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<br />36 <br /> <br />I <br />I' <br />I <br />, <br />I <br />:1 <br />I' <br />I <br />I <br />'" <br />I' <br />I <br />,- <br />:1 <br />I <br />I <br />I <br />I' <br />I <br /> <br />long periods of drought, will leave the reservoir with <br />too little stored water to meet all water demands. <br /> <br />Reservoir target levels for annual- ooerations. Op- <br />erations are planned each year to have 22.6 maf of <br />usable storage (reservoir elevation 3,648 ft) on <br />January 1, and have the reservoir full (elevation 3,700 <br />ft) on July 1. <br /> <br />The July target to fill the reservoir is not specified <br />directly in the CRSP Act or in other regulations. <br />Because there are areas of uncertainty regarding the <br />quantification of "602(a)" storage, a practical <br />solution to the question of minimum storage has been to <br />fill LcLke Powell each year, if possible. Thus, while a <br />strict quantification of "602(a)" storage does not <br />control the release of water from CRSP reservoirs, the <br />uncertainty over the magnitude of "602(a)" storage has <br />led to informal operating criteria which substantially <br />affect dam operations. <br /> <br />Uncertainty in annual runoff. The schedule of monthly <br />releases during the spring runoff period from January <br />through June is designed to result in a full reservoir <br />by July 1, with all releases being made through the <br />powerplant. Any increase in inflow above the forecast <br />may result in flood releases at some point during the <br />spring runoff. The design of the release schedule <br />depends -critically upon the forecast of the annual <br />inflow. <br /> <br />However, the annual inflow is difficult to predict. <br />For example, since 1922, the annual runoff in the Upper <br />Basin has ranged from 2.5 maf to over 20.0 maf. <br />Because of this uncertainty, updated forecasts of run- <br />off are made each month and the monthly release <br />schedules adjusted. Early in the annual runoff period, <br />the potential error in the forecast of the total runoff <br />is very large. Figure V-2 shows how the error, above <br />and below the projected total - runoff, is typically <br />reduced each month as forecasts are updated based on <br />information about the actual runoff. <br /> <br />Ooeratina orocedures for handlina increases in forecast <br />runoff. Under current operating procedures, any <br />increase in the forecast runoff volume is spread evenly <br />over the months remaining in the runoff period rather <br />than released immediately by increasing releases to <br />maximum powerplant capacity, until the excess volume is <br />passed. This is done to guard against making an <br />unnecessary release of water should the projected <br />