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into the southern California basin through the California Aqueduct and the Los Angeles Aqueduct, by the salvage of water along the Colorado River between Hoover Dam and the Mexican border, by increased ground-water recharge as a result of the water imports, and through the implementation of programs of water reclamation. Resolution of the problem of unauthorized diversions totaling about 200,000 acre-feet annually by trespassers along the Colorado River could further increases the supply available for use. It is also estimated that present water requirements will increase from about 17.7 million acre-feet per year to about 20.1 million acre-feet per year by 1975, as shown on table 13. On the basis of population projections and limiting irrigated acreage to its present level, it is estimated that by accomplishment of programs for importing water from northern California to the Pacific Southwest, and through water salvage and water reclamation programs within the basin, the estimated shortage would be about 2.2 million acre-feet per year by 1975. This imbalance would increase progressively in future years as a result of the increasing water demands of the growing population and the decreasing water supply in the Colorado River resulting from progressively increasing depletions by the Upper Basin States. The apparent water-supply deficiency, indicated as about 2.2 million acre-feet per year in 1975, and increasing to almost 5 million acre-feet per year by the year 2000, is shown on table 16. The estimated quantities of water available at and below Hoover Dam to the year 2000 are shown in table 16A. No attempt has been made in the present analysis to identify the shortages by States or other geographic areas, since it is the purpose of this report to treat the Pacific Southwest as a single region with common water problems. This deficiency can only be met by fully implemented programs of water management, plus the further import of water from water-surplus areas outside the Pacific Southwest region, or by the desalting of sea water and brackish waters in the area, or by a combination of the two. It is apparent, however, that by far the greater part of the water shortage that now exists is represented by the ground-water overdraft in central Arizona. It appears probable that this present shortage can be partially off set through the import of Colorado River water under Arizona's apportionment under the recent Supreme Court decision. Such a large-scale diversion by the Central Arizona Project would, on the other hand, be at the expense of California which is now diverting, through presently constructed facilities, water which the Supreme court has allocated to Arizona. It is for this reason that water-resource development planning must be carried forward in the future on a regional, rather than a local, basis. The specific problems of each of the affected States of the Lower Colorado River Basin must be consolidated through comprehensive planning which will prevent the solution of one area's problems at the expense of another area. IV-10Epson Perfection 4870 Photo, 400 dpi, 8 bit, 14,295,040 byte