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<br />III - I <br /> <br />SECTION III <br /> <br />HY DROLOGIC ANALYSES <br /> <br />FLOOD HY DROLOGY <br /> <br />Hydrologically, the basin may be divided into two areas with <br />Eldorado Springs as the boundary between them. Stream flows from the <br />mountain terrain are greatly affected by Gross Reservoir. This Reservoir <br />collects and stores west slope water which is imported through the Moffat <br />Tunnel. The water is released from Gross Reservoir into South Boulder <br />Creek and diverted into the South Boulder diversion canal. The intake for <br />the canal is located about three miles upstream from Eldorado Springs. <br />According to the Denver Water Department, the normal operation pattern <br />consists of filling the reservoir during the Spring runoff period and gradu- <br />ally drawing it down over the remainder of the year. There is a limited <br />amount of flood storage in the reservoir. The narrow canyon and the water <br />supply characteristics of the project dictates that the reservoir cannot be <br />expected to store significant amounts of flood water. However, considerable <br />attenuation of peak flows could be caused by the presence of the reservoir <br />during flood periods. It must be recognized that the reservoir could be full <br />at the time of a major storm. As a consequence, the flood protection bene- <br />fits of the reservoir would be limited. The Denver Water Department's <br />policy for the operation of the reservoir is shown in Appendix 1. <br /> <br />Based on the analysis of this operating policy and historical records, <br />it was assumed that there would be significant regulation by Gross Reservoir <br />so that a flow of 300 cfs would be released from it during a 100-year fre- <br />quency storm. <br /> <br />Design rainfall for the 5-, 25- and 100-year frequency storms were <br />taken from tables in a Project REUSE report prepared by Leonard R ice Con- <br />sulting Water Engineers. These figures are shown in Table I on the follow- <br />ing page. <br /> <br />