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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />1 <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />3.3 Outlet Works <br /> <br />Following a review of the hydraulics of the existing outlet works; two <br />criteri a were eval uated. These i ncl uded: 1) the capacity of the outl et <br />works to release the max imum fi ve feet of storage at a rate of one foot per <br />day and 2) the outlet capacity with regard to the normal flow. <br /> <br />The main outlet works discharge rating curve, as developed by the Greeley City <br />Engi neer, was revi ewed and found to be acceptabl e. Thi s curve is i ncl uded in <br />Figure V.5. <br /> <br />The State Engi neer requi res that the outl et works have the emergency capacity <br />to release the maximum five feet of storage at a rate of one foot per day. <br />The net storage in the fi ve feet below the normal water surface (el evati on <br />9295) is approximately 108 acre-feet. From the outl et works stage-di scharge <br />curve, at an average elevation of 9292.5 (16.6 feet gage height), the computed <br />di scharge is 45 cfs. Thi s is equi val ent to a vol ume of 446 acre-feet for a <br />five-day period. Therefore, the outlet works is capable of discharging the <br />maximum five feet of storage in less than five days, assuming there is no <br />additional inflow into the reservoir. <br /> <br />Twin Lakes Reservoir is currently restricted to zero storage volume. <br />Therefore it is not necessary that the outlet works has the capacity to <br />maintain the water surface at a particular elevation. However, it must still <br />be demonstrated that the outlet works has the capacity to discharge the normal <br />flow. Although no discharge measurements have been made at Twin Lakes <br />Reservoir, measurements are available at a gaged site, representing a similar <br />basin of equivalent size. U.S.G.S. discharge measurements at Little Beaver <br />Creek near Idylwilde, are available for the period 1961-1973. Review of these <br />records showed June to be the month with the highest average discharge; For <br />the 13-year peri od, the average monthly di scharge for June was 7 cfs; as <br />computed from a 30-day total of 404 acre-feet. The range over the period went <br />from a low of 4 cfs (213 acre-feet) to a high of 10 cfs (587 acre-feet). The <br />outlet works has the capacity to discharge the average June flow of 7 cfs; as <br />well as the maximum average June flow of 10 cfs, with less than 2 feet of head <br /> <br />-60- <br />