| OCR Text |
Show dDwnstream from the origin and 8 stream miles above the town of Duchesne. However, the Bonneville Unit would reduce existing flows in the portion of river between Hadcjs Creek tributary and Knight Diversion Dam by taking water from tributaries ( Hades Greek, West Fork of the Duchesne River, and Rock Creek) and thus lessening stream gains. Figures C- 4 through C- 6 depict representative seasonal flow patterns without and with the Unit. The hydrological effects of the Bonneville Unit would not be significant below the town of Duchesne and are not considered in this statement. Increased flows would occur during the summer months in Duchesne River below Starvation Reservoir due to return flow from Unit supplemental deliveries to irrigated lands along the lower reach of the river. Under Unit conditions, Duchesne River winter flows from Hades Creek downstream about 30 miles to Rock Creek would be virtually the sama as at present, because loss of tributary inflow would be so small. However, the flow reduction in Rock Creek would be sufficient to reduce the flow in the Duchesne River by about 30 percent down to Knight Diversion Dam. This reduction in flow should not exert a significant adverse impact on the fishery because the remaining water would be more than twice the minimum flow ( 45 second- feet) originally recommended by State biologists. At the dam nearly all the water is diverted into Starvation Reservoir thus reducing normal flow from about 150 c. f. s. to less than 25 c. f. s. Stream gains below Knight Diversion Dam are substantial and reach a favorable level shortly below Duchesne. It is expected that only the dewatering of the streaxii immediately below Knight Diversion Dam would have significant adverse impact on aquatic life. Approximately 7 miles of this section of stream is rated as Class III by the State and hence is of significant fishery value. The remaining 1 mile of stream is rated Class IV. During the spring or early irrigation season, Unit flows above Rock Creek would not be altered substantially from existing conditions. The sizeable diversion at Knight Diversion Dam below Rock Creek would not seriously affect the fishery during this period of peak flow since there would be about 600 c. f. s. of flow remaining. |
