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<br />"'a[~r,Ii~Js; a~d th~ South.a,l walersfwd wa, dil'ided 'nlo 121 ,ub_watersneds The maximum size
<br />of the suh-waler,hcd, within th" study area was al:><llll 130 a~re', and the average sub.watc"hed area
<br />w~_\ 71 ~.r~s, Peak flaws at each ,,,b.wat~,,hcd outlet point "~rc calclllatcd rorth~ :_. 5-, :0-,50_,
<br />and I OO.~ear re~urrence intcrval u,ing lh~ futurc and cxi.ting land u.e condition" The ,tudy area
<br />is ,howt\ in Drawing 1 and sub-wal~r,hcd area, are sflt"'m in Urawings: lhmugh 7,
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<br />Th~ 2-Y.Jr, 5-yeJr, lO-year. 50-year, and IOO-year rainfall dislIibutions Jl five-minute tim~
<br />iner~m.nl' are prol'ided hy Tahle< 1 through 6, The 2-hour, Zone I. unadj",ted ,1Orm event is
<br />rmvided by Table I. The J_ho"" Zone I. Wlrm evem for dramage are~s betwecn 10 square mile, Jnd
<br />20 square mile. i8provided by' Table 2. The 6-nour, Zone I. stonn evem for drainage areJS between
<br />50 ,quare mil." and 75 'q""re mile:; is provided by Table 3. The 2-hour, Zone It unadjusled sWml
<br />evenl is provided by Tahle 4, Thc 3-hour, Zotle fl, 81mm event for drainage a",a, between 10 square
<br />miles and 20 'quare milc, L's provided by Table 5, The 6-ho"" Zone 11, ,wrrn event for drainage are~,
<br />hetween 50 squarc milcs and 75 'quare miles is pwvided by Table 6_
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<br />The off-,i:e area wa, divided into 41 sub-watershed" The maximum sub.wat~rsh.d size for the
<br />Natio"al Forc;.tServioc area (a,oas thal a,. Ie,s likclylobcdevel oped)wa,about lOs~llaremiles,
<br />and the ma~imum ,ub_walc"hed si~e for rangeland areas was about 5 _quare mile" Drawing 8
<br />presents rhe off-site area bounda,y and the sub.watershed bo"n darics,
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<br />Thes. rainf~lI dimibutions were used in the Colorado Urban Hydrograph Proecdme (CUlIP) model
<br />to generate hydrographs from eaoh ,ub-watershed (UDrCD, 1996).
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<br />DESIG:\' RAINFALL
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<br />The design slorm distributions used in tne ,tudy were a, reeommended by the Urban Storm Drainage
<br />Cril~ria ,\1:mllal (L.DFCD, 1969) and the Llnuglas Cmml)' Stann Drainagc Lle,ign and Tc"hni~Jl
<br />Criteria iOc)ugla' Connty, 1986}, 11\e rainfall distribution that is used depends on the ,ile Oflh~
<br />drainage aroj bo\ng ,tudicd and thc locati<ln ofth. sub-walershcd wilhin DUllglJS COUnt>,
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<br />C. COLORADO URBAN IIYDROGRAPlI PROCEDL'RE PAR"METERS
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<br />Thc CCHP eompuler program was uscd to compute ,lorm runoffhydrographs for lhc variolls sub.
