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<br />-~ <br /> <br />1IO~ 89 '3 <br /> <br />. <br /> <br />. <br /> <br />The CRSP model inflows for the Parker to the Imperial reach <br />accounted for only a small amount of water salvage due to past phreatophyte <br />removal, and none in the future. The net effect was to reduce average <br />annual reach loss by only 12,000 af. Thus, the difference in estimates of <br />water saved from reduction in phreatophyte consumptive use accounts for a <br />major part of the hydrologic difference in the Parker to the Imperial <br />reach. The difference of 293,000 af cited in the summary table would have <br />been even greater had the CRSP average reach loss been based on data that <br />included the 1935-1962 period. <br /> <br />The reach below Imperial Dam is not a source of additional water <br />in CRSS. Since CRSS does not employ any hydrology data downstream of the <br />Imperial Dam, inflow is zero. The CRSP data showed an average of <br />162,000 af of inflow per year in this reach. When the CRSS data base is <br />completed for this reach, we may expect it to be a "gaining reach," that <br />is, a source of additional water. <br /> <br />2. Mechanisms in CRSS which Enable More Water to Reach Lake Mead and Then <br />be Delivered to CAP <br /> <br />a. "602a" Storage Determination. <br /> <br />In CRSS, the study used for this comparison simulated the "602a" <br />storage requirement by determining what amount of Upper Basin storage would <br />be required to deliver 8.23 million acre-feet (maf) per year to the <br />Lower Basin over a reoccurrence of the 12-year drought period of 1953 <br />through 1964, while still maintaining a minimum generating head at the <br />Glen Canyon Dam. Projected depletions and sediment accumulations are <br />considered in making the determination. <br /> <br />The CRSP study used for comparison did not equalize storage at <br />all after 1993 because the estimation of "602a" storage exceeded the total <br />storage capacity of the Upper Basin reservoirs after 1993. The CRSS study <br />has occurrences of storage equalization releases throughout the study. <br /> <br />Some of the "storage equalization" releases would have to be <br />spilled eventually anyway, but they are undoubtedly a mechanism which, on <br />the average, releases more water into Lake Mead in the CRSS study. <br /> <br />~ b. Criteria for Determination of Water Shortage Situations. <br /> <br />~~ ~ The CRSP study reduced CAP diversions to 400,000 af per year when <br />L\~~'~ Lake Mead fell below 1124 feet. CRSS reduced CAP diversions to 450,000 af <br />/~\G{~ per year when Lake Mead fell below 1095 feet. This difference in decision <br />U ~\fJ',,( criteria enabled a full supply to be delivered to Arizona more frequently <br />(If ~~:n us~ng the CRSS model. When shortages did occur, CRSS delivered <br /> <br />l~~'~~ more. <br />'?f~~.. ~~ <br />'\.~r' <br />'Jfl <br />~ <br /> <br />4 <br />