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.. the the Lrrig<Jllo11 tlJ.\~ ~rr.j.lany diversion Q~~..;J if lUKOIlly ~val1ablc 3. Given the Ju~t decided upon dlver~i(ln "'lnL, th~ ....;Ilcr ;lv;tlJ;ddJlty 0[\ the CHms liervC!d the d~\dl lid c:llclIlato.=d. It \s the t!lVCO",'tOll uunt reduced by c.anLll seepage losses. This water .:IIlability (cy.prcs~i(~d by then ;JS .1 depth) On the !"HIS ls compared l,) thl.' lrrlgatillrl rl:qlJir~mL'nl Isu cxpre!ds~d as a depth) determined frum cffec- V~ precipitation. crop mix, ev~potrans?iration d fnrm irrigation effi.ciency. The ratio of depth .li\;:lb1e to de.11th requlred expresse.s the degree of Lis(actLon of irrig~tion need. If the irrigation rE".quirem~nt e:xr:eeds surface leT avaiiability 011 tIle farm, pumping [r~m thp uif~r to suppLement the surface W3ter supply is troduc:~d. rOT example, under n ~hht()ric:ai rdtcgy the knovn histoTit~l volume is pumred from ~ -'lquifer. Under an (:.8 rzeqded strategy pumping limited only by installed pumping capacity. ~. Given the just determined geep~ge losses, ~ping vo1um~s and irrigation applications on the nd, aquife.r rechdrge rates and net .....ithdraW'al tes from the ~quifer are calculated for every uarc cell of the model. 5. Given the just calculated net 'I.rithdrawal teS from. the aquifer in eve.ry cell, water- table. ~vatinn in every c.ell crossed by the riVer is lculated. Given the river flo.....s in each of these its (upstream it'.f10... i.nto the cell ptU5 return ,).... into the cell le6~ diver!l.ion {if any) in that 11) river ~tages (elevations) are calculated 0111 a stage-discharge Cllrve. Based on the differ- C~ in elevation between the ground water level and c stream surface. rQturn flo~s in each river cell c the ne~t are calculated. 6. Various computer outputs of interest ore vcd on tape or printed out for later use including: ~dicted river outflow at Julesburg and percentage ~ree of satisfaction of irrigation requirement for ;) ., . .;r~... lh~ ViJrlt1Us jt.rl~,\t~d an.!ilS. The cycle. of c.:11cu1[1- tion is rep~~ted ....e~k by week u~til th~ selected time hot"izon hus neen cuv,-'.rcd. POTc;nAL MANAGEMENT STRATEGIES ^ lflun.:.q.'.t:mclIt ~lr;ltl'KY Is vi.c'-'cJ here .:IS o'l combt.- 11<l t f on 0 f (1) p LJl1nl-'u mcasur e.s t ukcn to imp rove tt'.e system's performallce through capital expenditures (lining of canals, increas~d farm efficiency) and (2) operiltionill wat~r "lluciltion proCl!durC!5 (full respect for water rights, etc.). The measures considered for the phy~ic:al improv~ment of the system were: partiaL or cOlll!llete lining of tl\(~ c<lnals, incrcase.d 0[(- channel surL:ll:e stof<tge, improved farm-efficiency and increased !lumping capacity. Some of the considered \.later <::tilocation str':llcgles '-'ere: historic.al. alloca- tion, strict surface water-right alloc.1tlon, surLlct! ....ater-need .111ocation ;Irld pumping us needed. Numer- ous combinations arc pussible. Ultimately due to fund l~mitation~. only a fe\ol combiniltions \oIer~ tried. FiVE MANAGEMENT STRATEGIES TESTED Five runS of th~ model \oIere 111.Jdc. In the first run (Series 1 ur .!!~~ run) the :o.ystelll \01,15 thC.'. historical. system 35 it existed during the 10 years 1952-1961. The diverted and pllmped w....e.k1y volumes are th.... h1ato't"\cill ones. . The rllJ~r DQ..... ,ll Jules- burg c:llculatcd by the model '-'as found to be compar- able to historical recorded fio~s. The historical degree of satisfnction of the lrrigilt{on require- ment r~nges from 25 percent to 80 percent for the Sterlil\g No.1 ilrea and from 15 percent to ~5 per- cent for the Settlers Ditch area. In the second model run (Series 2 or Lined Ca- ~ run) canals h~ving seepage losses of 25 percen~ or more ~ere lined .....ith the result that along these canals seepage lOB6es were zero. The canals that 3 .