the next high flow after construction. Pools in most areas will be subject to refilling during high-flow seasons. If this process occurs over a period of time it can actually be beneficial, since it will provide a controlled sequence of differing plant communities and provide more diverse habitat. In some locations the pools may serve a dual role as habitat providers and sediment traps. Those located some distance from the main channel will likely last a number of years. They will gradually refill with silt and sand brought in by the interconnecting channels, and by general overbank flow during high-flow periods. Due to the braided nature of the river, it is nearly impossible to select locations where pools will be subjected to a predictable level of protection from flood events. An additional potential problem is isolation of the pool and entrapment of fish during low-flow periods due to excessive seepage into the gravel bed or banks of the pool. Freezing of the pools and secondary channels during the winter may also be a consideration.

5.11.5 Spur Dikes

Spur dikes will occasionally be damaged by high flows. Measurements at various locations on the existing channel in-dicate that erosion can extend down to at least 15 feet below the high-water level. It would not be practical to construct the dikes with large enough stone and with a deep enough toe to avoid any possibility of damage. The mode of damage will likely be undercutting of the toe of the dike and collapse of material into the void with some material being transported downstream. Repair will involve adding enough riprap to restore the original geometry.

5.11.6 Effects of Alternatives on Existing Hydraulic Conditions

At Area 1, the NER Plan includes channel excavation, eco-fences, sediment traps, spur dikes, side pools, anchored woody debris, supply channels, and a modest shortening of the channel. No rises in the 100-year water surface are expected as a result of the restoration measures. The model shows lower water-surface elevations up to about 1 ft in the excavated areas. Localized rises upstream of the channel restoration work are results of extrapolation inaccuracies. Fence structures are to be located in previously vegetated areas. The gravel removal and channel shortening should shift the river regime slightly toward channel entrenchment, increasing channel stability and reducing the risk of flooding and erosion.

At Area 4, the NER Plan includes channel excavation, eco-fences, sediment traps, spur dikes, side pools, anchored woody debris, and supply channels. As documented in appendix B, Hydrology, the 100-year water-surface elevations are lowered as a result of the project (plate 34). Average channel velocities for all events (10-, 50-, 100-, and 500-year and 1997 historical flood) are generally higher in the restored condition and reflect increased efficiency due to the channelization components.

At Area 9, the NER Plan includes channel excavation, eco-fences, side pools, staggered log protection, anchored woody debris, spur dikes, grade control, and supply channels. The 100-year water with-project surface elevations are generally less than or equal to the existing water-surface elevations throughout the restoration area (plate 35). (Note: The rise in water-surface elevation shown at cross section 13 on plate 35 is due to a mathematical anomaly in the profile and not to any physical change in the river.) The with-project average channel velocities are considerably lower in the downstream portion of the area, but are equal to or higher than the existing velocities in the upper section.

At Area 10, the NER Plan includes channel excavation, eco-fences, sediment traps, side pools, spur dikes, anchored woody debris, and supply channels. The 100-year water with-project surface elevations are generally lower in the downstream portion of restoration area, but are somewhat higher (on the order of 1 foot) in the upstream portion (plate 36). However throughout the entire site, the with-project profile is lower than the 1973 Flood Insurance Study (FIS) profile. The with-project average channel velocities were somewhat lower (but almost equal) in the downstream portion of the area but were generally higher in the upstream portion.

Area A through H effects will be determined during the PED phase. The features will be designed to the same standards as Areas 1, 4, 9, and 10. The project flood profile will be lower than the 1973 Flood Insurance Study profile.

5.11.7 Downstream Impacts

Downstream impacts from the proposed restoration projects are minimal. In terms of flood control, the proposed changes to the low-flow channels and installation of sediment traps only affect the project area and do not affect downstream water-surface elevations or velocities (see tables 7 through 9 and 11 through 13 in appendix B, Hydrology). In terms of levee maintenance, the restoration alternatives will tend to guide low flows away from the banks and levees and toward the center of the river, and will reduce impingement on the levees and the associated erosion in the immediate downstream vicinity of the project. However, given high bedload of the system and the random nature of the low-flow channel morphology between the levees, the river training effects of the restoration measures will not carry forward downstream of the project areas for any appreciable distance.

The development of all areas identified in the Progressive Plan will have a stabilizing effect on the entire reach from Teton National Park to the South Park Elk Feedgrounds. The Progressive Plan is expected to provide restoration to important natural resources and reduce flood control maintenance requirements.

