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601272 . . Draft Task 7 Technical Memorandum Peak stream flows, either daily or of longer durations, may play an important role in the recovery program for the endangered fish of the Yampa River. Because the model developed in this study operates on a monthly time step, it was not possible to evaluate the frequency or magnitude of peak flows for less than one month periods. Peak flow regimes may need to be more closely examined in future studies to evaluate the impacts to spawning and migration activities of the threatened and endangered fish. The tailwater and mainstem river fisheries were evaluated using the predicted stream flows at selected locations. The flows in tail water areas below Stagecoach Reservoir, Steamboat Lake and Elkhead Reservoir were compared for all scenarios. Each alternative scenario was compared to Scenario I (baseline). Both average monthly flows and minimum monthly flows were used in the evaluation. Habitat can be limited during the spring and summer months when flows are above normal, and during the fall and winter months when normal base flows occur. The late summer and fall period is an important period for squawfish moving back upstream from spawning areas. Low flows during this period may limit movement and decrease available habitat. For tailwater fisheries dependent on cold water, summer releases are important to maintain habitat conditions. However, excessive summer flows can limit habitat for young of the year trout and reduce recruitment into older year classes. The average streamflows downstream of Stagecoach Reservoir were similar in Scenarios I, II, III and IV. Streamflows substantially increased during summer months in Scenarios V when compared to Scenario I (Table 8). This increased summer flow could have negative impacts on the survival of young of the year trout below the reservoir although adult fish would probably be less affected. Under Scenarios II, III, IV and V, minimum flows downstream of Stagecoach were very similar to Scenario I. Under Scenario IV, during the months of July and August, minimum flows were substantially higher than minimum flows under Scenario I (Table 9). Minimum flows higher than those seen under the baseline scenario would generally be a benefit to the aquatic life. Average monthly flows below Elkhead Reservoir increased for Scenarios III, IV and V, as a result of the reservoir enlargement over the baseline conditions. Average monthly flows were less under Scenario II except during June through September. An increase in summer time streamflow could enhance a coldwater fishery downstream of the Elkhead Reservoir if suitable water temperature and water quality can be maintained. Habitat in this section of Elkhead Creek is currently limited by high sediment during runoff and high water temperatures. These water quality conditions would need to be improved to realize a more productive tail water fishery, The least effect on fluctuations in reservoir elevations and areas is seen under future demand levels in the no-action scenario (Table 10, Figure 16). Steamboat Lake elevation and area remains the same for all scenarios. There would be no effect on the fishery in Steamboat Lake as a result of the alternative scenarios. Elkhead Reservoir has the greatest amount of fluctuation in both elevation and area of all the reservoirs with the greatest fluctuation occurring in Scenario II. In Scenario II, reservoir surfaee area fluctuates by as much as 50 percent, while fluctuations in surface area under Scenarios III, IV and V were on the order of 40%. This amount of change in area could cause impacts to water quality with increased turbidity due to the annual flooding and exposure of de-watered areas. Areas exposed as a result of drawdown would likely be unvegetated and produce high amounts of turbidity due to wind and wave action. Increased turbidity could effect the downstream tail water as well as the reservoir fishery. 17 ,il.,__,,-