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<br />tHlt'161 <br /> <br />Reservoir Storage <br /> <br />Reservoir storage, for many projects, is the key to the adequacy of each year's water <br />supply. The central task of Reclamation's reservoirs is to capture the spring runoff <br />for release during the dry season, But, even under the best of conditions, a multitude <br />of factors must be considered to balance reservoir storage with downstream water <br />uses, <br /> <br />Many Reclamation reservoirs were authorized by the Congress to meet multiple <br />water uses, and the requirements for each water use are balanced under the <br />reservoir's operating plan, As pertinent, the operating plans answer the following <br />questions: If carryover levels are high, how much will the reservoir need to be drawn <br />down in the winter to capture possible spring floods? Will enough water be available <br />to meet consumptive water requirements? How does the volume of water released <br />from the reservoir compare to the volume of water flowing into it? If the winter <br />snowpack is low, will there be enough water left in the reservoir pool at the end of <br />the summer season to provide for next year's water requirements? <br /> <br />At the end of water year 1989, on September 30, 1989, Reclamation knew that <br />carryover water supply in many reservoirs was dangerously low. However, the 1989- <br />1990 winter precipitation was still uncertain, In the low storage areas, if winter <br />precipitation was low, water supply would worsen; ifprecipitation was normal, water <br />supply could be adequate; but, if precipitation was higher than normal, storage could <br />be replenished while at the same time meeting water demands. The unknown <br />factor--the amount of precipitation and hence the amount of reservoir inflow-would <br />remain uncertain until well into the winter. <br /> <br />As the water year 1990 progressed, it became clear that water supplies would be <br />inadequate to meet all water-user needs in some portions of the West, Of particular <br />concern were areas of California, portions of the Colorado River basin, some <br />subbasins in the upper Missouri River drainage, and in the central Snake River <br />basin, The following maps trace the percent of normal reservoir storage as it <br />appeared at the beginning of the water year, and at four more intervals until the end <br />of the year on September 30, 1990, <br /> <br />22 <br />