5.12 Coordination with other Regional Restoration Initiatives

The focus of this project will extend beyond its physical improvements. The community, local interest groups, and property owners have indicated their support for this project and their desire to create additional restoration opportunities. Currently local interests are considering a Section 1135 project to restore flows behind or landward of the levees for restoration of spawning habitats. The intent of the flood control project modification study (Section 1135) will be to restore spring creek and wetland values. The Teton County Conservation District, along with the WGFD, Trout Unlimited and the National Fish and Wildlife Foundation, are expending additional efforts in restoring riparian and spring creek habitats behind the levees. This study and the resulting construction will further stimulate local, regional, and natural restoration interests. The overall goal of the supporting interests of this project is to create a long-term cultural shift toward the natural management of these important sustainable resources.

6. PLAN IMPLEMENTATION

This chapter summarizes cost-sharing requirements and procedures necessary to implement the environmental restoration features of the proposed NER Plan.

In addition to and as part of project authorization, the local sponsor is seeking legislative language which will provide the local sponsor with a credit for "in-kind services" to be performed by the local sponsor during construction phase and a credit for previous funds paid during project design. This credit would be available as against the local sponsor's obligation to fund 35 percent of project construction costs. Thus, the local sponsor's ability to finance 35 percent of the project's construction cost is contingent upon its success in obtaining the requested legislative language. If the required legislation is provided, analysis of in-kind services available for performance by the local sponsor, together with credit for prior funds paid, reveals that the local sponsor will be capable of meeting its responsibility to fund 35 percent of construction costs.

6.1 Progressive NER Plan

The identified Progressive Plan provides the maximum National Ecosystem Restoration (NER) benefits. Because of its positive contributions to improving the environmental values within the Jackson Hole study area, Alternative A3+B3+C3+D3 (50-year piling eco-fence designs and other features as described in section 5 at Areas 1, 4, 9, 10 and A through H) is recommended for implementation.

6.2 Division of Responsibilities for Implementing Recommended Plan

The WRDA 86 and various administrative policies have established the basis for the division of Federal and non-Federal responsibilities in the construction, maintenance, and operation of Federal water resource projects accomplished under direction of the Corps. Anticipated Federal and non-Federal responsibilities are described in this section. The final division of specific responsibilities will be formalized in the project cooperation agreement (PCA).

6.2.1 Federal Responsibilities

The estimated Federal share of the total first cost of the project is 65 percent of first costs [first costs are all costs to implement project less lands, easements, rights-of-way, relocations, and disposals (LERRD) and O&M costs]. The Federal government responsibilities are anticipated to be:

a. Design and prepare detailed plans and specifications.

b. Administer contracts for construction and supervision of the project after authorization, funding, and receipt of non-Federal assurances.

c. Conduct all necessary cultural resource investigations and coordinate and implement any necessary preservation or mitigation measures.

d. Conduct periodic inspections with the non-Federal sponsor to determine adherence to the post-construction maintenance requirements

e. Identify the real estate needs for implementation of environmental work on Federal and private land.

6.2.2 Non-Federal Responsibilities

Non-Federal or local responsibilities are anticipated to be:

a. Provide 35 percent of the project implemenation costs (preconstruction, engineering, and design, and construction) in keeping with current Corps of Engineers’ policy as further specified below:

b. For so long as the project remains authorized, operate, maintain, repair, replace, and rehabilitate the completed project, or functional portion of the project, at no cost to the Government, in accordance with applicable Federal and State laws and any specific directions prescribed by the Government.

c. Give the Government a right to enter, at reasonable times and in a reasonable manner, upon land, which the local sponsor owns or controls for access to the project for the purpose of inspection, and, if necessary, for the purpose of completing, operating, maintaining, repairing, replacing, or rehabilitating the project.

d. Assume responsibility for OMRR&R for the project or completed functional portions of the project, including mitigation features without cost to the Government, in a manner compatible with the project’s authorized purpose and in accordance with applicable Federal and State laws and specific directions prescribed by the Government in the OMRR&R manual and any subsequent amendments thereto.

e. Enter into a PCA prior to start of construction in compliance with Section 221 of the Flood Control Act of 1970 (PL 91-611), as amended, and Section 103 of the WRDA 86, as amended, which provides that the Secretary of the Army shall not commence the construction of any water resources project or separable clement thereof, until the non-Federal sponsor has entered into a written agreement to furnish its required cooperation for the project or separable element.

f. Hold and save the Government free from all damages arising for the construction, operation, maintenance, repair, replacement, and rehabilitation of the project and any project-related betterment’s, except for damages due to the fault or negligence of the Government or the Government's contractors.

g. Keep and maintain books, records, documents, and other evidence pertaining to costs and expenses incurred pursuant to the project to the extent and in such detail as will properly reflect total project costs.

