Laserfiche WebLink
<br />0" -:- 'joQr <br />U .1,-"-",,, ~ <br /> <br />. <br /> <br />... <br /> <br />Water is commonly referred to as a renewable resource. strictly <br />speaking, this is true. Howevp-r for marw ground-water reservoirs, <br />especially those in the arid and semiarid parts of the country, the <br />question of renewalxi.lity is academic so far as the lUe span of <br />present vater users is concerned. Even in hwnid areas, ground water <br />withdrawn from wells is ren8llable by natural recharge only where the <br />wells are so placed that natural discharge is reduced or natural <br />recharge increased by an amount equal to the net conswrrptive use. <br />If the wells cannot be ideally located--or, even if they are but <br />the net consumptive use of water exceeds the natural discharge <br />(recharge) of the aquifer--then the reserve can be renewed only it <br />the withdrawals are reduced or stopped. <br /> <br />'v <br /> <br />Year-to-;rear decll.nes in water level are t.he usual condition in <br />many of the developed aquifers of the West. Persistent declines are <br />evidence of depletion of ground-water resources. Whether the <br />depletion is localized or aquifer-vide, and whether it is temporar,r <br />or will persist for periods equal to or greater than long-tem climatic <br />cycles, deperxls upon the local geo~drologic situation. lowering of <br />water levels is a natural consequence of pumping of wells, so that even <br />in hUlllid areas of abundant recharge there are declines ot water level. <br /> <br />In areas of shallow-1Jj.ng ground water, particularly in malY <br />stre8lll valleys of the West, rank growths of phreatophytic vegetation <br />consume large quantities of water. The area of phreatophytes 1n <br />California, Arizona, New Mexico, Nevada, Utah, and Colorado currently <br />is estimated as 7 million acres. These plants consume 10 to 12 <br />]1111lion scre-feet a year. The area of phreatophytes in New Mexico <br />am Arizona is almost 1 mUlion acres, and the water consumption is <br />2t to 3 ndllion acre-feet per year (U. S. Senate Select Committee on <br />National Water Resources, 196ob, p. 2). Not only do these plants <br />waste large amounts of water, but the water trBllSpired ill virtually <br />pure. The chemical character of the water remaining therefore hell <br />deteriorated. Salvage of thil9 wasted water by such measures as <br />eradication of the vegetation and construction of draiIUl is o~ <br />partially effective. However, in many areas capture of this wasted <br />water could be easily accomplished and would be a natural consequence <br />of the lowering of water levels caused by pumping. If wells are <br />located with the objective of salvaging water, then the net usable <br />supply can be increased end the quality improved. However, if wells <br />sre installed with water supply as the only objective, then their <br />location IDay be such that the pumped water comell from ground-w&.ter <br />storage or from streamflow. If so, the individual well owner <br />benefits temporarily at the long-term expense ot all water users. <br /> <br />Use of ground water may provide an increase in water supply <br />through the mediUIII of' recirculation. This is particularly true in <br />irrigated areas, where a significant portion of the water applied to <br />the cropll may infiltrate to the ground-.ater bo~. It is then pUlllped <br />to the land surface for reuse by the same individual or his neighbors. <br /> <br />:3 <br />