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<br />- <br /> <br />pumped water results in either diJIlinution of atrelllllfiow or reduction <br />in ground-water storage, or both. Before pumping is undertaken in <br />most such stream valleys, ground water feeds the streams. After <br />pumping lowers the water table the ground-water accretion to the <br />streams is reduced or, DIOre frequently, the gradient of the water <br />table is reversed so that the stream loses rather than gains water. <br />Water shortages downstream are thereby increased, and individuab <br />downstream who are able also install wells to satisfy their water <br />needs. Because of this extraction from storage, the stream will <br />continue to lose water even atter nonnal inflow to the valley is <br />resumed. Therefore, pumping will be continued until such time 88 <br />increased efficiency in water use, reduction of noribeneficial losses, <br />and inflow of excess surface water result in repleniShment of ground- <br />water storage. <br /> <br />A study of the effects of pumping in the Rincon and Mesilla <br />Valleys of the Rio Grande in New Mexico showed that pumping would <br />need to be continued for 4 years atter a return to nonnal surface <br />supply following a 5-year period of 5o-percent-normal surface supply. <br />In the absence of excess surface water, pumping there would need to <br />be continued, even in years of nonnal surface supply, unless the <br />debt to ground-water storage could be gradu~ reduced by more <br />efficient use of the pumped water and the reduction in pmnping that <br />would be made pOSSible. It was shown that ground water obtained by <br />pumping in the Rincon and Mesilla Valleys (where losses from areas <br />of native vegetation are small) does not represent an additional <br />supply or new source of water, but rather a change in method, time, <br />and place of diversion of the supply already available (Conover, 1954, <br />p. 2, 122, 126). During the period of shortage of project water <br />supply in the surface reservoirs, individual fanners utilized the <br />ground-water reservoir by pumping of wells. As a natural consequence <br />the ground-water reservoir was replenished later from project water <br />supply by stream losses and infiltration from irrigated lands. Pump- <br />ing in such circumstances therefore is, in effect, borrowing on <br />future water supplies. <br /> <br />',. <br /> <br />This unplanned, though sanewhat effective, use of the ground- <br />water reservoir in conjunction with the surface stream benefits those <br />who have wells but works a hardship on those who have only surface- <br />water rights. Planned de~lopment and management of ground water in <br />streBll1 valleys can increase the water supply by salvaging nonbeneficial <br />losses in areas of shallow water and will facilitate using the ground- <br />water reservoir in conjunction with the surface supply to the maximum <br />benefit of all water users. Such planned development and management <br />necessitates locating and pumping of wells in hannolV with the surface <br />system. If such is properly done a perennial water supply can result. <br /> <br />8 <br /> <br />.' <br />