An analog model of the groundwater basin of the upper Coachella Valley was constructed to determine the effects of imported water on groundwater levels. The model was considered verified when the groundwater levels generated by the model approximated the historical change in water levels of the groundwater basin caused by man's activities for the period 1936-67. The groundwater basin was almost unaffected by man's activities until about 1945 when groundwater development caused the water levels to begin to decline. The Palm Springs area has had the largest water-level decline, 75 feet Projected pumpage for the period 1968-2000 was programed on the model with the proposed recharge of Colorado River water for the same period. The model indicated a maximum water-level increase of 200 feet above the 1967 water level at Windy Point, the proposed recharge site, by the year 2000, a 130-foot increase by 1990, and a 20-foot increase by 1980. The model indicated that the proposed quantities of recharge will beneficially affect the groundwater system to Palm Desert by 1980, to Point Happy by 1990, and possibly to the Coachella Canal by 2000. The model indicated that the upper and lower valleys are within the same hydrologic system, and it has been proposed that the model be extended to the Salton Sea. On the basis of the available analyses, changes in the quality of ground water in the Whitewater River subbasin after recharge apparently will be, as a first approximation, proportional to the ratio in which the quantity of recharge and the quantity of ground water are mixed. Where mixing does not occur, the quality of the recharge water will probably not be greatly changed by ion-exchange phenomenon.

The California Department of Water Resources, through the Future Water Supply Program, is investigating the use of ground-water basins for storage of State Water Project water in order to help meet maximum annual entitlements to water project contractors. This report presents a preliminary evaluation of the geohydrologic factors affecting storage of water by artificial recharge in the upper Coachella Valley, Calif. The ground-water basin of the upper Coachella Valley seems to be geologically suitable for large-scale artificial recharge. A minimum of 900,000 acre-feet of water could probably be stored in the basin without raising basinwide water levels above those that existed in 1945. Preliminary tests indicate that a long-term artificial recharge rate of 5 feet per day may be feasible for spreading grounds in the basin if such factors as sediment and bacterial clogging can be controlled.

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The water supply for Edwards Air Force Base is ground water pumped from wells. Because annual recharge to the ground-water supply is very small, constant surveillance of the quantity and quality of the water stored in the underground basin is maintained. This report is the tenth annual inventory made in cooperation with the Department of the Air Force, The results of the current study are summarized below, "PUMPaft6 * Pumpage by the base for all uses during 1966 was about 6,280 acre-feet, most of which was pumped from the Main Base, East Camp, and North Base wells.2. Water-level fluctuations. During the period March 1961 to March 1967, four pumping depressions have formed in which water levels declined as much as 100 feet.3. Ground-water deplet ion. The estimated depletion of ground water in storage during the period April 1, 1966, to March 31, 1967, is 13,000 acre-feet. The quantity remaining in storage is about 1,300,000 acre-feet t A. Quality of water. Chemical analyses of water collected from the principal base-supply wells indicate no appreciable deterioration of the ground-water quality during the period April 1, 1966, to March 31, 1967. Because the dissolved-solids content of well 10N/9W-7A2 changes during pumping, determination should be made as to how long this well needs to be pumped to obtain potable water. Partial chemical analyses may be adequate to monitor changes in the quality of the ground water. 5. Condition of wells. Specific-capacity tests made at wells 9N/8W-6H1, 9N/9W-14P2, 9N/9W-15J1, and 9N/10W-24G1 indicate no deterioration in their condition. Specific-capacity tests should be standardized.