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;IJ 1380 188 f~sJenti(/ls for O/Jtimllrn Use of Grollnd-, er Resources recharge by making space available for it, as for example by wells along rivers. The increased recharge Of decreased natural discharge is an indica- tion of the extent to which the wells have modified the hydrologic cycle; to that extent tIle wells draw upon a renewable resource. Concurrently. of course. they may be depleting the nonrenewable, accumulated reserve. A well may modify the natural discharge or recharge in a few hours of pump- ing; at the other extreme, a large group of wells may withdraw accumulated reserves for years without making any measurable change in either natura] rtdlarge or natuf<lI discharge. \\Then wells by pumping achieve a reduction in the naturtll discharge. the change may be wholly beneficial to society. as for example where the natural <lisch:nge wouln have w;lsted to the ocean or to the 31111o.sphcrc; but it may reduce tile now of springs or the base nm.... of stream..... or lower the w;ttcr table, to the detriment of people who might other"wise h.1l'e used the water as it Was discharged naturally. Similarly. increasing the recharge to a ground-water reservoir may be entirely beneficial or it may be detrimental to the interests of others who could have used the water. The question of optimum lIse here transcends the confines of the grollllrl-wattT reservoir aIld even the physical potelltial...; of 'Wil[er supply. and hecome'')' ~l vH:ial. ecollomic, and legal problem, . Examples are numerous of tlle effects of }JulIlping from wells upon water supplies that had long been used by others: the drying up of large spring' neJr Fort Stockton, Texas; the lowering of the water whle below subirriga- tion level in the \Virhita, Kansas, lrell field; the reduced now of the J\Jad River through Dayton, Ohio, beca",e of the withdrawals by wells; the reductiOIl of SCCp:lgC into many Western streams which were fornH..:rl: pcrcnnbl but tJre now ephemeral. Sometimes the full elIect of pumping is felt upon surface-water supplies only after long delay: the Pecos River Compaer,':' specifying thilt the river in New ?\.li:xic() sh;dl not he depleted hy m;lIl's ;)ctivities helo,,, "the Ig.t7 rondition," poses ;1 complex problem 01 interpretation-hoth of the Ilydrology ,llld of the Compa(t'... wnrdillg-- hCC<lllSe of the tributary Roswell ground-water reservoir. WATLR MANAGEMENT FOR OPTH\'lUJVI USE We kwe today many comprehensive programs of watcr management involving reservoir operation, but they are concerned with sllrf<1ce water. Reservoir operations have some similarity to husiness or hankinp; operations where there are drtily and s(~as.onal and annual fluctuations in income, and o.;illliJar but noncoirrcidcnt fluctuadons iJl OlltgO, and where there is some reserve to dip into in periods of peak outgo. For efficient reservoir manaR"C'- lllcnt. \'\'hether of surface water or ~round water, one should have a con- tinuing inventory of the storage in the reservoir, ;Jl1d of the inflow and oUf- flow. And he should know these factors well enough to enable him to anticip;J(c the future and to projec[ his oper:Hions accordingly. The basic data needed for efficient reservoir ll1<1nagement, therefore, arc those that permit computations of the reservoir capacity. the lls~lhle stor;tge in th~ reservoir. innow or recharge to the rbL'rvoir, :IIHI the outflow or discharg(' fTom the reservoir. These dat<1 arc required for C~llh individual reservoir. because each h:1." its Ol""'n unique complex of topography. soils, geology, :llld dim<1te. l"PCCO<; River COlllpacl. Public La\\' ~Jf. RLa Congress, Is(, Scs..;ioll. SCII;Jtc DOCII- IllClll ,'\n, 1()~1. I~l.pl: \V:I"hillgIOI1, I: s. e\l\'!. I']'illlill~~ Ollic\". ,~'\i\' pIllS Ii? p.: 1;1 Slar. 1:;~J