<br />walersheds, ll\e version ",cd for thc ,tudy was CUlll'n_ The sub_watershed input parameters
<br />rcquiredforCL"HPa,e: sub-waeershed idemitieation number, drainage area. length ande enlroidal
<br />le"~lh, draina\!cwav slopc, impcrvious I"'rooma~e, detention and rewntion .'lora!!-c lolScs, and
<br />,nl,lualion IOls rales, .'\ summary <1r'!hcCUHP mpUlparamee~" used f(>rlhe ,malys", are rrescmed
<br />in T~blcs 7 through I 0, Tabl~ 7 pre,ents lhe CUBP input porameeers forth. West sec!ioll of the 'lUdy
<br />,"ea, Table ~ pre,em, ehe CLHI' mpLlt paramc<er. for the S"Ulhca't section "fthc ,wdy aroa, Table
<br />9 pr.",,(, e'- _ .~l -!~:' :,,~..: ~"'~HL~L"" iur Ilw CaM .~~:'''''' of [be SHld}' area, Table 10 p,...,'el1t, tllc
<br />CUHPinpmpa,amelersfortheoff.,itearca,
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<br />,II; the ,iL. olthe walershed mereases, lh~ depth or ,ainbll <ie~rea'~s lor" given o[()nn frc~lLene',
<br />An ~re"n:duoli"r1 h;tor rr\u,lb~ "ppli<:d to IhepoiJ\t rainfall ~slimales provided by tn~ '-JO.'\'\ All",
<br />(U S, Ocp~, ot'Comm."~e, 1973) 10 leooum 1'0< Ihis depth r<:lfuotion,
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<br />MO,lof[)olLgla; Cou,,~y Ii., m lhe plai". ea.! "flllC rnmmlain" but tbc wesWrn portion <If Dm'glas
<br />Cllllmy lie, in thc (oot),ills of the Rock)' Mountains, The rainfall depth fora givcn ,Wrm frequcllCY
<br />i~ slgl\ifi"~nl1y differePol in lne foothills than it i, on the pia"", To nceoum for this difference,
<br />DOLLg[a, C"ullty "LIS di,'ided i"10 3 r~il\f"lI ~,'nc' (ZOll. I. 7.otle [I, ~"d 7.""0 111), Zone 1 repre'c,m
<br />the !lverage disuihUlion ofrainfalllhat will fall on lhe east~m portion (th~ plains. "fO",,!,:"', Cmmt)',
<br />Lonc III reprc.,ems lh~ "wrage diminution <Jfr~infall thal will occur;n lhe '-'estern foothills, Zo,,~
<br />II ro~rc"cms 11,e ",<'coge r~in:~il di<\rihLL1iOI' ;l1lli~ transition belwcen Ihe l'oothill, ~"d thc plai""
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<br />p":ci"ila:i,'n L{'r'~ ~,'u"cari,,, fN 'he '"ft~,i'e ,trc;\ ~f~ ~h("\'1\ in [\r~\\'ing ~, ..\ ,ut.\\'~I~:'S,l"d i,
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<br />l'hcweightcddl,1T1Oelslopc.,,"creadjusredusingFigure41 ofeh. RunoffChaptefofthe CSDCrv,
<br />t<x illput ",!o CUHP, Sub-w'atc,,\1cd !;"""'e(ric, were mc"""ed dir~ctly from lbe mapping pr.parcd
<br />forthis study using ^RCilnfo, Maps Were created delineating the existing and I\l(llre ;mper\'iLlusnes'
<br />perccntage within lh. _,!Ud)' ~re" and in thc otT.,ite area oo,ed on cxisting wl\ing, Ihc Douglas
<br />COULLt,' )\,.l"lcr Plan (Dougl", CUUllty, 1992). ".rial phmngrapny, l:S(iS ~uadrangl" m"p', ])S{]S
<br />COUI\!Y \-lJp;. and sit" ,'i,i1>, Flllure imp"rv,m"ne,s is the impcrviousnc~sth"t ;se~pectcd at u!eimale
<br />h"i[d_'''LT ('~.lh~ "'~le"lwrl, TI1.- fUll1r" perecm impervio",,,es< orlh,' wme"hed (study :!fcn :md off_
<br />'HCI i, relati\'eI" [nw ~ecause the ,kv~I"pm~m th"t m~y ()Cem in thi_ watershed is limilcd du" tn tl,,'
<br />I.,.'k ,}f ,,,,,,labl. ";<ler 10 ,upp"n d~ld('p",~tlt aod Pc"""'C" lar~" porti,," "rIlle otT.,ilc ""tcr,hed
<br />"o.,;;;I'v'I.,1 r,>r~" j:",d \;l"d ll1eret\lf." ,,(lli~.ly to he developeu),
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<br />The ,wdy arcn is clltird\ wi[l1in lVll" 1. bm th" off.,ile arca i, ill ZOtlC I and Lo,,~ 11. 11,~
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<br />",,,,,,tied _" b~lt'g in Z(",,, [ ,("11"r. than Wo/, of lhe ,,,h-"'''le,,hed " within Zone l A _,,~.
<br />"alc"hd I, eiJs,iti~d os he''''g m /Otle [I ;fm<lfc lhan ~O~-. <,flilc ~"b-"ar"..I1~d" v.nhLn Zone II.
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