WSP08666 - Laserfiche WebLink

Home Browse Search

m co; r-. C".' ': increases in ground water depletion) are expected to outweigh the slight water quality degradation. In the absence of CAP water, municipalities would continue to expand ground water use to meet growing population demands. This would either intensify overdrafting locally, or cause use of ground water sources of lesser quality than existing sources. 5. Ground Water Model Projections Recent estimates of surface-water diversions and ground water pumping for irrigated agriculture in the CAP service area aggregate about 4.22 million acre-feet per year. Ground-water overdraft resulting from agriculture and M&I ground-water pumping presently totals about 2.2 million acre-feet (source). The effect of CAP water will be twofold: first, the enable certain existing activities, such as agriculture, to be Second, the increased supply of water will accommodate the population and economic growth without a commensurate increase ground water resources. water wi 11 continued. projected in use of Ground-water levels declines from 1923-1977 ranged from 200 feet to over 450 feet in the CAP service area (Water and Power 1979). Recently, ground water levels have been dropping 3 to 8 feet per year in the service area (Laney 1976). CAP deliveries will slow this rate of decline. DWR projections indicate that future ground water level declines will be generally 50 to 150 feet over the project period under any of the alternatives, or about 1 to 3 feet per year. In general, maximum differences among the alternative allocations are in the 50-75 foot range over 50 years for roughly half of the entities analyzed. These differences may be locally significant (see Appendix F) but overall are not considered significant. The ground water model was not run for the Proposed Acti on, since the estimated water deliveries for the Proposed Action fall within the range of Alternatives 3 and 4. Ground water response is assumed to fall within the range of those two alternatives. Of the 80+ entities analyzed, in only 2 cases (Avondale and Goodyear) is more than 50 feet of difference in future ground water declines projected between Alternatives 3 and 4. Total ground water pumping is projected to range from 60,830,000 acre-feet under Alternative 4 (Andrus Modified for M&I Use) to 68,622,000 acre-feet under No Action over the 50 year period (1985-2034). The maximum difference among the alternatives, slightly less than 8 million acre- feet over 50 years, is not considered to be significant when compared to the reduction in future ground water pumping (at least 35 to 45 million acre-feet of estimated non-Indian agricultural deliveries--see Table 1 on Projected CAP water deliveries to each category of use under each of the alternatives). :':~/:,~~:; ~ ;'y 7