OCR Text |
Show An additional 3,000 acre- feet of water from Upper Stillwater would be conveyed through the aqueduct and used to maintain a minimum flow in Strawberry River below Soldier Creek Dam. Any unused part of the previously mentioned 3,500 acre- feet would be used to supplement the fishery releases below Soldier Creek Dam. The total annual diverted flow of Rock Creak under the proposed plan is estimated to be 82,900 acre- feet annually, which includes the 9,000 acre- feet divertible flow of South Fork of Rock Creek and the 3,000 acre- feet allocated for fishery releases below Soldier Creek Dam. Construction and operation of Upper Stillwater Dam and Reservoir would have the effect of reducing the flow of Rock Creek immediately below the dam to about 25 percent ( 10- 40 percent range) of the average flow during the winter months and causing a substantial reduction of the peak spring runoff flows. Average summer flows would be reduced by about 75 percent. Bureau of Reclamation reservoir operation calculations^ show that spills from the res. ervoir would occur during June and July about 24 out of 41 years. Releases to meet commitments for fish and irrigation are necessary 92 percent of the time during the period of study. For the remaining 8 percent of the time, only seepage past the dam would contribute to streamflow immediately below the dam and would usually occur during the summer and fall months when the reservoir would be full. Table C- 5 shows the historical flows of Rock Creek up Upper Stillwater Damsite and the estimated Unit flows immediately downstream from the dam. With Unit conditions a flow below the dam of 5 to 11 c. f. s. ( an average of 8 c. f. s.) would be maintained during winter months to meet fishery commitments at the U. S. Forest- Indian boundary and a flow of 29 to 170 c. f. s. excluding reservoir spills, during the summer months would be maintained for irrigation. The watershed between the damsite and the confluence with South Fork Rock Creek contributes about 18 to 24 c. f. s. to the flows of Rock Creek |