APPENDIX C - RIVER WORK AND MAINTENANCE
Introduction and Past History
Prior to construction of flood control and storage dams on the Colorado River, the lower river from the present site of Hoover Dam to the Gulf was typical of a river carrying a heavy sediment load over an alluvial bed. Before the dams, the river was actively building up the alluvial valleys by repeated inundation when the spring snowmelt flowed from the upper river basin. Each annual flood caused the river to meander across the alluvial valleys, cutting and depositing material in the classical meander patterns. During the ebb of the flood the river typically deposited a remainder of its sediment load on the valley floor.
The dams impounded the heavy load of sediment the river historically carried down from the upper basin, and significantly reduced the flood flows which carried most of the sediment through the system. The clear water released from the dams entered the channel practically free of sediment and immediately began acquiring a new sediment load. The dams caused the residual coarse sediment in the river to be redistributed with the result that farther downstream, below each dam, the quantity of sediment was sufficient that the river continued the natural process of meanders and aggradation.
Although river maintenance work started near Yuma, Arizona, prior to 1925, Congress did not pass the CRFWLS Act until March 3, 1925. The present authority under which Reclamation operates the Colorado River Front Work and Levee System is the Act of June 28, 1946. This act authorized appropriations for controlling the floods, improving navigation, maintaining the banks of the Colorado River, dredging and straightening the river channel, and conducting studies necessary to fulfill the foregoing objectives.
The physical control and training of the lower Colorado River have generally been accomplished by the construction of the system of levees, river realignment, and river control structures. River control structures include bankline reinforcement, riprap, jetties, and training structures. The dredging activities have been used for channel realignment, development of material for levee construction, sediment control, and environmental enhancement.
Reclamation's Yuma Area Office (YAO) is responsible for maintenance of the Colorado River from the SIB to Davis Dam which is approximately 276 river miles. Each year YAO performs an inspection of the Colorado River and identifies bankline areas, levees , and river structures that require maintenance (Table C-1). For this ongoing maintenance activity on the river and levees, YAO has a need for up to 60,000 cubic yards of riprap and up to 20,000 cubic yards of gravel per year. Normally Reclamation crews perform the
Table C-1. Levee & bank line system for the lower Colorado River by river-miles and division.
| LEVEE | BANK LINE | |
|---|---|---|
| 1. LIMITROPHE DIV. RM.00 TO RM.22.1 | ||
22.10 | | |
| 4.0 | |
| 2. YUMA DIV. RM.22.1 TO RM.43.2 | ||
3.7 | | |
7.9 | | |
11.4 | | |
4.2 | | |
| 6.5 | |
| 3. LAGUNA DIVISION RM.43.2 TO RM.49.2 | ||
| 4.73 | |
| 4.73 | |
4. CIBOLA DIVISION RM.87.3 TO 106.5| | | |
14.4 | | |
| 16.25 | |
14.8 | | |
| 18 | |
5. PALO VERDE DIVISION RM.106.5 TO RM.133.8| | | |
| 22 | |
| 22 | |
2 | | |
6. PARKER DIVISION RM.133.8 TO 177.9| | | |
| 12.2 | |
| 12.95 | |
7. MOHAVE DIVISION RM.233.9 TO 276| | | |
25.4 | | |
| 20.6 | |
| 13.75 | |
7.9 | | |
| 9.75 | |
| TOTAL * | 113.8 Miles | 167.46 Miles |
* Totals include sum of miles for both banks of the Colorado River
maintenance by hauling and placing the riprap on the banklines and levees. Reclamation endeavors to locate the quarry sites within economical haul distances from the stockpile sites.
With the exception of bankline work in the Yuma and Limitrophe Divisions, most needed levees and banklines along the lower Colorado River are in place, and future work will not require the construction of new structures. Future work will only include periodic structure repair and stockpile replenishment as required to compensate for material that has been used for routine maintenance requirements and to repair flood damage. The annual amount of material needed may vary. The anticipated annual average need is 80,000 cubic yards of mined material through the year 2005.
