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<br />125
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<br />of't.he district between Denver o.nd the bDBB line, wells are 80 closely
<br />". spa.ced tlio.t, when. pumped for long 'periods .the wa.ter level: declines
<br />to the pump' intake; addiliionaJ: In.rge-co.pacity wells in other parts of
<br />the district should be spaced 'farther'Rpn.rt so os to avoid mutua.l inter-
<br />ference o.nd.a subsequent loon1lowBring of the wat6l' ta.ble.
<br />There appea.rs .to be -0. danger of' overdevelopment of' the gromld-
<br />watar,supply in the South Platts E4ver,vl1lley in T. 4 N., It. 66 W.
<br />.Although the net change in wo.ter levels during the period: 1929-50 WIlS
<br />relatively smElll, a pronounced steady decline, due' pat~ly to increased
<br />. pumping and partly to subnormo1 prempiti:lrtion; hIlS- occurmd since
<br />.1950. W o.t81' levels in the a.rea immedilLtely north of :UGW~r Latb.o.m.
<br />,Reservoir do not show a marked long-term deo1ine~ probably because
<br />seepage from the reservoir is- recha.rging the ground~water reservoir.
<br />Little is known about the net change in water ,lev.els in the. rest'of the
<br />~ district between the northern boundo.ry of T. S.N. and Kuner because
<br />"long-term records' of wa.ter-level-Huctua.tions are n.ot'a.va.ilable.
<br />Although long.tel'lD.' records or water-level fluctuations in Beebe
<br />Draw are incomplete, they: indicate I.t net decline of' groWld-water
<br />levels~ at least locally. High coefficients or permeability and. tr8JJ.S~
<br />missibility of the valley-fill deposits, however, indicate that the disttict
<br />may 00' able to support additional :well-pln.n.ned grollnd-watel' denl.
<br />.opment. .An estimated 20,000 acre-ft of 'grOlwd, wdter 'WaS pumped
<br />,in 1956, apparently' without material intel'ference. lUnong wells or
<br />noticeable depletion of ground WD.ter in storage. ,If properly spaced,
<br />, additionol wells of lat'ge ,co.po.oity should not seriously deplete. the
<br />ground-water reservoir.
<br />The. maximum. development of ground water proba.bly ,hIlS 'been
<br />reached 01.' exceeded, in the:Box Elder. Creek valley, especia.lly in the
<br />stretch between Hudson and. the southern,'boundn.ry .of the repor~
<br />.area where water in' the irrigation wclls cop:unonly _ decline to the
<br />pump intake :when the weUs'lLre pumped during.extended droughts,
<br />and where. the. coefficients of 'permeability and transmissibility of the
<br />'valley-fill depomts genel'o.Uy are comparatively low. Severn.l instl\Ilces
<br />have been reported of interference among wells. Long.term records
<br />. show that ground.wo.ter levels. throughout the vuJIey hn.ve .declined
<br />sha.rply -since 1950, indicn.ting:-rather rapid depletion of the. ground
<br />water'in storn.ge. .
<br />, ' The extent to .which:development of gl"ound water in the districts
<br />. can be safely increased and,snstained depends on (1) the'u.mount.of
<br />ground..watel' available, (2)' the rate at which it is withdrawn, o.n.d
<br />.; (3) the. rate a.t which it is raplenished. . An llldication of the ammmt
<br />of groUnd wILter 11 vai1a.b1e is the uvel'D.ge, nllUl.lR1 nmount of naturn.1
<br />discharge from, It district i the. nmolmt available determines. the upper
<br />limit for development. 111' prllCtice, however, feasible development
<br />
<br />CONCLUSIONS
<br />
<br />SOUTH PLA.'ITE RIVER :BABIN
<br />
<br />tions in the report area. These deposits are the principal source of
<br />ground water in the stream valleys and, locally, they yield as much o.s
<br />2,000 gpm to we1lst 0'1tl10Ugh the Ilverage yield is a.bout 100 gpm. The
<br />low to moderate yield or some wells probably is due to poor construe.
<br />tion of the walls, and that of others to low transmissibility of the o.qui.
<br />fur. The ground wa.ter in the valley-fill deposits is unconfined, except
<br />locally, and .the depth to water rllUgea from 0 to about 80 feet:'
<br />Ground water e.nters the a.rea by underflow. The ground.wo.ter resar.
<br />voir in the area. is recha.rged also by precipitation and by seep~ge from
<br />irrigated tro.cts, reservoirs, co.nals, and streams. Ground water is
<br />discharged within the lU'ell. by evapotranspiration, seepage into
<br />streams, springs and seeps, o.nd pumping from. wells. The reinain.der
<br />of .the ground water leaves the area. by underflow tllrough the valley-
<br />fill deposits.
<br />The South Platte River gains water from the ground-"\-vater reser-
<br />voir throughout its course in the area. Beebe Seep at some times and
<br />pln.ces is a gaining stream and at others a losing stream. Water from
<br />Box Elder. Creek infiltmtes into the underlying \mCOllSolidated de..
<br />posits, especially during flood stage.
<br />Development of ground-water supplies from the va.lley-fill deposits
<br />has been rapid since 1940; the number of llU"ge.capncity wells increased
<br />from abDut 700 in 19W to about 1,700 at the end of 1957. Ground
<br />wa.ter is used principri.lly for irrigatioJl" but large amounts are used
<br />also for municipo.llJ.Ild industrial supplies. and most of the water Ior
<br />domestio and stock usa is obtained from wBlls. It is estimated ~at
<br />about 250,000 acre.ft of water in 1956 and about 100,000 acre-it in. 1957
<br />was pumped trom tIle large-cn.pllCity wells, n.nd that about 500 acre-it
<br />is pumped from domestio and stock wells annually. It is estimated
<br />that about 2 million o.ore-fi of recoverable ground water is stored in
<br />the volley-fill deposits in the report area.
<br />Further gl'Ound-watar development may be fen.sible in some pa.rts
<br />of th~ area. but. not in others. The insigni.ficant net clumge in ground-
<br />water levels between 1929 ,and 1958 in the South Platte River valley
<br />between Denvsr and the nOl.thern boundary of T. 3 N. indicates that
<br />ground.wa.ter withdrlLwals during thlLt period did not deplete the
<br />supply in storage. Even during tile period 1954-07, when preoipito.-
<br />tion 'TaS subnormal Rl1d pumpllge was correspondingly greo.ter, the
<br />net change in wnteL'lavels was very slight. Apparently, ground-water
<br />withdrawals through 1957 in this part of the aren. have r~ulted in the
<br />salvage oi watarthnt otherwise would have been discha.rged by natural
<br />processes. In plo.a8S ,,'here the water table is shallow, water now lost
<br />through evapotranspiration could be Sl.l.1vo.ged through an increase
<br />in pumping. Heavy pumping near the rivert however, might in'rluce
<br />recharge from the river l\1ld compete with surfllCB-Water use. In parts
<br />
<br />GROUND WATER,
<br />
<br />124
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