WSP07787 - Laserfiche WebLink

Home Browse Search

RESOURCE USE For FISH HABITAT (Con.) Description of Area: Virgin Valley Sub evaluation Unit, Arizona, Nevada, Utah Future Conditions PlmmiDll Alternatives Future I I Without 1 2 Unit Present Conditions Parameters Low flows at the Riverside, Nevada gage were analyzed. Analysis of low flow is of greater significance to fish habitat than average flow previously discussed. Low flow was found to increase from no flow to 16 cfs for Alternative l,and 20 cfs for Alternative 2. This low or a lower flow could be expected to occur on the average of one year out of ten years. Considering variation in flow in any month and flows which would be expected to have occurred before irrigated agriculture activity on the Virgin River, the flow variation caused by the proposed salinity control pro- gram is not measurable. Salt load carried by surface flow increases for Alternative 1 and 2 due to increased flow volume (see Table 9 of text). Salt load is reduced for subsurface flow between Littlefield and Riverside. Fish are not affected by subsurface flow until it re-enters ss surface flow. If the proposed USBR groundwater barrier is not constructed, groundwater will re-enter as surface flow below Riverside, Nevada. Evaluation was made assuming all subsurface flow re-enters as surface flow. The average annual decrease in salinity is three percent for Alternative 1 and eight percent for Alternative 2. Reduction in salinity of low flow surface waters from subsurface flow re-entering is offset by increased surface flow which extends the channel length of highly saline waters. The length of channel benefitted is from the Bunkerville Diversion structure to Riverside, Nevada. ~~ :l! A-14 ,<)"" i (. ~ li'Jl.Jvd