Response:
Split-season alternatives are closer in shape and biological performance to the natural hydrograph than the Corps of Engineer’s Current Water Control Plan or other alternatives that are currently under consideration for the Master Manual. Elements of the historical hydrograph captured by the split-season alternatives include higher flows up through mid-June (historical peak flows generally occurred near the end of June) and lower flows from mid-July through mid-August (flows generally declined steadily beginning in early July and continuing through the summer, fall, and early winter). The spawning period of Missouri River native fishes and nest initiation by interior least terns and piping plovers occurs during the upward or downward slope of the historical hydrograph.

Replicating the duration, magnitude and timing of the river’s historical flow regime is not possible nor desirable to basin residents. The Corps of Engineers (Corps) has indicated that implementing a "natural hydrograph," as represented by their run-of-river flow simulation termed EVQ2, would eliminate the other authorized purposes of the reservoir system including flood control, navigation, hydropower, irrigation, and other uses. Proposals, such as the one advocated by the Missouri River Natural Resources Committee which incorporate higher spring flows and lower summer flows from Gavins Point Dam, were formulated based on this fact as well as sideboards for flow timing and magnitude established in the Corps Preliminary Revised Draft Environmental Impact Statement (PRDEIS). Biologists are focused on reproducing the shape of the historical hydrograph (an ascending and descending limb) during the important spawning and nursery periods of fish and during nesting by terns and plovers, while taking into account the need to maintain other project purposes.

Development and selection of reservoir operation alternatives also must be based on biological performance through time given varying water supply conditions throughout the system. Through modeling, the Corps’ uses environmental value functions to predict how different reservoir operations affect habitat for Missouri River fish and wildlife, including endangered species. For native fish, including the pallid sturgeon, the most important value functions to analyze are the native fish habitat index and wetlands; for terns and plovers the value function of interest is the tern and plover habitat model.

Because split-season alternatives are closer to the "natural hydrograph" than current operations they provides greater benefits to native fish and terns and plovers as measured by the value functions. Average habitat values summed over all river reaches for the native fish index, wetlands, and tern and plover habitat are all higher with a split-season alternative than the current plan. Habitat values in priority recovery areas for pallid sturgeon and terns and plovers are also higher with the split-season alternative versus the Current Water Control Plan. For example, the MRNRC alternative produces almost 65 % greater habitat for terns and plovers than current operations in the priority recovery reaches below Garrison, Fort Randall, and Gavins Point Dams. Except for the unchannelized reach downstream of Gavins Point Dam, native fish habitat values for the pallid sturgeon and other native fish are all higher for the MRNRC alternative than current operations in the priority recovery areas for pallid sturgeon below Fort Randall Dam downstream to the mouth at St. Louis, Missouri.

Concern: Historic Flows Do Not Provide Historic Habitat Conditions; The Channel Has Changed.

Historic flows, as simulated by EVQ2, the Corps run-of-river simulation, produces the highest native fish habitat values of any alternative even in reaches which have changed morphologically. This is true for both remaining unchannelized reaches of the river downstream of Fort Randall Dam and Gavins Point Dam, and in the channelized river below Sioux City. Therefore, even with today’s channel, historic flows produce the highest amount of native fish habitat.

Whether higher reservoir levels adversely impact the pallid sturgeon, least tern, and piping plover depends on when the higher levels occur and the amount, suitability, and duration of riverine habitat and reservoir shoreline habitat that would be exposed by lower reservoir levels.

The various split-season proposals, in comparison to the current Master Manual, will maintain higher reservoir levels during serious, long-term droughts (such as the 30s, 50s, and 80s). In other years, the reservoirs will be unbalanced; that is, one of the big three reservoirs–Fort Peck Lake, Lake Sakakawea, or Lake Oahe will be drawn down several feet on average once every three years. This type of intrasystem regulation will not only benefit reservoir sport fisheries but also enhance nesting habitat for the birds by alternately exposing and inundating shoreline habitats. During the first year of an intrasystem drawdown, exposed shoreline habitat would be available to nesting birds. This habitat would probably become unsuitable in the second year because of encroaching vegetation; however, in year three inundation of the habitat would remove the vegetation and allow a drawdown to again expose suitable habitat in subsequent years.

Riverine and shoreline habitats exposed during serious, long-term droughts may initially provide suitable nesting habitat for terns and plovers, but their habitat value will rapidly decline as vegetation encroaches after the first year. For pallid sturgeon, even long-term droughts will not provide any short-term habitat benefits. Reservoir headwater areas have extensive mudflats and areas of very fine (silt) substrates unsuitable as pallid sturgeon spawning habitat. It would take many years of low reservoir elevations coupled with proper river flows to flush out the silt and sort substrate into the larger sand fractions used by pallid sturgeon. Proper water temperatures and flow regimes in the headwater areas would also be needed to provide any benefit to pallid sturgeon from increasing riverine habitat in reservoir headwater areas. Lower reservoir elevations during the late 80s/90s drought did not produce young pallid sturgeon in the river reaches between Lake Oahe and Garrison Dam or Lake Sakakawea and Fort Peck Dam because the proper flow regime and water temperatures were absent. Most importantly, it should be remembered that long-term droughts in the Missouri Basin occur only 2-3 times a century. Even if these droughts resulted in increased habitat in reservoir headwaters and along reservoir shorelines, endangered species do not have the luxury of waiting 20-30 years between serious drought events to take advantage of suitable habitat conditions.

