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l"l..... , 3 'J~' lld,- ,', / Harold E. T.. ,!Os IS? Probably 1<::5.') than olle fourth of the country has grotlllu-watcr reservoirs thOlt are permeable enough to yield water in the qUtll1tilies reC]uired hy municipal, industrial. or irrigation weIls. FUTlhennore, the soils and other rock materials above these reservoirs aTe generally not permeable enough to receive and transmit rainf:Ill as fast as it (all occur-which in one respect is fortunate because such permeability would Jluke the soil useless for agri- culture. However, in most of the country we cannot hold the raindrop where it falls. because there arc not the fllcilities for accepting and storing the water lInderg-round. Gronnd \Vater ill Isolation After we drill a well we draw water first from accumulated storage, and '....'e continue to draw from that accumulation until by the withdrawal we either induce more water to enter the reservoir or reduce the natural dislharge from the reservoir. As soon as we induce recharge or reduce discharge we go beyond the ground,water phase and affect the surface, water or soil,water phases of the hydrologic cycle, Thus if a management expert were to confine his activities exclusively to ground water, he would deal chiefly with the nonrenewable resource, and become an extraction specialist. He would have fom1idable problems, such as (a) interference, ,.....hich reduces the flow of artesian wells or increases the drawdown of pumped wells; (b) lateral and vertical movement within each aquifer, and from one aquifer to another tlnd tl1rou~h intervening- less permeable bodies; and (e) encroachment of water of inferior quality. Many of these difficulties c.ould he relieved by improving the 5p:tcing of producing wells-gcogr.lphical- Iy, in depth, and in rate of withdrawal. The management of Texas' High Plains Underground \V;Iter District tlnd tile man::lgemcl1t of well systems around Honolulu are notc'.....unhy t;}sks that arc ;.!mosl entirely grollnd-water prohlems. In most "reas, however, managemcnt restricted to ground water would be too limited in scope for optimum use even of the ground water. Organizationally, however, we can cope best with ground water as a separate entity. I\-l<lny \Vcstcrll St:1tcs reg-ubtc g-round ,vater separately from ....urface water, and Eastern St;lles arc considering separate laws for each. The title of this paper implies management especially if not exclusively of gTound water. Legally most ground water is classified as "percolating" water, which lias been defin<...>d as .....'agrant wandering drops moving by gravity hI allY and every direction along the line of least resistance," and the burden of proof is upon you if you claim that it is anything else. All this is in line with the general tendency to put ground water off in a box, all by itself. The separation of grolllld water from other w;ltcr resources has provided opportunity for specialists if! surface-waler development to ignore ground W:lter, but the adv<lntag-e was shan-lived-sooner or lCller h"'OUIHl wafe)" rose to plague them. Now the specialists in flood control, irrigation, navigation, drainage. and reservoir construction are almost universally alert to ground,water problems and to the need for data bearing upon those problems. I believe it inevitable that g-round,water data will eventually be, come an integral part also of the burgeoning smaIJ,watershed program, Interrelation of Ground and Surface vVater Eventually the withdrawals by wells are likely to change the natural pattern of flow through the ground-\Yater reservoir, either (a) by inter, (epting and diverting some water th;lt would othenvise discharge naturally ;It springs, or into s,lre.ams, or by evapotfClnspiration; or (b) by inducing