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<br />Alternative flash flood d~tectlon gY5te""~ <lte fonwlat<ld for the
<br />~ountain portion of the CAche la Poudre River ba<ln.
<br />
<br />rh~ Cache la Poodr~ River basin ha< n continental type cli~te
<br />marked by "'ide range. of Ull".perature and inegular precipitation.
<br />T'eslerty "'lnds dorntMte th~ CHrni,te for 'llO~t of the year; thLq allows
<br />the Rocky Mo~nt~1ns to btock nt~~pheric ~oi.ture originating from the
<br />?ac1fic Ocean_ During the spring and early summer months, these
<br />westerly "'inds lose their predominance and ~oist air masses push up
<br />fron the Gulf of Xexico. The plains portion of the study area receives
<br />aboot 75 percent of its precipitation during April to September_
<br />
<br />DESCRIPTION OF THE STUDY AREA
<br />
<br />GEOGRM'EiY
<br />The Cache 13 poudr~ River basin is tocated 1n north-centr"t
<br />Colorado. A major left-bank tributary of the South Platte Rlver, the
<br />Cache la Poudre River orig1""te~ withi" Rocky Mountain N..tional Pa~k.
<br />It d~ain" an area of 1,890 !O<!u..r~ "ite., and flO'o'~ about 121 m11M fro"
<br />its o~igin to it. conflucnce IO'ith the South Platte River ~bc>ut 5 miles
<br />cast of Greeley. Except for a small are"- in ~'yo",ing, almost sll of the
<br />bui:'! area i. in Larlmer and Weld Gountt"s in Colorado. Th.. basin i~
<br />shown on plate 1.
<br />
<br />The mountatnou~ reginn of the ba.in has a rigorous climate wUh
<br />long winters, heavy snowfall, and a short growing .~aso~. For example,
<br />average annu,~l ..nowhll "-t Este8 Park 15 about 96 tnche. o_omr"-red to> 43
<br />inches at Fort Collins. Tempetaturee are mo~e moderate in the foot-
<br />hilt. than in either the lllO"ntains or the plains, Climatic characteris-
<br />tics of the ?lains are low humidity, ~arm summer9, cold "'inte~., light
<br />rainfall, and considerable year to year vari~tions in pracipltation.
<br />
<br />The "''''~~e~n portion of the ~asin lies ...!thin the southern Roeky
<br />Mountain Provlnce of the Rocky Mount~ln system. Preca~brian age cock.
<br />Were uplifted and Q~posed throughout th~_ Roc;';les. The east.,rn part of
<br />thchasinlies ",tthinti,e Gr"..tPlains Provtnceof th",InteriorPlains.
<br />Und~riyiag the pl~ln~ are sedt~e"tHry s~ndstQnes. shal~a, ~nd 1i~st~~e
<br />0' c~~taceuos to tertiary a?,,,,_ Outing recent g~olog1o time, str~a~
<br />o~os1~n, gl.~C'dlt1(j11, scope ,",4~="t, ..nJ wlLlJ dellu<< ~r()Juc~J flood
<br />~Llfn., t",rraces, "nd the o'/erlying ,"lintle.
<br />
<br />Climatic data for Gteeley in the pl~ins, ~~rt Collin' in the foot-
<br />hill., and F.stes Park ln the mountains are presented in table 1. Eleva-
<br />tions for the three lQcati<>ns are 4$4$, 5025, and 7525 feet ",_s.l" re-
<br />spectivel)'. Pr"ei~it"'tlon b the ::rJu"tains e"n be ,n =ch ,~s 30 iroches
<br />a year,
<br />
<br />;jost of th", has I" "'e"t of Fort ~ollins is mounalnous. The draln-
<br />"3e ar~~ at th€ poin~ ...here the Cache la Foudre Riv~r e~ergcs fro~ the
<br />:nount.dn" is 1,055 S~U"T~ rA1le~. Th15 ar~a 1. ,'ert "~f(g"d. fe1l.~uring
<br />Hcep ~trea", slope< and "dHOW valhys. Slev"t1ol\~ 1<\ t~" "'''''l\~"b."
<br />r..n&" from ~ho"t 60.00 fe..t to ~a hi;!h a" 13,500 f"'et 'I,"ao ~ca lev,'l
<br />(",~. 1.) Local relief O[t"" ranges fr'"", 500 to 1,500 feet. The ~l"ins
<br />east vf ~l1e "",U:'ltal n~ .He c_haracter lled hy roli lng ~ill" inter"~ero"d
<br />~tth ~~~""ql"e "r~..g ,,[ g<'lltiy ~lo~".r i'hln~. ~:ev",~t"n, III the ?l:dn<;
<br />r<loge fr"," a'x>ut 6000 i~H OI.S.1. ...~ the foothills t" a>0'ut ~6QQ t,,~t
<br />,,_".1. '..11ere t1':e Ca~he la P,'udu "I~"r jQI," tl:" 3o'lt!, ?l"tle ;(lv~r.
<br />
<br />Most of the mo~ntainou$ portion of the ~atn i$ foreated ~nd the
<br />greate8t part of it is included within the RQosevelt Natlonal ,orest.
<br />Furest occur~ be~"'e~n ~lev"tion~ of 6000 to 7000 ;eet "'.$.1. op to
<br />about 11,000 feH o1,S.t. Ponderos& ~1ne or lodgepole pine, Oouglas
<br />
<br />ffr, ",",j 'i.u~k~ng ~"~cr. ,,:c fc""d c: :~c :'o.'~r elc1..~tiQ'lc. Sp~u~c~f1r
<br />
<br />forests are found at the hIgher ~levatfons. Al~in~ ~rasses and brush
<br />~nd ~arren or .naw-cavered ~re"" occur "bove the ~i"berll"c. ~O"t of
<br />th" basin 's rang~land8 and ,,It:lo..t all of the arable iands lie tn the
<br />plains, "1I.ng~ ,,"d dry cropland cypify the ::ortllern i>3rt "r th~ I't.,(~~.
<br />whll~ Irrigated nopl~"d "ccupi~" "h~ "'_l\ltherLl p..rt.
<br />
<br />3
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