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<br />In the summer, planL" and trees use up most of
<br />thl:' rainfall, by transpiration through their leaves.
<br />Only \'Cry hea,")" rainstonns are likely to recharge
<br />ground-~'ater ~r'\'oin; durinA' the !':Towing sea-
<br />~n; thus th(" ""a1ef table usually declines durinA'
<br />that season. If thr-rc arT hea,')' rain... in the fall,
<br />the water table will ri~ again. although not usu.
<br />ally as high as in the .spring-. The .....ater table
<br />gradually ..inks during the winter, and f("aches a
<br />10..... point in the spring' jlL"t bdore the mow and
<br />ice thaw and the spring rains lx-g-in. The pattern
<br />is somewhal similar in the humid Soulhea."t and
<br />South. except Ihat there is no snowmelt, and re-
<br />charge must depend on rainfall. Floods and re-
<br />charge thus may occur in the winter. In arid
<br />arl"a5 of the United Statr:s, ground,w~ler fC.
<br />charge from rainfall is similar except that it may
<br />be very low or even nonexistent. \\"estem aqui.
<br />fers depend largely on recharge from streams that
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<br />carry rainwater and snowmdt from the moun-
<br />tains.
<br />Gound-water r~r"'oirs can ~ recharged arti.
<br />ficially (figs. 10, II). This techniquc-, first used
<br />in Denn'r in 1889, ha.'i been adoptc-d in some other
<br />parts of the count!)., (':S~dally in California. In
<br />Ihe Long Island area of Xc-w York City, consid-
<br />erable ground walc-r used for air conditioning i3
<br />returned to the ground through wells. Some
<br />attempl" to r<<harge a ground-water re."Cn'oir by
<br />artificial means haw failed. There is still a lot to
<br />be learned about this technique and how or why
<br />it succeeds aT fails.
<br />There aTC two chief ways of anificially ~-
<br />charging ground-watc-r ft<;("n'oirs. One is by
<br />spreading water o\"er the land through a spread-
<br />inA" ground or through pit~. furrows, or dilehcs.
<br />This method is use-d in Ihe Central Valley of Cali-
<br />fornia and in Peoria, lII.. among other area,>.
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<br />19
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