WSP07779 - Laserfiche WebLink

Home Browse Search

. j ~ ALTERNATIVE 8 DOWNSTREAM MAIN STEM STORAGE Mainstem storage has been proposed for the lower South Platte River down- stream from Greeley, One of the prim- ary purposes of downstream main- stem storage would be for irrigation, either of new lands (sub-alternative 8a), or to supplement already irrigated lands (sub,alternative 8b), Other con- siderations would be possible water supply to future municipal and indus- trial demands, and reduction of sea- son and year-ta-year flow variations in the river downstream from Fort Morgan, The proposed Narrows Reservoir. a downstream reservoir: has be~n designed with a total storage capacity of 973,000 acre-Ieet. The proposed storage reservoir would deliver an estimated 120,000 acre,feet (new lands, 8a) or 93_000 acre-Ieet of sup- plemental (8b) water annually, Evaluation The market-valued outputs of the first sub-alternative (8a) would be irriga- tion water. hydroelectric power, flood protection and recreation. Net annual economic benefits are estimated to be $1.9 million, This amounts to a 0,3 percent rate of return on the required investment of over $571 million, The market-valued outputs of the second sub-alternative (8b) would also be irrigation water, hydroelectric power. flood protection and recrea- tion, Net annual economic benefits are estimated to be $4.1 million, This amounts to a 2,8 percent rate of return on the required investment of over $144 million, The relocation of approximately 825 residents from the communities of Weldona, Goodrich and Orchard to accommodate the proposed reservoir would result in employment changes. It would also have an impact on school districts, law enforcement, health ser- vices and housing in the vicinity of the project. The proposed Narrows Reservoir would contain 475,000 acre-feet of I*~ I ~. . - .~ . )E RJ~!~~Q'\e BALZA)f )ORCH~~f~I~~W~~~~ -A'" rl -~ETT~ ~ -->..r I ' 'r 4 i (' · /' MOkGAf' i ;-/\ \ ~i (ilt \~I .... ) storage capacity for flood control and 75,000 acre-feet of joint,use (irrigation and flood control) capacity to be reserved when the potential for flood- ing is high, Only the reach of the South Platte River downstream from Wel- dona would receive flood control benefits. Narrows Reservoir could also provide 13.200 acres of surface area at the top of the conservation pool. increasing available recreational activities in adjoining counties, Studies have presented conflicting evi- dence about other impacts of a reser- voir on water quality conditions downstream from the reservoir. The U,S, Department of the Interior esti- mated that water released from the re- servoir would have smaller dissolved solids concentrations, on the average, than under present conditions, The reservoir would also reduce sus- pended sediment concentration of flows in the downstream reach. The temperature of water released from the reservoir would tend to be mOTe uniform seasonally, -~-l A U.s, Geological Survey study esti. mates that dissolved solids concentra- tions in streamflow may increase significantly during high flow condi- tions but decrease during low flood conditions if a downstream mainstem reservoir were constructed on the South Platte River, These changes would be due to a combination of increased evaporation losses due to operational release schedules. and to the increased consumptive us~ of irri- gation water downstream. The major impact on fish would result from the change of a reach of the South Platte River from a flowing stream habitat to a lake habitat. The inundation of 14,900 acres probably would also result in the loss of wildlife habitat. A hydroelectric power component has been included with the proposed Narrows Reservoir, even though it is not currently a part of the authorized federal project. The hydroelectric power component would have the capacity of 1.6 megawatts, 9