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<br />, <br /> <br />million acre-feet of depletion that is disputed by the Upper Colorado River <br />Commission and the States in the Upper Basin. That limit used only because <br />there exists some physical limit of depletion and it is assumed that at <br />least that much development will occur. While depletion significantly <br />effects the production of power, affects of depletion greater that 5.8 MAF <br />won't be manifest until after the turn of the century. Depletions probably <br />will not increase at a faster rate, but they may eventually be more than the <br />5.8 MAF shown here. Our interest today is the steep part of the curve since <br />our power marketing plan is covering a period that begins in 1990. The <br />steep part of the curve represents sign i fi c ant increases in dep 1 et ions. <br /> <br />Sl ide II-4 <br /> <br />Available Capacity - Adverse Water Supply <br /> <br />With that brief background touching on the variabil ity of the water supply <br />and the changing nature of depletion planned for the Colorado River in the <br />next 15-20 years, we can estimate the dependable capacity of the power <br />plants. The capacity that would be available if the most adverse historical <br />water supply condit ions were imposed on the period 1990-1999 is shown. <br />Winter capacity values range from 1593 megawatts to a low of 1404 megawatts. <br />Summer capacity has a similar range of capacity from 1557 to 1404 megawatts. <br />These winter and summer lows resulted from the 13 year period of hydrologic <br />flow beginning in the year 1953. The average over the study period amounts <br />to 1,507 megawatts for the winter season and 1493 megawatts for the summer <br />se ason. <br /> <br />The dependab 1 e capac i ty presented in May 1980 was hi gher. That data was <br />based on the actual reservoir levels at the beginning of WY 1980. Simi- <br />larly, we have updated the study base with the actual reservoir levels at <br />the begining of WY 1982. Interestingly, Lake Powell storage at the begin- <br />ning of WY 1980 was 21,636,000 acre feet. At the beginning of WY 1982, Lake <br />Powell storage was 20,751,000 acre feet----almost 900,000 acre feet less <br />than in 1980. Dependable capacity is highly sensitive to reservoir levels. <br /> <br />Sl ide II-5 <br /> <br />Available Capacity - Lower Decile Water Supply <br /> <br />If we chose a water supply that would be exceeded 90% of the time, this is <br />the available capacity that might be expected as compared to adverse water <br />as shown on the previous slide. In this case, we find the winter capacity <br />has a wider range; a high of 1700 megawatts and a low of 1413 megawatts. In <br />the summer, about the same wide range; a high of 1702 megawatts and a low <br />of 1413 megawatts. These lows are a result of the water supply beginning in <br />1950. The low being only 9 megawatts greater than the case of adverse water <br />supply, and the high being much higher and the average being about 70 <br />megawatts higher for the winter season and 77 megawatts higher for the <br />summer season. <br /> <br />3 <br />