h. Perform, or cause to be performed, any investigations for hazardous substances that are determined necessary to identify the existence and extent of any hazardous substances regulated under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), 42 USC 9601-9675, that may exist in, on, or under lands, easements or rights-of-way necessary for the construction, operation, and maintenance of the project; except that the non-Federal sponsor shall not perform such investigations on lands, easements, or rights-of-way that the Government determines to be subject to the navigation servitude without prior specific written direction by the Government.

i. Assume complete financial responsibility for all necessary cleanup and response costs of any CERCLA regulated materials located in, on, or under lands, easements, or rights-of-way that the Government determines necessary for the construction, operation, or maintenance of the project.

j. To the maximum extent practicable, operate, maintain, repair, replace, and rehabilitate the project in a manner that will not cause liability to arise under CERCLA.

k. Prevent future encroachments on project lands, easements, and rights-of-way, which might interfere with the proper functioning of the project.

l. Comply with the applicable provisions of the Uniform Relocation Assistance and Real Property Acquisition Policies Act of 1970 (PL 91-646), as amended by Title IV of the Surface Transportation and Uniform Relocation Assistance Act of 1987 (PL 100-17), and the Uniform Regulations contained in 49 CFR part 24, in acquiring lands, easements, and rights-of-way, and performing relocations for construction, operation, and maintenance of the project, and inform all affected persons of applicable benefits, policies, and procedures in connection with said act.

m. Comply with all applicable Federal and State laws and regulations, including Section 601 of the Civil Rights Act of 1964 (PL 88-352), and Department of Defense Directive 5500.11 issued pursuant thereto, as well as Army Regulation 600-7, Nondiscrimination on the Basis of Handicap in Programs and Activities Assisted or Conducted by the Department of the Army.

n. Provide 35 percent of that portion of total cultural resource preservation mitigation and data recovery costs attributable to environmental restoration that are in excess of 1 percent of the total amount authorized to be appropriated for environmental restoration.

o. Not use Federal funds to meet the non-Federal sponsor’s share of total project costs unless the Federal granting agency verifies in writing that the expenditure of such funds is authorized.

p. Enter into a PED agreement.

6.3 Preconstruction Engineering and Design Phase

The PED phase will follow the Feasibility Study. The purpose of this phase is to complete all of the detailed, technical studies and design needed to begin construction of the Jackson Hole Environmental Restoration Project. This phase ends with the completion of the first detailed construction drawings and specifications (often called plans and specs, or P&S).

Preconstruction, engineering and design will be cost shared between the Corps and the sponsor in the same proportions as the project's construction cost (65 percent Federal and 35 percent non-Federal). The major documents prepared during this phase will be the updated Real Estate Plan (REP); the PED agreement, which will include the results of advanced technical engineering studies and design; the P&S, which are the detailed drawings and instructions for building the project; the environmental compliance coordination documentation; necessary permits for removal of gravel from BLM administered lands; and the PCA, which describes the sponsor and Corps responsibilities for project construction, operation and maintenance.

Key events during the PED phase will include:

• Begin the PED phase when the Walla Walla District receives funds.
• Update REP.
• Approve PED agreement.
• Approve P&S.
• Acquire BLM permit, if required.
• Prepare PCA.

6.4 Construction Phase

The construction phase will begin after Congress appropriates funds specifically for the initiation of construction of the Jackson Hole, Wyoming, Environmental Restoration Project and these funds are allotted to the Walla Walla District. The project cooperation agreement will then be signed after Congress appropriates funds for construction. Formal notification for the sponsor to proceed with real estate acquisitions will occur after the PCA is signed.

Construction work at the project site will begin soon after the PCA is approved and executed, the real estate easements are acquired, and a construction contract is awarded.

Two major documents are also prepared during this phase: the construction contract, which is the agreement between the Corps and the contractor(s) about how the project will be built, and the project operation and maintenance (O&M) manual, which specifies the instructions for the sponsor to follow for project use after construction is finished. In addition, National Environmental Policy Review for Areas A through H will occur.

Key events during the construction phase will include:

• Appropriation of construction funds.
• PCA approval and execution.
• Construction contract advertised.
• Construction contract awarded.
• Phased construction of restoration features initiated.
• Approval of operation and maintenance manual.
• Construction completion.
• Project acceptance and transfer to sponsor.

6.5 Construction Phasing

The twelve recommended restoration areas constitute the entire project, and from a construction standpoint, can be considered as independent projects. If all 12 of the areas are implemented, construction will require 15 years for completion. The first area will require six years to complete, followed by the second area, requiring 5 years, the third area 4 years, and all remaining areas 3 years. Construction can be initiated at one or more site each year. Each area will be monitored for physical and environmental performance following completion of construction for the affected area. It is recommended that work begin on Area 9 first, and then proceed through Areas 9, 1, 4, 10, B, D, F, A, G, H, C and E. Socioeconomic and environmental factors, as well as changes in the river channel, may modify the priorities and require a change in the order of construction.

