OCR Text |
Show during the summer months but only 2 c. f. s. during the winter months. Table C- 6 shows these estimated tributary inflows and stream gains. Table C- 7 shows the estimated tributary inflows and stream gains to Rock. Creek between Upper Stillwater Dam Site and Ashley National Forest-- Uinta and Ouray Indian Reservation Boundary. These flows, averaging 18 to 67 c. f. s., combined with the releases from Upper Stillwater Dam make up the estimated flow of Rock Creek at the Forest and Indian Boundary. The fall and winter stream gains average about 20 c. f. s. Table C- 8 shows the historical flows and estimated Unit flows for Rock Creek at the Forest- Indian Boundary. Rock Creek winter streamflows, with the Unit, would be reduced to about 50 percent of the historical flows. Flows would be less than 25 c. f. s. only during a year similar to 1934 when the minimum flow was estimated to be 5 c. f. s. Average summer flows would be about 35 percent of the historical pattern. Analysis of post- Unit streamflow conditions indicate that the severely reduced flows in Rock Creek below Upper Stillwater Dam would virtually eliminate fish habitat in the 1 mile downstream to the confluence with the South Fork of Rock Creek where stream gains are minimal. In the 7- mile reach from the South Fork of Rock Creek to the Forest- Indian Reservation Boundary further stream gains would accumulate from the surrounding watershed and the recommended flow of 25 c. f. s. for the Indian lands would be maintained and exceeded. The South Flank geological fault mentioned in Section B appears to have a variable effect upon the downstream flow. Table C- 9 shows that periodic stream gains and losses have occurred between Upper Stillwater Dam and a point about 5 miles downstream. In seven sets of measurements obtained between 1947 and 1964 there were four that showed gains and three that showed losses. There is insufficient data available to predict what effect the fault zone would have under Unit operational conditions. It is planned to carry out additional studies in this area to assist in making decisions concerning the operation of the proposed feature. The recommended minimum flow of 25 c. f. s. at the Forest- Indian boundary would be maintained. |