9320 - Laserfiche WebLink

Home Browse Search

26 of those surveyed, the relationship of surface area, depth, volume and velocity to reduced discharge is indicated diagrammatically in Figure 12. _ It is evident from the conclusions above that considerable reduction in discharge can occur without greatly changing the surface ~ . area or appearance of the stream. However, the basic but less obvious fish habitat factors of depth and velocity are more directly proportion- al to discharge, and they may be so reduced as to critically affect trout stream production without appreciable change in surface area or appearance. -The stream surface area was mapped by habitat types and plan- imetered for each station from one to four times as the discharge changed normally or by controlled diversion. The tables of habitat type areas are included in the Appendix D. With reduction of discharge there is a general tendency (a) for pool area to be reduced because of lesser ~~ depths; (b) for deep fast to become riffle as depth and velocity are . lowered; (c) for riffle to become slow shallow; and (d) for slow shallow to become dry rock (Figure 13). The net effect of these changes depends upon the characteristics of individual streambed sections and the extent of discharge reduction. The reduction of fish habitat on the Sweetwater was best illus- trated at Station I with discharges of 42, 22, 16 and 7 c.f.s. (Figure 14 and 15). The amount of fish habitat on the South Fork, Station VIII, at flows of 59, 22, 14, and 8 c.f.s. is presented (Figure 16 and 17). Detailed tables (Appendix D) and charts (Appendix E) were _ prepared to show the effect of discharge reductions on fish habitat types. Erosion.--The watershed of both Sweetwater Creek and South Fork consist generally of a volcanic cap at the upper elevations, and