The Snake River at Jackson, Wyoming is located within a glacial outwash plain as described in the report. Due to the high sediment load, the general steepness of the valley, the high annual variation in the spring snowmelt, along with a limited construction season, the U.S. Army Corps of Engineers, Walla Walla District has determined that an expanded construction schedule is the most prudent approach to construction within this ecosystem. At each of the 12 project sites the majority of the construction would be accomplished in the first year, and continuing construction would be accomplished over the next 2 to 5 years. While in most cases this approach would be considered to be adaptive management or the operation and maintenance responsibilities of the sponsor, the report provides a convincing argument that stabilization of the channel and project features in this highly dynamic system will require continuing construction.

Rock barbs and off-channel pools may be constructed at any time during the construction year, if groundwater conditions and environmental requirements are met. However, channel capacity excavation and eco-fences must perform as a completed unit during the high-flow period. In order to maintain adequate conveyance, priority will be placed on completion of the channel excavation. In no event will the eco-fences be completed prior to completion of the excavation in an adjacent channel. Channel excavation, replacement of oversize material, removal of stockpiled gravel from the active channel area and construction of eco-fences will be completed prior to the beginning of the spring runoff period. Most construction is likely to occur during the low-flow period and during moderate weather. Gravel extraction will be more difficult, fence piling will be hard to drive, and soil cannot be effectively replaced and compacted at the fence tie-off points when the ground is frozen.

6.6 Project Monitoring Phase

A Monitoring Plan has been developed to address projection effectiveness. Monitoring will address the project objectives and determine project effectiveness. Adjustments ("fine-tuning") to the project may be undertaken in the field to correct any deficiencies that are limiting factors for ecosystem restoration benefits. The monitoring program will be no longer than the construction phase of the project. The cost associated with this activity will be cost-shared with the local sponsor in accordance with the cost-sharing requirements specified for project implementation and is included in the project construction costs.

6.7 Operation and Maintenance Phase

Following completion of the monitoring period at each site, all responsibility for ongoing project operation and maintenance including repair, rehabilitation, and major replacement will be turned over to the sponsor. The sponsor’s responsibilities in this phase also include final certification of all necessary real estate and permit requirements for completion of project O&M. Detailed O&M requirements will be specified in the project O&M manual to be developed during the PED and Construction Phases of the project. All O&M requirements in this phase are funded 100 percent by the sponsor. O&M activities for the project include maintenance of eco-fences, secondary channels, and channel stabilization pools. Anticipated O&M requirements are discussed in section 5.3.2, Project Maintenance.

6.8 O&M Efficiencies for Flood Control Projects from Environmental Project

The removal of gravel to create and stabilize channels and the construction of spur dikes and eco-fences is expected to reduce the cost of maintaining the existing flood protection project. This will be accomplished by directing flows away from levees and stabilizing the river within certain limitations, which will reduce impinging flows. Impinging flows are channel shifts that direct the flows directly against levees. When this occurs, the velocity of the flow often exceeds 12 feet per second, and may remove the protective layer of rip rap from the levee. Removing the rip rap from the levee face exposes the gravel cobble core to rapid erosion and failure.

By stabilizing channel movement throughout the restoration project impinging flows are less likely to occur. One of the tools used in environmental restoration are spur dikes. Spur dikes, as discussed in this report, extend perpendicularly or at a slight up or down angle (depending upon the specific design) deflecting the flow and reducing the energy impacting the levee. Spur dikes will be constructed in the environmental restoration project to create and enhance fisheries habitats. A secondary benefit of spur dikes is reduced levee maintenance. It is envisioned that the final location of the spur dikes will be a joint effort of the Corps, Emergency Management Branch and Teton County. Spur dikes will be located in high-energy locations where they provide levee maintenance benefits and fisheries habitat.

6.9 Cost Allocation

Cost allocation is the practice of allocating the separable costs of a project to the project purpose that they serve. For this project, all costs have been allocated to the purpose of NER.

6.10 Cost Apportionment

Cost sharing for construction of this project will be in keeping within current Corps of Engineers policy whereby for environmental restoration projects, the non-Federal share will be 35 percent of the project implementation costs (pre-construction engineering and design, and construction). Non-Federal sponsors shall provide 100 percent of LERRDs, and OMRR&R. The value of LERRD shall be included in the non-Federal 35 percent share. Where LERRD exceeds the non-Federal sponsor’s 35 percent share, the sponsor will be reimbursed for the value of LERRD that exceeds the 35 percent non-Federal share. After appropriate accounting for LERRD and required non-Federal sponsor project coordination activities under the terms of the Design Agreement and the Project Cooperation Agreement, any balance of the non-Federal share will be provided in cash during construction. Table 6.1 below provides a summary of the cost apportionment between the Federal and non-Federal interests for the Initially Proposed NER Plan.

