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<br />IlUll(iA'1 ION ANn lJllAINMiE SYSTEMS
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<br />AI'I'I.ICAN1S AND OfilECTORS ;- -~m~~j08'~
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<br />t lJenscn, ol.lIl. 1990). Wilhoul cnlibriHlon, SCS.DC Is 1I~1! 10 felle'Cj'lhti
<br />; allects of cUlling, soil evaporation after precipitation ilnd irrlglltloii'eve(I\S~,
<br />,": Bnd the effects of ClOP S\less when soil moisture is limited. The ellccls'ol .
<br />; crop stress on atfnJr" were Impolllln! In Ihis STudy as lyplr.lllly rOll'ilcis'did
<br />~ nOl irrioate alr;!lfa altr~r Ihe second CUlling. "'J~'1,t;~ll. I-
<br />d ;~~I~<it'1
<br />
<br />f
<br />
<br />l<!flns 10 c<1lculatc hisTo,ical rnor11hly ,elurn flows. The model was us
<br />delermine if ., flHm was WOller adol'\u<lte or water ShOft.
<br />;~:
<br />fQtlmliilLCllla....fnOQW!nmiHlliQl1;, Thornton used the SCS.BC~
<br />describe"in TH.21 ItJSD^,SCS, 19671. The plocNJure is a commonly use"
<br />proced\Jfe in Colorado waler transfers. At the insistence 01 NC&Wvvy.{
<br />Thornton's inCluded a component 10 lake into accourll lhe conlribu!ion
<br />crop Elp 110m non-growing season plccipit<llion
<br />":',t,
<br />NC&WWW developed a daiJy soil moislure budget modellSMB}
<br />del ermine Etp ilnd IWR. 5MB was developed usIng engineering proCCdu!a
<br />presenler! in Jensen ct. aI., 11990) and Hollman el <II. (1990}. InputflU
<br />5MB included..i!.<llIalla based relerence clap EllEtt!, basal crop coeflicler:u,
<br />drying time 01 The soil surfaCll, SCS Curve Numbers for In'illralJon_On.~
<br />runoll de I III minal ion, soil waler limits, soil mOISlure Slorage 01 non.g1011'llng
<br />season precipitllllon, inigatiOn frf!quency, lillllgc events and dales of t,he
<br />grOwing lmtl irrlgllliun ~ea~Of1~. , "",~_
<br />A 'i.
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<br />Table 2. Crop Potential Evapotrilnsplrlllion lmm) ,'c!Ii"I"'c
<br /> -, I -.,
<br /> . .1,.' . ..~'''' '.
<br /> PN82. 'PN;'I(i:
<br />C.op Month SCS Be BC.Etr PNll2 SCS.BC ",.,,-. N~:.
<br />-BC:Elr i'C;.i'
<br /> ."
<br />AlfaHa M.y 99.1 161.5 153.7 501.6 7-,5-;"
<br />. .8."
<br /> June 156.7 160.5 155.4 .1.3 .5.1,1,:
<br /> July 206.0 1701 5 170.7 .35.3 3'i'"
<br /> . . ..,' ~
<br /> Aug. 175.5 133.1 127.5 .<10.0 -5.6 '.
<br />Com M.y 77.2 26.01 25,<1 .!H,D .1.0
<br /> June 16<1.3 53.3 51.3 -113.0 .2.0
<br /> July 208.5 160.3 154.7 .53.11 -5.6
<br /> Aug. 172.2 161.5 15<1.9 -17.3 -6.6
<br /> c'c
<br />lu!gD1l~~ulr.f:.ment; Using SCS Tn21, Thornton calculated
<br />IWR as monthly con sump live use min'us eflective precipitallon. II, 'Iholr
<br />analysis, Thornton eSlimaled lha nOl depth of applicallon 10 76.2 111m 13
<br />In.1 for alllrrlgatlons. The fWR calCulated using TR21 procerlwes is shown
<br />In the third column 01 Tahle 3.
