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<br />o <br />c.:) <br />Co!.) <br />C) <br />CJI <br />(;() <br /> <br />I <br /> <br />There are no records of reservoir storage, diversions, or return flow <br /> <br />that could be used to compute consumptive use on an inflow-outflow basis. <br /> <br />Consequently, it was necessary to estimate the historical irrigation consump- <br /> <br />tive use by using empirical consumptive use formulas with historical climatic <br /> <br />data as input. The potential irrigation consumptive use was computed using <br /> <br />the modified Blaney-Criddle formula. <br /> <br />The irrigation projects are subject to chronic water shortages. Some of <br /> <br />the projects (notably many farms) have storage reservoirs and thus receive a <br /> <br />somewhat assured water supply. The remainder of the projects are dependent on <br /> <br />diversions from summer aod fall thunderstorm flood runoff. Thus, full pot en- <br /> <br />tia1 consumptive use would be realized only in occasional very wet water years. <br /> <br />'Examination of the precipitation and runoff records indicate very favor- <br /> <br />able water supply conditions in April and May, dry conditions in June and July, <br /> <br />and near to above normal precipitation and runoff in August and September. On <br /> <br />this basis it was assumed that the irrigated lands received only half of a full <br /> <br />supply so a factor of 50 percent was applied to the theoretical comsumptive use <br /> <br />results. <br /> <br />Account was taken of the water Losses incident to irrigation -(e,g. t <br /> <br />phreatophytes, ditch evaporation). It was assumed that such losses consti- <br /> <br />tuted an amount equal to 10 percent of the historic irrigation conf,umptive <br /> <br />use, Estimated historical irrigation consumpt ive uses and losses are shown on <br /> <br />Table 1. <br /> <br />Res~rvoir Evaporation <br /> <br />A listing of reservoirs ln the Arizona portioo of the Upper Colorado River <br /> <br />Basin is shown in Table 4. Due to a lack of reservoir content records, it <br /> <br />was necessary to estimate the reservoir surface areas by applying an assumed <br /> <br />"fullness factor" against the surface area values for a full reservoir. <br />