6.11 Completed, Current, and Future Work Eligible for Credit

There is no completed work, current or planned future work that is eligible for credit under existing Corps policy. However, the non-Federal sponsor has completed during the course of the feasibility phase, advance restoration measures that are consistent with the recommended Federal plan, providing valuable information regarding the effectiveness and viability of the proposed project elements. The costs associated with the measures that have been implemented in advance by the local sponsor are not included as part of the overall project cost. Legislation is being pursued to allow in-kind service credit for construction costs.

6.12 Institutional Requirements

Before an agreement is signed for Federal construction of the cost-shared project, the local sponsor will prepare the following financial analysis:

• The local sponsor’s project-related yearly cash flows (both expenditures and receipts where cost recovery occurs), including provisions for major rehabilitation and operational contingencies and anticipated, but uncertain repair costs resulting from damages from natural events.
• The local sponsor’s current and projected ability to finance its share of the project cost and to carry out project implementation operation, maintenance, and repair/rehabilitation responsibilities.
• The means for raising additional non-Federal financial resources including but not limited to special assessment districts.
• The steps that the local sponsor will take to ensure it will be prepared to execute its project-related responsibilities at the time of project implementation.

In addition, as part of any Project Cost Sharing Agreement, the local sponsor will be required to undertake to save and hold harmless the Federal government against all claims related to environmental restoration, and other activities, associated with this project.

6.13 Environmental Requirements and Regulatory Permitting

The Initially Proposed NER Plan would result in the discharge of fill material into waters of the United states during the period of construction. It also may result in longer-term discharges associated with O&M activities. A Section 404(b)(1) evaluation was prepared to address Clean Water Act issues and a 401 Certificate was obtained from the Wyoming Department of Environmental Quality for Areas 1, 4, 9, and 10. Additional coordination will be completed on the original four sites to assure up to date compliance. Compliance coordination and documentation will be completed on the additional eight sites during the engineering and design phase. Applicable local or state permits are the requirement of the local sponsor.

In the Alternative Formulation Briefing held July 1999 in Portland Oregon, the sponsor and local interests expressed an interest in private individuals being able to use the tools developed in this study. The Corps (Walla Walla and Omaha Districts) will request funding to explore the development of regional permits under Section 404 of the Clean Water Act. Regional permit development efforts could begin in FY 00 during the Planning, Engineering, and Design phases of this project. The Corps hopes to develop criteria so that the tools developed in this study (channel creation; spur dikes; eco-fences; anchored woody debris; and secondary pools and channels) may be used by private individuals. Criteria (materials, designs, hydrologic functions, and biological functions) will be available for the individual use of these tools and for the combined use of various tools under specific physical and biological conditions. Public and agency input is considered in the development of regional permits.

6.14 Sponsorship Agreements

The local sponsor (Teton County) has provided a Letter of Intent acknowledging sponsorship requirements of the Jackson Hole, Wyoming, Environmental Restoration Project. The letter was provided June 21, 2000, following the development of a memorandum of understanding with Teton Conservation District. Prior to the start of construction, the local sponsor will be required to enter into a Project Cooperation Agreement (PCA) with the Federal Government that it will comply with Section 221 of the Flood Control Act of 1970 (PL 91-611), and Section 103 of WRDA 86.

The Corps and Sponsor believe that a single or less than 12 separate PCA’s may provide benefits (efficiencies). For example, multiple PCA’s would have to compete with other new-start projects for funding on an annual basis, and, unless delegation authority is granted, each PCA may have to be signed by the Assistant Secretary of the Army, Civil Works.

It is envisioned that as construction and the benefits of environmental restoration are realized, public awareness will build and investment interests by future partners would develop. Additional cost-sharing sponsors will enable Teton County to accelerate the phased construction schedule and increase the environmental restoration benefit yield. The Sponsor has a partnership agreement with Teton Conservation District to participate in cost sharing. The National Fish and Wildlife Foundation has participated with Teton County in building a demonstration project (see section 9.1 of this report) and has expressed interest in continuing financial participation in the project. Other organizations, such as Trout Unlimited, have pledged support for this project. As interest mounts and public recognition of ecosystem restoration benefits and costs become more firmly established, financial support by partners may allow the Sponsor to enter into a cooperative agreement to accelerate the phased construction schedule. This would accelerate the project’s NER outputs and lead to greater habitat recovery efficiencies.