<br />
<br />Elr wa~ tlntorminod 1"ln\l n r:alihrnlnd tl;,lly [)lnnny.Crlddlo ItP/100I
<br />lIlurt'OlJ IlIe [Irl. Be [II WI1~ tJmltrJopud lIslnU tlm 1802 KlmborJy Ponmen
<br />I'll'\u<lllon (PN821 lIn<1 13 vents or ml'leorolO!Jlc,,1 dlllil from a USO~~
<br />Ao,lcultlJfal Hesea'CIl So, vice slllllon near Gleeley. Colorado, i itT~~
<br />callbriltion enlailed linear leOression analysis. wilh lhe Intercept lorced
<br />through le,o, of d~i1y values 0ltpl100 10 dilily Elf using PN82. PNB3\.IS
<br />one of lhe mOSl accufilte eCju1lIions 10' eSlimaling Iysimcter Ell In an al~
<br />climale !TobIe 7.18, Jensr.n, 19901. The 811alysi'i plovided the mont~l
<br />relalionships shown in Table 1 between tpllOO ant.! [Ir. 'ldTxr
<br />.,
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<br />T^BlE 1. MOlilhly Relalionship of 1962 Kimberly Penman's Elr IPN-;\
<br />82110 Blaney Crlddle TI>1100 :~,
<br />MOfllh Jail. fcb. Mllr. Apr. M,y
<br />PNB2 I (tpf1 00) 0.60 0.73 1.02 1.22 1.17
<br />Monlh July Aug. Sepl OCt. Nov.
<br />PN82 I (tIlIlOO) 1.12 1.06 0.94 0,87 0.75
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<br />Using 5MB NC&WWW, vilricd lha calculation nl IVl/R depending
<br />upon llle crop and farmer's Wille, supply. Till} Irrigalion heCjuency lor
<br />onions was evely five days. Corn, beets and beans on 'arms wiTh ,wells
<br />were typically II/igaled on a lilted inTerval of ooce n week. On farms
<br />. without wells these rows c'ops were Irrlgaled less ohen and the Irrigalion
<br />IreQuency was eSlimated using management allowed deficil IMADI values
<br />l . . .
<br />gIven In Table 2.7. Jensen. r.1.nII1990l. Similarly. smllll !]ralns and paslufe
<br />. Drass were I"igaled using It MAD of 60%. A!lalla was irriDallldonce at'the
<br />. .
<br />'start 01 tho season then once aoaian afler lirst And second crop. IWA as
<br />I deTermined using TR.21 and 5MB and a compallson of Iho lesulu 81l!
<br />prosented In Table 3
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<br />MonthJy eSlimales 01 EIIl oJ lhe lhree melhods were compmcd, (slle
<br />Tallie 21. Thr. monthly values 01 PNB2 and Be.Elr were determined b
<br />summing daily values from an accounting worksheel which multiplied dalf'
<br />Elf by basal clap coefficients and accounted for 5011 evapolation losse
<br />from Irligalion ..nd prccipltalion events using procedures described"ln>
<br />Jenson, 11101. (1990) and Hollman. el.ot. 119901. In TobIe 2, I3c.Etr~i
<br />compflrOS rllvorlllJly wllh PN82. WhUfUlIS Scs.nc show~ wlda vnrlnncosM("
<br />severol reasons. sCS.nc Is nOl sile speCific unless il is locally calibraled
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<br />Dllferencos In Iwn WCle direClly OllllbulOblo mall1ly 10 111 dltforonco
<br />In EI[1, (21 Tn21's mOlhod fo' celculllllng ef/ocllvo preclphnllon, lInd (3) /I
<br />dolly son moisture budgel anolysis VCISUS monthly TR21. TI121 llppe8l~ 10
<br />over.eslimato lWI1 and Etf) on 'ow crops in the eMly [1iHl 01 Ihe season
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