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<br />o 1', 1 '~8 ~ <br />U ..u G <br /> <br />mates of evaporation and change in bank storage. Lake Powell inflow <br />is estimated by taking the remaining monthly inflows from the hydrol- <br />ogy record and applying a forecast error term composed of both random <br />and deterministic components. Lake Mead EOWY contents are predicted <br />by balancing current contents, Powell releases (Mead inflows), Mead <br />releases, and estimates of evaporation and change in bank storage. <br /> <br />Total upper basin predicted contents are computed by adding the <br />current contents of Flaming Gorge, Blue Mesa, and Navajo Reservoirs <br />to the predicted EOWY contents of Lake Powell. <br /> <br />8.2.4 602(a) Storage <br /> <br />Section 602(a) of Public Law 90-537 contains provlslons for the <br />storage of water in reservoirs of the Colorado River Storage Project <br />and for release of water from Lake Powell in a specified priority. <br />Generally, section 602(a) provides that water not required to be <br />released from Lake Powell as part of the annual objective minimum <br />release shall be stored to assure future deliveries to the Lower <br />Basin without impairing annual consumptive uses in the Upper Basin. <br />It further provides that water not required to be stored for this <br />purpose shall be released from Lake Powell to either maintain, as <br />nearly as practicable, active storage in Lake Mead equal to the <br />active storage in Lake Powell, or to avoid anticipated spills from <br />Lake Powell. The term "602(a) storage" refers to the quantity of <br />water required to be in storage in the Upper Basin so as to assure <br />future deliveries to the Lower Basin without impairing annual con- <br />sumptive uses in the Upper Basin. <br /> <br />The CRSM, in determining 602(a) storage, considers all relevant fac- <br />tors i nc 1 udi ng, but not limited to, (1) hi stori c streamfl ows, (2) the <br />most critical period of record, and (3) probabilities of water <br />supply. In order to apply the conditions imposed by section 602(a) <br />of Public Law 90-537, certain quantifiable assumptions are made by <br />the CRSM. Those asssumptions are as follows: <br /> <br />1. An annual release of 8.23 million acre-feet from Lake Powell <br />satisfies the Lower Basin delivery requirement. <br /> <br />2. The 602(a) storage is determined without using the volume of <br />water below minimum power pool elevation in the Upper Basin reser- <br />voirs or without using the volume of sediment accumulated above <br />minimum power pool elevation. <br /> <br />3. The critical drought period is the 12-year period of natural <br />flows from 1953 through 1964. <br /> <br />4. Annual shortages in the Upper Basin are assumed to be <br />6.12 percent of the total demand. This represents zero shortage <br />on 2.1 MAF of M&! uses and 10 percent shortage on 3.7 MAF of irri- <br />gat i on uses. <br /> <br />36 <br />