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<br />o <br /> <br />Account was taken of the water losses incident to irrigation (e.g., <br /> <br />N <br />to <br />.... <br />00 <br /> <br />phreatophytes, ditch evaporation). It was assumed that such losses <br /> <br />constituted an amount equal to 10 percent of the historic irrigation <br /> <br />consumptive use. Estimated historical irrigation consumptive uses and <br /> <br />losses for each reporting year are shown on Table 1. <br /> <br />Reservoir Evaporation <br /> <br />A listing of reservoirs in the Arizona portion of the Upper Colorado <br /> <br />River Basin is shown in Table 5. Due to a lack of reservoir content <br /> <br />records, it was necessary to estimate the reservoir surface areas by <br /> <br />!!,pplying an assumed "fullness factor" against the surface area values for <br /> <br />a full reservoir. <br /> <br />Records of monthly pan evaporation at stations in and surrounding <br /> <br />the study area were tabulated. Seasonal May-October pan evaporation was <br /> <br />adjusted to annual pan evaporation and a relationship was developed of <br /> <br />annual pan evaporation versus elevation. Annual pan evaporation at each <br /> <br />reservoir site was determined using this relationship. Application of <br /> <br />the appropriate pan factor resulted in estimates of gross lake evaporation. <br /> <br />Net evaporation was computed by taking into account the precipitation <br /> <br />salvaged due to the presence of the reservoir. The net evaporation was <br /> <br />applied against the net. surface area to yield the estimates of reservoir <br /> <br />evaporation shown in Table 5. <br /> <br />Municipal, Domestic, and Industrial Uses <br /> <br />In order to estimate the municipal and domestic water uses of the <br /> <br />Navajo Nation, use was made of the approach adopted for the Upper Colo- <br /> <br />rado Region Comprehensive Framework Studies. The Indian population in <br /> <br />the Arizona portion of the Upper Colorado River Basin in 1966 was 27,772. <br /> <br />It was estimated that the per capita water consumption of the Indian <br />