WSP01381 - Laserfiche WebLink

Home Browse Search

. . 2 '-::> have the effect of decreasing the average yield over the draW-down period by less than 600 acre feet per year. Since CRSS rounds much of Its output data to the nearest 1000 acre feet and the yield has been reported to the nearest iO,OOO acre feet, it was felt that the change was not significant and was dropped from further consideration. (,.;, CJ' " ,~ Q Power Pool/Inactive Pool Utilization It was thought that by changing the Input information to CRSS that the reservoirs could be drawn-down below minimum power or Into Inactive pools and that subsequent runs would indicate the amount of storage to be used for a mass balance analysis. It was found, however, that ChilT'qes wouldl1ave to l>emade to the model code Itself In order for the reservoirs to draw-down below establishj!d minimum elevations. In the Interest of time, approximations were made as described below to determine the amount of storage applicable to a mass balance analysis. In the previous analyses, the amount of storage was determined from the amount of total storage available at the beginning of the drawdown period less the inactive capacity , remainln.g at the end of the drawdown period. This was 27.774 MAF- 3.0i2 MAF or 24.762 MAF. As explained in the previous write-up, this was then adjusted for use In a mass balance analysis using annual data. This adjustment was made for both streamflow and storage amounts which occurred beyond the even annual Increments and was reflected solely in the adjusted storage figure. The resultant adjusted storage was 20,197 MAF, In tl\e current analysis i~ was assumed that all of the inactive pool water would be available for use and that the total amount of storage water available for the drawdown period would be 27.774 MAF. The same adjustment was then applied to this figure. Implicit In that is the assumption that ,the length of the drawdown period wouIl!!::e ,the ,same as !n the pr~viousanal}}sis. While CRSS runs, had they been made, would have confirmed this, oUr experience would indicate that this Is a valld assumption. The adjustment applled to the total storage was as follows: 24.774 x 25 - 4.000 = 23.141 MAF 25.5833 Utilizing this value in the mass balance procedure along with a minimum release of 8.23 MAF at Glen Canyon produces a firm yield (no shortages) of 5.67 MAF for the upper basin. The results of additional analysis which relate yield to basin wide shortages and the probability of meeting a yield given a particular shortage are shown in Figure 1. Because the data are somewhat limited, it should