WSP09372 - Laserfiche WebLink

Home Browse Search

l)OlZ7~ . . Draft Task 7 Technical Memorandum Fluctuations in surface area and water surface elevation at Stagecoach Reservoir increase slightly under Scenarios II and IV compared to the no action case. This increased fluctuation could affect reservoir productivity. The reservoir fluctuations were similar under Scenarios I, III and V and little difference in the reservoir fishery and productivity would be expected. The no action alternative would have the least impact on the existing reservoir fisheries but also the least benefit to habitat in the instream flow reach at Juniper Canyon. All of the other four subsequent alternatives have some degree of impact on reservoir fisheries due to increased fluctuations in elevation and area. Scenario III has the least impact to fisheries of the four alternative scenarios. Scenario III also has the most benefit to reaches of the Yampa River designated as occupied habitat. Scenario IV and V would also benefit occupied habitat but slightly less than Scenario III. There would likely be little change in tailwater fisheries under any of the alternatives, although the flow regime downstream of Stagecoach and Elkhead Reservoirs will be altered. The flow increases downstream of Elkhead will benefit the aquatic life in that river segment if the water temperature and water quality are improved. The tail water fishery below Stagecoach Reservoir and Steamboat Lake should be similar under all scenarios. Flow Conditions in Occupied Habitat Flows in the Yampa River were evaluated at several locations both upstream and within occupied habitat. The main area of concern was the reach within Juniper Canyon and the potential effects on squawfish habitat. Results from all scenarios indicated an increase in late summer and fall flows in Juniper Canyon over the flows predicted in Scenario I (baseline). This flow regime should increase habitat in the Juniper Canyon reach over the no action scenario. Scenario III has the highest late summer and fall flows and could provide the greatest benefit to the habitat in this section of river. Flows in Juniper Canyon predicted in Scenario IV are slightly less than Scenario III. This is due to the relatively minor use of the reservoir to serve demands and the ability to store additional water at the upper end of the basin. Other sections of the Yampa River have less change than the Juniper Canyon reaeh except for reaches immediately downstream of Elkhead Creek. The reach upstream of the Williams Fork River has higher flows during most months of the year under all scenarios when the instream flow right is included in the model. Mainstem reaches upstream of Elkhead Creek, including the Morgan Bottoms reach, have some increase in flow but not to the extent seen in the lower reaches. Wetlands The three projects evaluated in Task 7 have impacts to existing wetlands due to both construction of the reservoirs themselves and due to reservoir operating strategies. However, as with the evaluation of streamflows and the potential to develop fisheries, it is not possible to select the best project of the three based solely on impacts to wetlands. Elkhead Enlargement The enlargement of Elkhead Reservoir has considerable merit in terms of minimizing impacts to wildlife and to wetlands. Because a reservoir is already in place, wetland and habitat destruction would be small compared to development of a new storage project elsewhere. Considerable wetland area around the periphery of the existing reservoir would be lost due to inundation. However, wetlands similar in characteristics and areal extent would likely be created along the periphery of the enlarged reservoir. 18 ;~