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<br /> <br />. <br /> <br />depletion at the project site. ~t is generally true for the foothills <br /> <br /> <br />region that soil moisture becomes depleted to various degrees by the begin- <br /> <br />,ning and, in particular, the end of the growing season. <br /> <br />Data describing the intake capacities of the soils on the project area <br /> <br /> <br />are also sketchy. The design memorandum numbered PC2 prepared by the U, S. <br /> <br /> <br />Army Corps of Engineers in their revised edition of August 1966 indicates <br /> <br /> <br />that the intake capacities on the area are generally high. Because of these <br /> <br /> <br />data limitations and also the limited time available for the analysis, an <br /> <br /> <br />individual storlll runoff analysis has not been completed. <br /> <br />Since the larger part of the precipitation was historically used by <br /> <br /> <br />vegetation, the method of computing effective precipitation described in <br /> <br /> <br />Technical Release No. 21 of the U. S. Department of Agriculture, Soil Con- <br /> <br /> <br />servation Service, Engineering Division, has been selected. This method <br /> <br /> <br />computes the effective part of the precipitation based on demands and on <br /> <br /> <br />availability of precipitation on a monthly basis. Effective precipitation <br /> <br /> <br />figures were computed on a monthly basis for the selected 56 consecutive <br /> <br /> <br />years. The results show that 60 to 65 percent of the annual precipitation <br /> <br /> <br />was used by the vegetation of the area and did not reach the river. <br /> <br />These results, although considered conservative, were accepted at this <br /> <br /> <br />stage of the investigation and were used to compute the net rese~oir evapora- <br /> <br /> <br />tion. It is emphasized that the effective precipitation figures obtained <br /> <br /> <br />in this computation are not accepted as final limits for the future operation <br /> <br /> <br />of the reservoir, but at that time a more detailed analysis will be conducted. <br /> <br /> <br />At this point, for the purposes of this report, the effective precipitation <br /> <br /> <br />figures are acceptable because they will result in somewhat higher evapora- <br /> <br /> <br />tion losses than expected, making the analysis rather conservative. <br /> <br />The earlier computed monthly lake evaporation estimates were reduced <br /> <br /> <br />by the monthly values of effective precipitation to arrive at the net <br /> <br /> <br />expected lake evaporation. The results of the statistical analysis of the <br /> <br /> <br />monthly net lake evaporation data are summarized in Table 2 below. <br /> <br />- 4 - <br /> <br />M. W. BITTINGER AND ASSOCIATES, INC. <br />