7. SUMMARY OF COORDINATION, PUBLIC VIEWS, AND COMMENTS

7.1 Non-Federal Views and Preferences

The non-Federal views and preferences regarding environmental restoration measures, and the problems they addressed, in general were obtained through coordination with the local sponsor and with the other various local and regional public agencies, community activists, resource conservation groups, and the general public. These coordination efforts consisted of a series of public meetings held during the reconnaissance and feasibility phases, through surveys, through the maintenance of a point-of-contact that any interest could discuss matters with, and a mailing list by which invitations to public meetings were distributed. Announcement of public meetings was made in local newspapers, giving date, time, place, and subject matter.

7.2 Views of the Non-Federal Sponsor

The sponsors, Teton County and the Teton County Conservation District have provided a strong partnership with the Corps throughout the study. Fifty percent of the overall requirements of the study (25 percent cash and 25 percent in-kind work) were contributed by the sponsor. In-kind products such as real estate were complex tasks were performed professionally, in coordination with property owners and local interests, and internally coordinated with Corps staff. The sponsor(s) have indicated their willingness to continue support during the project’s implementation phase. In October 1998, the sponsor(s), with Corps over-sight and assistance embarked on a demonstration project that is representative of some of the key elements found in the Corps’ Initially Proposed NER Plan. The demonstration project was funded by Teton County, in cooperation with Teton Conservation District, a private contractor, and the National Fish and Wildlife Foundation. The demonstration project was completed in 1 year and is being monitored. The supplementary section at the end of this report includes a document (Final Report: Snake River Restoration Demonstration Project, by Teton Conservation District) and an article ("The Good Flood" from the Ingersoll-Rand technical publication, Compressed Air), which describe the demonstration project. This local effort accomplished three important milestones:

• It demonstrated the sponsor’s interest and ability to sponsor the restoration effort.
• It demonstrated the sponsor’s ability to raise money.
• It provided a model for the public and interest groups to see, and for technical entities to analyze possible with-project performance.

7.3 Study Management and Outreach

The study team was a multi-disciplinary group that consisted of several functional elements of the Corps and the local sponsors, and included study managers, the project manager (a wetland scientist), planners, civil design engineers, hydrologists and hydraulic engineers, environmental specialists, biologists, cost estimators, real estate specialist, economists, legal advisors, and geotechnical specialists.

The Corps and sponsor(s) conducted approximately four Steering Committee meetings and several property owner meetings each year of the study. The locally driven Steering Committee coordinated the management of the reconnaissance-level study with various Federal, state and local agencies, and environmental groups. The Steering Committee was comprised of representatives of the public, Federal, and State agencies, and special interest groups. The Committee obtained public views and comments on proposals, plans of study, scoping, impacts of proposed alternatives, and draft documents. At regular meetings during the reconnaissance study, the Steering Committee informed interested parties of the project’s progress to avoid misunderstandings. Local news reporters and congressional staff attended many of the meetings.

At the Reconnaissance Review Conference held March 31, 1994, eight representatives from private industry, private property owners, environmental agencies and organizations, and Teton County traveled to Portland, Oregon, to express interest in the approval of a feasibility-level study.

The local representatives, Teton County Commissioners Steve Thomas and Grant Larson, have stated clear support for the feasibility and implementation phase.

Much of the coordination efforts have focused on scoping the study to a cost level affordable to the county. Don Barney, Teton County Road and Levee Supervisor, and Rik Gay, Teton County Conservation District, have provided guidance and leadership at the local level. Mr. Michael Gierau, and most recently Bob Sherwin, Teton County Commissioners, have provided continuity from the previous (November 1994) Commission to the present Commission. The Walla Walla District met with the Commissioners on August 14, 1995, to further define the county’s concerns and financial ability, and have executed the Feasibility Study accordingly.

The study has received considerable media attention, which was facilitated and coordinated by the sponsor’s public relations person and Corps’ Public Affairs Officer. Four notable feature articles related to the study have been published: "The Snake," in the June 1996 issue of Wyoming Wildlife, official publication of the Wyoming Fish and Game Commission; an article in May 1998, in New York Times Science; an article in Spirit Magazine, Southwest Airlines of May 1999; and a feature from the January-February issue of Ingersoll-Rand’s technical publication, Compressed Air (see copy in supplemental section of this report).

7.4 Alternative Formulation Briefing Review Conference

An Alternative Formulation Briefing (AFB) Review Conference was held in Portland, Oregon on July 22 and 23, 1999. The AFB served to present the methodological approaches applied in the study’s various technical analyses and to ensure that the study was proceeding in compliance with Corps of Engineers planning and policy regulations. Conference attendees from the Corps of Engineers included representatives from HQUSACE, Northwestern Division, and Walla Walla District offices. Other participants in the conference included representatives of Teton County, Wyoming (study sponsor), Teton Conservation District (study sponsor), the National Fish and Wildlife Foundation, and local citizens.