Material used for routine maintenance activities and to repair flood damaged structures can be obtained from approximately 45 existing material stockpile sites. These sites are located along the lower river from near Davis Dam to the SIB. Material from any of these stockpiles may be used to repair flood damaged structures. The anticipated 80,000 cubic yards of material needed to annually replenish these stockpiles may be obtained from any of the existing quarries as shown on Figure C-1.
The first dredging on the Colorado River system occurred in the Yuma area in the early 1900s, and during the following 40 years incidental channel improvements were effected to correct local problem areas. Dredging is by definition the excavation of material under water, and the first machines were essentially of the dragline or bucket type.
The Bureau of Reclamation acquired the 16" hydraulic suction dredge "Colorado" in 1949. Work began in the Mohave Valley area to alleviate the flooding problem at Needles and was extended upstream to stabilize the meandering channel alignment. Subsequently, the dredge "Colorado" was moved to the Blythe area in the southern Palo Verde valley where it accomplished the channel realignment known as the Cibola Cut. The "Colorado" was then dismantled and replaced with 12" hydraulic suction dredges which are better sized for the scope and nature of the maintenance dredging and the remaining improvement projects.
The present and foreseeable dredging program is described later in the sections pertinent to specific river divisions.
The Colorado River system has approximately 50 backwaters that would benefit from dredging and other physical renovation. The Back Water Subcommittee of the Lower Colorado River Coordinating Committee is presently prioritizing a list. Reclamation is prepared to provide dredging to those backwaters on a cost-shared basis.
Major Activities Along the Lower Colorado River
For administrative purposes the lower Colorado River has been divided into maintenance divisions which are roughly determined by different physical characteristics, which are shown in Figure 2. The following discussions are indexed according to those divisions.
Mohave Valley Division
The Mohave Valley Division is located between Davis Dam and the Topock Gorge. It is the northernmost of the ten divisions organized under the Colorado River Management Program. It includes the Cities of Laughlin, Nevada, Bullhead City, Arizona, and Needles, California.
Hoover Dam significantly reduced the annual floods that purged the lower Colorado River, however, flows were still large enough for scour and developed sediment to remain significant. Subsequent deposition of the sediment in the headwater delta area of Lake Havasu above Parker Dam, created a problem of severe aggradation in the lower Mohave Valley. At Topock, deterioration of the channel induced more deposition, and by 1943, sandbars extended across the entire channel causing water levels upstream to rise and cause serious flooding at Needles. Although emergency protective works were undertaken, channelizing the river was the only permanent solution. Channel stabilization was initiated in 1949 with the dredging of an improved channel between Needles and Topock and the river was diverted into the new channel on June 25, 1951. To prevent the same aggradation process from repeating itself, the Topock Settling Basin was constructed in order to reduce the flow of sediment into Topock Gorge. This work and associated levee construction eliminated the immediate flood threat to Needles. However, it did not, by itself, provide the river stability between Davis Dam and Topock which was needed to assure that the problem would not recur.
Channel dredging, levee construction, and associated bankline stabilization work which reduced the pickup and transport of sediment, were subsequently accomplished upstream from Needles to a point 10 miles below Davis Dam. The continuous dredging in the Topock Settling Basin was suspended in 1982 due to the gradual reduction of the sediment loads being scoured from the river as the bottom material coarsened and the river approached a steady regime level. Reclamation continues to monitor the sediment transport and river conditions. Dredging has continued in the basin since 1982 on an intermittent basis, and there is a likelihood that maintenance dredging may be required within thenext ten years.
