Laserfiche WebLink
<br />. <br /> <br />. <br /> <br />w <br />00 <br />.+:0- <br />N <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />encompasses most of the southern half of Arizona. Annual undepleted runoff <br /> <br />varies from as much as 8 inches in the headwater areas to O. 1 inch or less <br /> <br />in the deserts. Almost all available surface water is utilized within the <br /> <br />subregion, and outflows from the Gila River to the main Colorado River at <br /> <br />Yuma are now insignificant. The Salt and Verde Rivers produce about 70 <br /> <br />percent of the surface water supplies of the subregion, and six major <br /> <br />reservoirs on these two streams control the runoff. Most of the remaining <br /> <br />surface runoff within the subregion is produced by the Gila water shed above the <br /> <br />Ashurst-Hayden diversion dam. In the lowlands much of the desert precipitation <br /> <br />is consumed rapidly by evapotranspiration. <br /> <br />Groundwater supplies in the subregion are extensive and generally <br /> <br />are of good quality. Current groundwater pumpage exceeds surface water <br /> <br />diversions by several times, and now stands at about 4.5 million acre-feet <br /> <br />annually. These withdrawals have produced an overdraft which is estimated <br /> <br />to be more than 2.5 million acre-feet annually. This large overdraft is <br /> <br />causing rapidly declining groundwater levels, land subsidence, increased <br /> <br />pumping costs, and some degradation of water quality. <br /> <br />BASIN DEVELOPMENT AND MANAGEMENT <br /> <br />Superimposed on the natural physical system is the use and <br /> <br />management of the lands which comprise the watersheds of the Colorado <br /> <br />River. Man's activities on these lands and the water which is diverted from <br /> <br />the river system to sustain these activities serves to change and modify <br /> <br />the water quality of the natural system. <br /> <br />23 <br /> <br />,I,., <br />