The AFB was held to discuss and resolve issues identified in the review of a 75 percent draft version of the Jackson Hole Environmental Restoration Study Feasibility Report and technical appendixes to facilitate and accelerate the completion of the final Feasibility Report. Major issues identified included:

• Need for certified independent technical review documentation.
• Need for additional documentation of environmental habitat studies and trends.
• Need for discussion of relationship of proposed restoration features to surrounding ecosystem.
• Need for resolution of ability to use existing flood control levee easements for restoration project.
• Need for development of a comprehensive Real Estate Report (REP).
• Need for documentation of proposed schedule for construction phasing.
• Need for a complete list of local cooperation items in the report.
• Need to address potential efficiencies related to Federal and non-Federal maintenance responsibilities for the flood control and restoration projects.
• Need to address standards for utilization of tools developed in conjunction with the restoration project in locations along the Snake River outside the four specific study areas.
• Need to address permitting requirements in association with the Omaha Regulatory office with the goal of developing conditions for a Section 404 permit(s) for the use of restoration tools employed by this project to be used in development of regional permits for use by other interests.
• Need to address phased construction, monitoring, and adaptive management more generally.

Following the AFB, each of the above review items was addressed in preparation of a final draft Feasibility Report, which was submitted to HQUSACE for policy compliance review, along with documentation of the Independent Technical Review and a compliance memorandum indicating how and where each of the comments were addressed in the report.

7.5 Study and Review Teams

This section summarizes the technical review accomplished during the course of the Feasibility Study. This review process has involved the local sponsor(s), Corps technical staff, peer review from resource agencies and other interested parties, and formal independent technical review by the study’s Independent Technical Review Team comprised of members from the Corps of Engineers and the private sector. Participating agencies in development and review of the study are listed below in table 7.1. Table 7.2 lists the individual participants on the study and review teams.

7.6 Review Milestones

During the course of the Feasibility Study, there has been on-going, independent technical review of the major report products as they have become available. Major review milestones with reviewing entity and date of review are provided in table 7.3.

7.7 Independent Technical Review

Walla Walla District has completed technical review of the Draft Feasibility Report for the Jackson Hole Environmental Restoration Study dated December 1999. Notice is hereby given that an independent technical review has been conducted that is appropriate to the level of risk and complexity inherent in the project, as defined in the study’s quality control plan. During the independent technical review, compliance with established planning principals and procedures, utilizing justified and valid assumptions, was verified. This included review of assumptions, methods, procedures, and material used in analyses, alternatives evaluated, the appropriateness of data used, the level of data obtained, and reasonableness of the results. The independent technical review was accomplished by an independent team including members from Walla Walla District and contractors from Tetra Tech Inc. and Normandeau Associates.

The primary focus areas for independent technical review of the Feasibility Study were environmental studies, economic studies, hydrologic and hydraulic studies, cost engineering, and real estate. A team of qualified and experienced independent reviewers provided technical review comments for each of these categories. The review comments and all actions taken were recorded were and included in a Certification of Independent Technical Review memorandum on file with the project manger.

The nature of most comments was to ask for additional documentation or explanation of study methods and findings. Many comments were editorial in nature. None of the comments identified significant shortcomings or errors in study methods or findings. All concerns resulting from independent technical review of the draft Feasibility Report have been considered and addressed in the final report (and summarized in the attached Technical Review Comments forms) and then back-checked by the reviewer. In addition to the primary focus areas identified above, all associated documents required by the National Environmental Policy Act have also been fully reviewed.

7.8 Policy Compliance and Legal Review

Policy compliance and technical review issues identified at the Alternative Formulation Briefing were summarized in an Issue Resolution Memorandum following the conference. All issues were addressed in completion of the final Feasibility Report and were summarized in an Issue Resolution Compliance Memorandum submitted to Corps Northwestern Division and HQUSACE offices for review with the final report. The HQUSACE Policy Review branch will review the final report for consistency with all Corps of Engineers policy requirements. The final report has also been submitted to Walla Walla District Counsel for review and certification of the study’s legal sufficiency.

8. FINDINGS, CONCLUSIONS, AND RECOMMENDATIONS

8.1 Findings

Based upon the findings of this Feasibility Study for environmental restoration in Jackson Hole, Wyoming, the Progressive NER Plan is determined to provide the greatest public benefit. The Progressive Plan that is the result of subsequent management and sponsor review of this study, as well as coordinated partnering with regional agencies, interest groups, and the study team is recommended.