Related work for the improvement of fish and wildlife habitats and recreational features has also been provided. Topock Marsh, which owes its existence to the completion of Parker Dam and the subsequent filling of Lake Havasu in 1938, has been encompassed with a dike to maintain water levels at an elevation of 455 feet above mean sea level (msl). At this level, approximately 4,000 acres of open water are available for fisheries and wildlife management. Inlet and outlet structures were constructed by Reclamation to control water apportioned to the Havasu National Wildlife Refuge. The high flows of 1983 and 1984 flooded parts of the Mohave Valley above Topock Marsh. As a result, a new flood control structure, Topock South Levee, was constructed in order to prevent mainstem floodwater from backing into Topock Marsh. At the same time, revegetation, water control structures, and aquatic habitat development were designed to enhance fish and wildlife conditions. Reclamation also participated in the development of the Needles Marina and Park Moabi near Topock. Popularity of these marinas has increased each year since their construction. Beal Slough, a 30 acre backwater in the latter stages of succession, was dredged by Reclamation in 1979 and 1980 as a part of a cooperative study project aimed at fish and wildlife benefits.
Topock Gorge Division
The Topock Gorge Division extends from the upper end of Topock Gorge to the upper end of Lake Havasu. Minimal maintenance work has been conducted in this Division in the past, due to the natural channel configuration and substrate, which consists of a deep channel bounded by high canyon walls. These are broken to form various small backwater wetlands. This division is entirely within the Havasu National Wildlife Refuge.
Havasu Division
The Havasu Division includes all of Lake Havasu and the river between Parker and Headgate Rock Dams. The effects of the high flows on the river are marked in this division by sediment deposition in the upper end of Lake Havasu. The high flows of 1983 and 1984 deposited 10 million cubic yards of river sediment and extended the existing delta.
The water level in Lake Havasu fluctuates between 440 to 450 feet msl in accordance with the Parker Dam operating criteria, although for practical purposes, the lake elevation has been maintained above 445 feet msl for the last 15 years. During a flood, a potential surcharge to elevation 455 feet msl may develop.
In the Parker Dam to Headgate Rock Dam reach, an area commonly known as the Parker Strip, water levels are determined by discharge from Parker Dam and the backwater effect from Headgate Rock Dam. General channel stabilization activities are minimal due to the channel and bankline substrate. Most stabilization activities in this reach are conducted by entities other than Reclamation to protect local facilities.
This division is the most intensely developed area for recreation along the river. The Parker Strip has been heavily developed for recreation purposes, and in recent years thousands of people have visited Lake Havasu to boat and water ski. Flood releases of 40,000 cfs from Parker Dam in 1983 caused damage to homes and businesses with river frontage in the Parker Strip.
Parker Division
The Parker Division is located between Headgate Rock and Palo Verde diversion dams, and encompasses most of the lands of the Colorado River Indian Tribes’ Reservation. It is divided into two sections, Parker I & II, for better administration of the division. Parker I begins at Headgate Rock Dam and ends 2 miles south of Agnes-Wilson Bridge. Parker II starts at River Mile (R.M.) 163.3 and extends to R.M. 133.8, at Palo Verde Diversion Dam.
The channel improvement work in Parker I was completed by 1967. The major aspects of the Parker II channel improvement and stabilization work was completed in early 1995. During the next few years, as the river adjusts to the channel improvements, minor corrective work may be required.
No Name Lake is a backwater area located in the Parker II Division. Approximately 1,200,000 cubic yards of material are to be excavated and placed in the designated areas to restore the Lake to pre-1983 conditions. This is a portion of the mitigation for the Parker II Channel Modification Project.
Other potential marsh and aquatic enhancement in this division includes the rehabilitation of the Deer Island complex, a large lake and marsh in the Parker I area.
Palo Verde Division
The division begins at the Palo Verde Diversion Dam and extends to Taylor Ferry near the Imperial County, California line. Channel stabilization and other improvements are essentially complete in the Palo Verde Division and work primarily consists of routine maintenance and repair to structures. Previous work in this area consisted of earthfill training structures and bank protective riprap designed to prevent random meandering.
