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(n~3'l" e>o I .:31' b 190 Esse1&tials for Optimum Use 0/ GtOU1/d LeI' Resuurces other difficulties which must be overcome by drainage or pumping, And a few places have ideal conditions for maintaining the water table ,t the level deemed most suitable for agricultural needs, by me,ns of altemately irrigating from canals and pumping from wells, ,^,'hen olle g-ets into the swing of effIciellt reservoir operation. ground- wateT tC'ier\'oirs ;"tfC reg-arded less and Ic~s as natural accumulations of water and more and Illl)re as :lggrcgatcs of pore space which provide opportunity to store as well ;15 to withdraw wilter. Now we begin to accentu<lte the positive, :\no no lon/{cr arc subject to the limitatioll imposed by natural recharge. be- cause we can incn.'3'iC the illOow to the reservoir. Artificial rC(haT~e is proved feasible by a host of projects, I. some lItili7.ing Hood flows, somp: waste waters, ;md some operated in conjullction with Rood-control reservoirs.18 Operated in conjunction with surface reservoirs. grollnd-water reservoirs can provide the holdover storaR"c for the surplusl'.o.; of wet periods, to be withdrawn during drough t. It is anticipated that 11lanagcmellt for optimum use will involve increa.singly the importation of water from areas uf .':lurplus to areas of deficiency. Ground- water reservoirs may be sl1itable for the tcnllinal storage of SHch imported supplies, with minimum lo~s by c\'aporatioll. Undoubtedly the users of g'Tollncl-Waler reservoirs where the ;lcCllmulatt:d reserve is being depleted would be eag-er to import wateT, if the)' (ould only find all ulltapped source and justify the cost of iruporl~tion. As. poinred out by R. O. Thomas,lll Because planned utilization of lhe a\ailable underground storage ca- pacity is inherent in a progr;lIn of IIJa"iIlIlIlTl cOll...el"v;1tion nut! use. it i:; cvident that the retention of llluch of that pllrt ()f the water supply which is presently walited in outflow to the ocean <lnd in excessive evaporation by phreatophytes will require the lowering of the w;][er [able during pcrious of less-than-average supply to a much greater extent thall would otherwise occur in orner to provide rhe storagc rapacity necessary for the m<Jximum retention in the ellsuluR above-normnl period. In slI(.h a program, the ground-water reservoir would be us.cd for cyclic storilge and would be oper. ated in conjuncrion with surface T('ser\'oirs to provide a linn supply for both rhe overlying- lands within th~ natural service area of the basin and Cor the exportinK of surplus waters 10 areas of deficiency. Such 311 operarion will undoubtedly require maximum ;1rtillcial replenishment of ground w<lter and the coordinate operation of surface reservoirs so 3S to make such re- charge feasible. Thi:'i will lcrluire over-ail adminisnalive contra) by an agency empowered to exercise jurisdiction hetween. llS well as within, the geog-raphical limits of the individual hasins. 'With reference to water a\'aj)- able (or export, for example, it is actually 1I1limpOflallt whether the water js used 10 replenish .1 ]OC;]J oa:'iin and is later recovCl"cJ and delivered to an area of deficiency or whether it is rnst exported to sllch an area nnd there stored underground for later use. The net rC:'iulc. or the net COSt of rhe end product, should be approximately (he s;-rme in both cases. Any plall for operation of underground sLOf;lge which is approached from the purely local ~'iel\'poilH will provide only H:mporary relief from periodic shortages and will eventually result in the waste of orherwise recoverahle water to the detriment of areas in short supply. The ultimate in scientific management alld control of the water resources will perJwps mt:lrk rhe completion of the struggle of mall with nature, and 17D. K. Todd, ArHlOtated BibliograJlh)' on Artificial Rechnrge of Gr()1/nd IVater Through 1951, U, S, Gro!. Survey Water,SlIpply Paper 1477. 18paul Baumann, "Basin Recharge," Am. Soc. Cillil Eng. Trans., v. 122, p. 458- 501. 19R. O. Thoma.'!, "Planned Utilizarion," Am. Sue. Civil Eng. Traru., v. 122, p. 422- 442,