Better flow management in existing riverine habitat areas, especially the reaches below Garrison, Fort Randall, and Gavins Point Dams, rather than reservoir shoreline habitat, is the top priority for management emphasis. Optimizing flows in these habitats rather than maintaining lower reservoir pool levels during a drought is far more important to recovery of these species. Production and fledge ratios for both species are higher in riverine habitats.

The lower summer flows from Gavins Point Dam proposed in the split-season alternatives are more than adequate to meet water supply and water quality requirements in the lower river. Native fish, including pallid sturgeon, coped with even lower flows, in a much wider channel, prior to development of the river. There is some question as to whether the lower flows may affect permit requirements for once-through cooled power plants on the river in Nebraska which discharge heated water to the river. Regardless of the permit requirements, previous studies of thermal discharges in the Nebraska/Iowa reach of the river by University of Nebraska, Nebraska Game and Parks Commission, and utility researchers concluded that power plant discharges effected only a small area of the river and had little effect on the river’s aquatic community, including fish.

The split-season alternatives propose lowering flows from mid-June to mid-August to enhance production of terns and plovers during the nesting period. In combination with the higher spring flows proposed, this will create a stage drop within the nesting habitat of the birds of about 2.95 feet.

This drop provides the optimum amount of freeboard on the nesting sandbars to protect nesting terns and plovers from uncontrolled summer runoff events according to tern and plover biologists. Higher flows during the nest initiation period force birds to nest on the highest sandbars. Subsequent low flows provide increased protection to eggs, hatchlings, and unfledged birds through mid-August when the birds fledge.

During the winter of 1999/2000, Gavins Point releases were reduced to 17 kcfs. Inspection of river habitat conditions at this flow by biologists indicated that habitat conditions were good below Gavins Point at this flow with numerous side channels (for feeding habitat) and isolated sandbars observed. Provision of scouring flows to periodically restore high elevation sandbars, higher flows during nest initiation to force birds to nest at higher elevations on the sandbar and stable to declining flows during the nesting period are the key to tern and plover reproductive success and recovery.

The Current Water Control Plan is inadequate for tern and plover recovery. Lack of high flows during normal runoff and drought periods results in tremendous losses of sandbar nesting habitat and a consequent increase in loss of chicks to both flooding and predation.

The Pallid Sturgeon Recovery Plan, which was developed by recognized experts in pallid sturgeon biology, recommends restoring natural river flows as much as possible below Gavins Point Dam. This reach of the river, which includes the unchannelized reach from the dam downstream to Ponca State Park, and the channelized river below Sioux City, Iowa, is identified in the Plan as a recovery-priority area for pallid sturgeon. The Plan also identifies the reach below Fort Randall Dam (from 20 miles above the Niobrara River confluence to Lewis and Clark Lake) as a recovery-priority area. Neither of these two areas can be managed in isolation because altering the flow regime for either Gavins Point Dam or Fort Randall Dam will influence the other as there is little storage in Lewis and Clark Lake.

The split-season proposal recommended by the MRNRC increases physical habitat for pallid sturgeon in the Fort Randall Reach and in the river below Sioux City, Iowa. In addition, higher spring flows have other benefits not accounted for in the physical habitat value function. High spring discharges: 1) serve as cues for fish such as pallid sturgeon, paddlefish, blue suckers and other native species to move to spawning areas; 2) seasonally inundate connected wetlands, backwaters, and side channels which serve as spawning, nursery, and food production areas for fish and provide seasonal habitat for migrating birds ; 3) introduce woody debris and detritus into the channel. Woody debris and detritus are the foundations of the food chain in the open river reaches of the Missouri River.

The National Academy of Sciences recommends restoring the pre-development hydrograph as much as possible to restore ecosystem function in large rivers. Research work sponsored by the MRNRC also showed that river flows during the spawning period influenced the abundance of many native fishes in the Middle Missouri River which includes the reach below Gavins Point Dam. Abundance of fishes increased with increasing spring discharge. River biologists recommend restoring both flows and channel and adjacent floodplain habitats in the Missouri River below Gavins Point Dam. Restoration of flows is needed to make main channel, off-channel, and floodplain habitats function properly, i.e., side channels, backwaters, wetlands, and sandbar pools must be wet at the right time of year. This will not only benefit endangered species, but other species important to the river and people, including catfish, bass, crappie, sauger, walleye, and waterfowl.

The bed of the Missouri River has lowered substantially over time from Gavins Point Dam downstream to the Platte River confluence. This is because the water released from the dam is sediment-starved and erosion of the bed occurs as a result. This phenomena is termed bed degradation and leads to lowered water tables and dewatering of side channels, backwaters, and floodplain wetlands in the affected reach.

Degradation (lowering) of the riverbed in important recovery areas underscores the need to release more water at the right times to reconnect side channels, backwaters, and wetlands with the main channel. These connected habitats are critical to a host of river fish and wildlife, including many species of native fish. Reconnecting isolated habitats using flows is also less costly than the very expensive construction costs associated with channel and floodplain restoration in reaches having bed degradation and/or engineering constraints associated with maintenance of a commercial navigation channel. Higher spring, summer, and fall flows of the past several years below Gavins Point Dam provided important backwater connections that enhanced fishery production, fishing opportunities, and waterfowl habitat along the channelized river. These flows also were of sufficient elevation to scour sandbars of vegetation greatly increasing nesting habitat for terns and plovers and roosting habitat for migrating waterfowl and shorebirds.