C-8 Backwater is located in the Palo Verde Division south of Blythe. It is a mitigation feature which Reclamation maintains. Rehabilitation work was begun in C-8 but was suspended early in 1995 due to lack of funding. It is currently planned to complete C-8 after the work in No Name Lake. Approximately 10 months of work still remains.
Cibola Division
The Cibola Division extends 19 miles from the lower end of the Palo Verde Division to Adobe Ruin, near Walter’s Camp. Through much of the Cibola Division, the natural channel was shallow due to sediment deposition. A program to correct channel deficiencies by dredging and constructing levees was initiated in 1964 and completed in 1970. The old river channel was essentially abandoned and became a part of the Palo Verde outfall drain. The river channel in this division is totally stabilized through the use of dredging, bankline riprap, training structures and jetties.
Three Finger Lake is a decadent wetland located on the old river channel and within the Cibola National Wildlife Refuge south of Blythe, California. Approximately 800,000 cubic yards of material have been excavated and placed adjacent to the design lake configuration to restore the lake to its historic conditions. This is a cost-shared effort with FWS.
Imperial Division
The waters behind Imperial Dam, including associated backwater areas constitute the Imperial Division. The division extends through the reach from the lower Cibola Valley, to Imperial Dam. This division receives the sediment generated in the Parker, Palo Verde, and Cibola Divisions. The sediment load arriving in the Imperial Division is either deposited in the overflow areas outside of the main channel or eventually arrives at Imperial Dam to be removed in the desilting works and the forebay of the dam.
In planning for the Parker, Palo Verde, and Cibola Divisions, reducing the sediment flowing into the Imperial Division was a major objective. Reclamation continually collects and processes data on sediment transported by the river. This allows needs to be defined, appropriate corrective measures to be instituted, and the results of control measures to be adequately evaluated.
Most of the diverted sediment is removed by the Desilting Works for the All-American Canal, returned to the river below Imperial Dam and dredged to permanent dry land storage areas near the Laguna Settling Basin, located about 1 mile above Laguna Dam. The desilting works for the Gila Gravity Canal are maintained periodically, by sluicing sediment accumulations down to the Laguna Settling Basin for removal by dredging.
Dredging above Imperial Dam is conducted periodically to maintain diversions for water demand into the All-American Canal on the west end of the dam and the Gila Gravity Main Canal on the east end.
In the main channel above the California sluice gates on the California side of Imperial Dam, about 900,000 cubic yards of material have accumulated over a period of years. This material will eventually be pumped into the river channel below the dam, probably in the next 3 to 5 years. This area is approximately 480 feet by 2,500 feet and is to be cleaned to a depth of about 20 feet. Normally it takes approximately 6 months to a year to clean this area.
The Gila Gravity conveyance channel, just upstream from the dam face, has required periodic work. About 300,000 cubic yards of sediment accumulated here over a period of years and eventually must be pumped by dredge into the river channel below the dam gate for transportation to the Laguna Basin; probably some time in the next 2 to 3 years. This channel is approximately 360 feet wide by 1500 feet long and is dug to an average depth of 15 feet for a total of 300,000 cubic yards of sediment. Working a two-shift schedule it would take 4 months to clean the channel.
Laguna Division
The Laguna Division includes the area between Imperial and Laguna Dams. The Laguna Division receives the sediment returned from the All-American Canal Desilting Works. Because this created problems associated with Mexican diversions at Morelos Dam, in the mid 1960s, Reclamation constructed a settling basin in the Laguna Division where sediment from upstream sources is trapped and pumped with a dredge for disposal onto dry land.
The basin is presently about 50 percent full, and 1 million cubic yards of material will be excavated and disposed of in the adjacent established disposal sites within the next 3-5 years. The work in the Laguna Basin is required periodically as a routine maintenance function.
