OCR Text |
Show both ground and surface waters in comprehen- sive river basin programs where topography and geology indicate it to be feasible. This inten- tional addition of water to underground storage is commonly accomplished by "spreading" surplus water over permeable ground or dry stream channels overlying ground water or, less often, by injecting water into "recharge" or "return" wells. The latter method can be successfully used only where the injected water is absolutely clear. Such water spreading is now practiced most extensively in California. It is also practiced to some extent in the East and Middle West. Re- charge through wells is most extensive on Long Island, N. Y., under a requirement of State law; the quantity has reached a total of 60 million gal- lons a day In summer. During the war, strategic industries near Louisville, Ky., encountered seri- ous shortages of water for cooling purposes. The plants were designed to use water of a certain temperature, which they obtained from city sup- plies in the winter and wells in the summer. As war production needs increased, the wells were overpumped. As a partial solution, the plants bought city water during cold weather, and re- charged the wells for summer use. Ground Water Storage Ground water behavior depends largely on the thickness, extent, and three-dimensional pat- tern of the porous rocks and other permeable materials which provide the storage space for underground storage and flow of water. A sound policy of management of ground water storage must depend on adequate geological data. Typ- ical underground reservoirs may be in alluvial deposits, glacial deposits, porous sandstones or shales, or cavernous limestones. Climate is also a controlling factor. Thus, in much of the eastern half of the country, with its more plezntiful rainfall, ground water replenish- ment occurs rather frequently in most years from water which the soil is unable to hold. Over much of trie West, however, this can occur ex- tensively only during very wet years, possibly at intervals of decades. Whether in the East or the West, ground water storage, movement, and discharge fluctuate from season to season and from year to year, decreas- ing with drought and increasing with wet periods. Available records indicate, however, that such natural fluctuations compensate over the years. For this reason, in basins with large ground water storage, the impacts of drought are eased consider- ably and may be erased when precipitation is greater than average. In the West, substantial yearly replenishment occurs largely where winter-surplus water runs off from mountainous areas to permeable valley plains, and there infiltrates from streams to the underlying zone of saturation. There is also a beneficial, direct penetration of water into valley floors. In this region also, surface water stored and used for irrigation may, in part, serve to re- plenish ground water reservoirs to be pumped up for further irrigation. Here again we see the great importance of complete, unified manage- ment of the limited supplies of water. Flood flows, stored on the surface and slowly released over natural stream beds or artificial spreading grounds as clearer water, can be perco- lated to ground water. This combination has been found to offer an economical means for se- curing large storage. The importance of ground water management has been accentuated by the deep-well pump, which enables man to draw heavily from deep sources. With the increase in capacity and effi- ciency of pumps and well construction, and through uncontrolled pumping, drafts may be im- posed far greater than the safe yield of ground water. Because of its quality, temperature, low cost, and availability outside urban areas, ground water is increasingly sought for industrial pur- poses. Air conditioning has become a large ground water user in urban areas, frequently overtaxing sewers or adding temperature to the ground water where recharging wells are used. The quantity of ground water storage, move- ment, and safe yield is a problem which can only 112 |