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<br />In May, with a heavy snowpack forecast, the reservoir is operated in accordance with <br /> <br />snowmclt criteria, with a maximum pool stage of6,920 fcet. The 1% chance rainl100d would be <br /> <br />expected to occur later in the year, between June and OClober, when Ihc lake level would be at <br /> <br />gross pool (6.924 fcet). assuming nonnal conditions. II \vas decided to simulate the 1% rainl100d <br /> <br />occurrence with the slarting reservoir storagc slightly below gross pool. <br /> <br />10.2 Jlvpolhetical Routings of J% Chance Rainl1ood. Thc 1% rainl100d computed by the <br />IIE('4I1MS model (which was discussed in Paragraph 7) from Ihe Wcsl Fork centering was used <br /> <br />as thc 1% raintlood inl10w hydrograph to McPhee Rcservoir. Thc inflow hydrograph includes the <br /> <br />concurrenl 110\\' from r.ost Canyon Creek. Routing constraints used for the simulated fIEC-5 <br /> <br />routing of thc 1% raint100d evcnt include a maximum rate of change of 1,000 cis per hour with <br /> <br />the downstrcam channel capacity of 5,000 cfs. <br /> <br />The simulation did not include diversions tor irrigation. From discussions with the U.S. <br /> <br />Bureau of Reclamation and Dolores Waler Conscrvancy District rcgarding operation of McPhee <br /> <br />Reservoir, it is assumed that. following the 1% chance general rainstornl. the \vater users would <br /> <br />be overwhelmed by local runolTand unable to handle any divcrted 110ws. In preparation for a <br /> <br />forecastcd I % chance rainl100d event, the dam opcrators would consider Ihe anteccdent basin <br /> <br />""'etncss and would closely monitor wealher forecasts. Iflhe basin were already saturated, the <br /> <br />operators would begin rcleases when the heavy rain starts. The ramping guidelines on page 2 of <br /> <br />the Fill/Spill Criteria recommend thai releascs do not increase by more than 100 cf.'i pcr hour. <br /> <br />Howcvcr, the emcrgency release critcrion is to increasc rcleascs by ",\,'hatever is necessary to <br /> <br />address the situation". In an cmcrgency siluation a channel capacity of 5.000 cis can be used, <br /> <br />although it will cause damage to picnic area structures below the dam. <br /> <br />42 <br />