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<br />OOl?!'O <br /> <br />Summary of Differences CRSS vs. CRSP <br /> <br />The following are the major sources of additions 1 water in CRSS: <br /> <br />1. Undepleted inflow above Lees Ferry--about 227,000 af per year. <br /> <br />2. Scheduled demands which go unsatisfied in CRSS--about 200,000 af per <br />year. <br /> <br />3. Differences in the Parker to the Imperial reach losses or gains <br />attributable to unidentified and unmeasured return flows as assigned in the <br />CRSP model--about 130,000 af per year. <br /> <br />4. Differences in the Parker to the Imperial reach losses or gains <br />attributable to both past and future reductions in phreatophyte consumptive <br />use in the CRSS model--260,000 af. <br /> <br />The following are differences in simulation model mechanisms that result in <br />more water being delivered to CAP in CRSS: <br /> <br />1. The "602a" storage rule curve in CRSS required equalization releases <br />more frequently than did CRSP's. <br /> <br />2. A water shortage <br />was below 1095 feet. <br />1124 feet. CRSS also <br />occur. <br /> <br />determination in CRSS only occurred when Lake Mead <br />CRSP imposed shortages when Lake Mead fell below <br />delivered 50,000 af per year more when shortages did <br /> <br />There are numerous other minor differences; however, these are relatively <br />insignificant in comparison with the major differences. Under the heading <br />of minor differences, for purposes of this comparison, would be factors <br />such as: reservoir contents at the beginning of the study, flood control <br />criteria, surplus water supply decision criteria, and CAP delivery <br />capability in the early project stages. - Also, it should be noted that <br />since the data and assumptions change routinely, some of the differences <br />noted in this comparison would vary somewhat if other studies were used for <br />comparison. The demand data base is frequently updated, for example. <br />Future changes to either the data or operating assumptions could <br />significantly affect the projections of CAP water supply. Nevertheless, <br />much of the increase in yield to CAP produced by CRSS can be attributed to <br />the characteristics of the model and its hydrology data base. These are <br />not so subject to change. Two future changes to the hydrology data base <br />will probably further increase CRSS estimates of CAP yield: (1) the <br />addition of hydrology data below Imperial Dam and (2) the addition of water ,i,:, rC <br />years 1984 and 1985 to the data set. On the other hand, the identification c,,:,'~,r (". <br />and accounting of unmeasured return flows in the Lower Basin could tend to ,,', ,c~ ,'" <br />reduce projections of CAP yield. '~~i(""j <br /> <br />In summary, the difference in CAP yield, as estimated by CRSS versus the <br />old CRSP model estimates, is explained by differences in the data bases and <br />simulation methodologies. However, because CAP yield is the most sensitive <br />operational parameter, it can be expected that future modifications to the <br />models and data base will continue to affect CAP's water supply. <br /> <br />5 <br />