The time span between dredging depends on the sediment load. Under the present forecasts it appears the work may be scheduled at 5 year intervals. The settling basin is approximately 4,000 feet long by 500 feet wide and is normally excavated to a depth of about 25 feet. The total capacity is approximately 2 millioncubic yards. Working a two-shift schedule it takes approximately 12 months to excavate the basin when it is half full. It is necessary to keep the basin at about half capacity or less, since the trap efficiency (ability to capture sediment) drops off dramatically as it passes the half-way point.
Included within this division is Mittry Lake, a shallow lake east of the Colorado River channel and north of Laguna Dam. The lake has a surface area of approximately 750 acres and is fed by an inlet structure originating at the head works of the Gila Gravity Main Canal.
Yuma Division
The Yuma Division is the reach of the river located between Laguna Dam and Morelos Dam. The river channel extending from Laguna Dam to the upper end of the diversion pool above Morelos Dam was formed by the undiminished natural flow of the river before the dams were constructed. This dominant flow, the flood flows most affecting the channel shape, averaged about 20,000 cfs with maximum flows in the early 1900s exceeding 200,000 cfs, depending upon the time of year and location within the division. While the historic riverbed averages 600 feet in width, only about 120 feet is presently occupied by river flows. The remaining portions of the riverbed, at or near the elevation of ground water, support various growths of vegetation: cattails, cane, arrowweed, saltcedar, mesquite, cottonwood, etc. Above Yuma, vegetation has been partially controlled by intermittent programs of vegetative control - mowing or cultivating.
A 1969 plan for this division called for renovation of the low-flow channel by dredging, reshaping, and lowering the water table under the remainder of the riverbed, and instituting a program of vegetative control. After completing most of the work in the upper 6 of the 20 miles of river channel in the division, the work was suspended pending resolution of environmental concerns. These concerns were met by dredging the area which is currently the open water in Mittry Lake. Prior to that, little open water existed. The lake is now heavily used for fishing.
During the high flows of 1983-1984 the channelization work was destroyed, and the river attacked the levees in several places, which resulted in emergency maintenance. The whole floodplain was essentially inundated, and farm drainage was severely affected.
The 1993 Gila River flood deposited 10 million cubic yards of sediment in the Colorado River channel from the confluence of the Gila River to Morelos Dam and raised the river bottom an average of about 5 feet. This has resulted in complaints from local farmers that the elevated river bottom resulted in groundwater problems in the area.
Due to the flooding of the Gila River in 1993 and high water releases from Painted Rock Dam in 1995, there exists a good probability that dredging will be required. The sediment load in the river channel increased by about 10 million plus cubic yards during the 1993 flood, and with the present Gila flows, that will increase even more. This sediment needs to eventually be removed to increase the capacity of the river channel to prevent overtopping the levees during large floods and to lower the water table in the Yuma valley. Should the funding and permits to do the work be made available, this work will probably be done in the next 10 years. Separate consultation under section 7 of the Endangered Species Act would be conducted for this project. The area to be dredged is located from the confluence of the Colorado River and the Gila River west to Morelos Dam. Should surplus flows on the Colorado River occur in the next 5 to 10 years, these flows may be used to sluice the sediment through the system in lieu of dredging.
Dredging of the river channel between Morelos Dam and the NIB, to relieve the sediment load to Mexico's irrigation system, was completed April 12, 1995. Unless a major flood event occurs or a general dredging project below the Gila confluence is undertaken, it will most likely be necessary to maintain this part of the channel periodically.
Reclamation has an ongoing planning project for the rehabilitation of the river from Laguna Dam to Yuma.
Limitrophe Division
The Limitrophe Division extends from Morelos Dam near Yuma, Arizona, to the SIB near San Luis, Arizona. The river channel in this Division is essentially dry during normal water years, due to the diversion of water for Mexico at Morelos Dam. The United States and Mexico are currently working on plans to relocate the river's channel and increase its flow capacity in this Division to handle conditions such as the flooding during 1983-1985. Severe property damage occurred to Mexico during that time.