8.1.1 Progressive NER Plan

The Progressive Plan is estimated to create a total of 409,450 aquatic habitat units (an increase of 28 percent) over a 50-year period compared to without-project condition. The Progressive Plan will also create an estimated total of 24,425 riparian habitat units (an increase of 137 percent) over a 50-year period compared to without-project condition. The proposed Progressive Plan will not only improve habitat for the threatened and endangered species (i.e., the bald eagle, peregrine falcon, whooping crane, grizzly bear, and gray wolf) but will provide habitat restoration over the entire 22-mile study reach of the Snake River. The Progressive Plan provides the opportunity for greater ecosystem influence due to the restoration of highly degraded habitat over a larger geographic area. The expanded restoration effort will provide greater synergistic effect on adjacent habitats landward of the levees.

The Progressive Plan will use a phased construction approach, implementing restoration in Areas 1, 4, 9, and 10 before Areas A through H. The Progressive Plan will enable potential local sponsors to restore sections of the river more quickly and efficiently without the cost and time required for additional feasibility studies. Advancements in ecosystem restoration will occur as a result of Preconstruction, Engineering, and Design and from lessons learned during phased construction, monitoring, and adaptive management of those areas.

The cost per mile of restoration under the Progressive Plan varies along different parts of the river, but is within the range of costs determined for Areas 1, 4, 9, and 10. The total cost of the Progressive Plan is estimated at $52.3 million (1999 dollars). As noted in the FONSI, a factor in the elimination of the alternatives which included the additional areas suggested in the Progressive Plan was that the cost exceeded the local sponsor’s current ability to cost share. The areas in the Progressive Plan will be completed based on availability of anticipated funding of the local sponsor and the Corps.

The Progressive Plan is consistent with Congressional authority to study, evaluate, and make recommendations. The Progressive Plan provides the greatest opportunity for environmental restoration of all impacted areas of the Snake River below Grand Teton National Park and above the canyon section of the river managed by the USFS.

8.2 Conclusions

• The Snake River Flood Control Project created significant riparian and aquatic habitat declines due to flood control levee construction since the 1950’s. The Progressive NER Plan will restore and protect important fish and wildlife habitats impacted by the Flood Control Project.

• The Progressive NER Plan will provide restored habitats for multiple threatened and endangered species.

• The Progressive NER Plan will enhance diversity of animal and plant species in a geographical area in which fishing and nature-related recreation play a large part in regional and national economies.

• The Progressive NER Plan will result in optimal restoration over a more extensive portion of this outstanding natural environment.

• The Progressive NER Plan is identified as the preferred alternative over the Initially Proposed NER Plan based on the cost effectiveness analysis. The analysis shows that the Progressive NER Plan restores additional habitat at a lower cost per unit.

• A range of alternatives was considered. Besides the without project alternative, five alternatives were considered at the four initial study sites. The preferred alternative was identified at each site and was incorporated into the Initially Proposed NER Plan. The data was then extrapolated to the entire 22-mile river section which developed into the Progressive NER Plan.

• The Feasibility Report and EA present the findings of studies conducted for proposed environmental restoration to the authorized Snake River river channel near Jackson, Wyoming.

• The implementation timeline recognizes the sponsor’s ability to pay and outlines a phased project.

• Continuing construction, after the initial construction year, and monitoring combined with adaptive management will fine tune the restoration features to achieve greater cost efficiency.

8.3 Recommendations

I have given careful consideration to all significant aspects of this study, including engineering and economic feasibility, as well as public interest and environmental effects. The selected Progressive NER Plan described in this Feasibility Report and Environmental Assessment provides the optimum solution for restoring the authorized Snake River reach near Jackson, Wyoming.

I recommend that the 22-mile section of the Snake River be modified using the restoration techniques as described in this report. The total project cost is $66.5 million fully-funded ($52.3 million calculated under October 1999 pricing).

The project construction is phased in order to accommodate the sponsor’s request and ability to cost share in the project. While this strategy lengthens the construction period, the continuing construction combined with monitoring and adaptive management will actually achieve greater cost efficiencies and better long term results. Environmental habitat units will be gained in the very first construction year, and will continue to increase with each subsequent construction effort.

This conclusion reflects the information available at this time and current Corps policies governing formulation of individual projects. The conclusion does not reflect program and budget priorities inherent in the formulation of a national Civil Works construction program or the perspective of higher review levels within the Executive Branch. Consequently, the conclusion may be modified before implementation.

/signed/                              Richard P. Wagenaar Lieutenant Colonel, Corps of Engineers District Engineer

9. SUPPLEMENT

9.1 Final Report: Snake River Restoration Demonstration Project

9.2 Compressed Air, "The Good Flood"

---

---

---

stanley.g.heller@usace.army.mil