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<br />-16- <br /> <br />consumptive use and outflow. The most probable explanation <br />for this discrepancy either lies in inadequate or unreliable <br />data used to determine watershed yie~d, a hydraulic or <br />leaky connection between the first confining layer and the <br />artesian aquifer, a greater degree of recirculation than <br />was originally thought, or a combination of these factors. <br />The proposed plan of operation for the project envisions <br />the lowering by pumping of the shallow surface aquifer to a <br />depth of 8 feet below the ground surface so as to effectively <br />eliminate evaporation and plant transpiration from all but <br />the deep-rooted plants. It also proposes to intercept sur- <br />face runoff into the Basin. The amount of water that can <br />be salvaged annually by lowering the water table is largely <br />dependent on the natural depth to water before drainage. <br />Contribution of Surface Water <br />Consumption of natural rainfall occurs regardless of <br />the depth of water table and under San Luis Valley conditions, <br />it seems reasonable to assume that substantially all precipi- <br />tation falling on the Valley floor will be consumed where it <br />falls. The principal exception will be that precipitation <br />which falls during cloudbursts, of which a portion will reach <br />the sump and thalweg areas as flood flows. <br />The U.S.B.R. estimates that 15,000 acre-feet of water <br />can be derived for Compact make-up dUring the average year <br />from surface sources. This, in our opinion, is somewhat <br />optimistic inasmuch as facts would indicate that a considerable <br /> <br />r ''. "4 u^ 0 <br />\." t..i C _ <br />