AZ vs. CA:24 California Exhibits, Vol. XXIV; Miscellaneous

page 37

PROBLEMS OF IMPERIAL VALLEY AND VICINITY. 37 Table No. 9.-Averages 1903-1920. Acre-feet. Average discharge of Colorado at Yuma, 1903-1920..................... 17,400,000 Diverted above by Yuma project.......................«...-----.'.----- "150,000 Total discharge............................-.................... 17,550,000 Discharge of Gila............................___.................... 1,080,000 Estimated at Boulder Canyon.............________.............. 16,470,000 Past depletion '...............................,............-----.-----.. 560,000 Remainder at Boulder Canyon..............................-----,. 15,910, Q00 Future depletion: Development, upper basin.............................. 4,230,000 Reservoirs in canyon section................fiL-i........2,070,000 ----------- 6,300,000 Remaining water.............................................. 9,610,000 The above table is for the years 1903 to 1920, which leaves out the low cycle preceding. However, it is probable that no reduction in. average amount of water would result if that period were taken into the cycle because consumption would be less in the upper basin and evaporation less in the regulating reservoirs along the river. At Boulder Canyon, for instance, the reservoir contents would be so depleted that the average submerged area would be about 60 to 70 per cent of that normally submerged. DEMANDS ON WATER SUPPLY. The demands on water supply at Boulder Canyon will be for irrigation of the entire irrigable area below, both now irrigated and estimated additional, plus evaporation from reservoirs at Boulder Canyon and below. This last itern^ has been already used in estimating the water supply in the previous computation so that only irrigation demands remain to be considered. Data at hand indicate that water consumed annually in Imperial Valley for crop growth averages somewhat less than 3 feet in depth. Hence, if conditions were favorable for reuse of return flow, there is enough water for approximately 3,000,000 acres. But conditions are not favorable for reuse of return flow at least by-diversion from the river as, after Laguna Dam is^passed, most of« the irrigable land does not slope toward the river. In the Imperial Valley there should be some dependable seepage or return water in the drainage channels and perhaps some surface water which can be reused, but because of the peculiar topographical features of the region this will be comparatively small. The following assumptions are made: Annual gross demand for irrigation, gravity, 4.40 acre-feet per acre; pump, 3.50 acre-feet per acre. Annual,net demand above Laguna Dam, consumptive use, 3 acre-Teet per acre. 1 Less than given in previous estimates, because embracing a shorter period of time.