| OCR Text |
Show irrigation downstream. Average summer flows would be reduced about 70 percent. Table C- 10 shows the historical flows without the Unit at the Vat Diversion Damsite, ( assumed to be the same as the flows 2.6 miles downstream at U. S. G. S. Gaging Station No. 9- 2750) and the estimated flows immediately below the diversion dam with Unit conditions. There would be virtually no water passing Vat Diversion Dam for 10 months of the year. Bureau of Reclamation streamflow studies1- 3 indicate that 5 to 12 c. f. s. of tributary inflows are produced by the 14 square miles of watershed surrounding the 5 miles of stream between Gaging Station No. 9- 2750 and Gaging Station No. 9- 2755. These accretions exclude the peak runoff months of May and June when spills through the dam would occur. Table C- ll shows the flows expected to develop just above the confluence with Wolf Creek and about 3.3 miles above the junction with the North Fork of the Duchesne River. Wolf Creek would be expected to contribute about 2 c. f. s. of additional flow. Minimum flows with the Unit would be about 30 percent of what they have been historically. Operation of Vat Diversion would severely reduce flows and probably eliminate fish habitat in the 2.6- mile reach West Fork immediately below the dam. However, the 5- to 12- c. f. s, tributary inflow below this point and the 2- c. f. s. contribution from Wolf Creek would be expected to preserve a limited fishery in the remaining 7.4 miles of the 10- mile total affected by the diversion system. The West Fork of the Duchesne River is an important Class III fishery for trout. Stream habitat studies have indicated that at least an 8- c. f. s. minimum flow must be sustained if the existing fishery was to be substantially preserved. No fishery releases have been included in the existing plan of operation for the Bonneville Unit. However, Bureau of Reclamation computations indicate that the critical flow of 8 c. f. s. would often be attained through accretion flows beginning at a point about 6 miles below Vat Diversion Dam. 312 |
