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conditions to interceut and carry o:t:" overland flows i.n.to adj a;;en t dra inage are~.s. Climate The climate of th,,, Westerly creek drai.ndC)e area i!3 semi.- arid and is modifie,d by thE~ Rocky Mounta,i.ns to t:he WEist. T'he average annual temperat:ure i!3 '5001'. Variations in t.emperature are ,,,ide from day to day; pcoriods of ext.remely hot weather in summer and extrem'ely co16 weather in "rinber are normally of short durat:ion and are fcllo,-^!ed by much more moderate temperatures. The average annual precipi t:a tion 1.S ::.4.:; inches, 7 5 p('rc,~nt of which occurs during the months of l\pr:i.l through Septe::nbe:c. The ~;.ummer precipitation res ul tEl fl~orn ge:.~leral1y ~\Tide.sprE~ad low pressure systems with a.s.sociat:ed low' int:en.sity rainLlll and cloudiness. Flood producing storms are generally sporadic, localized, of high intensit,y and of relativE,ly short duration. The flood season occurs .in the months of May t:hrough l\ugust:; thus, S!lOW TI\!',lt j,; not usually a contri- buting factor. Flood History From 1942 to the present, there have bee,,,, 14 years vTi.t.h flooding events on Westerly Creek of more than a !luisa.nce level during which flooding of premise,,, and impedence of traffic occured. This incidence of flooding represents an occurrence of about once every 2,,~, y'ooacs, Flooc:-causinq rainfall in th,,,se years caused overland inun- dation of homes and streets to depths of as much as 4 to 4.~; feet, particularly .in the area of the East Colfax Avenue crosEing of Westerly Creek, inte::Tupting' tra.ffic for reriod~; of up to 3 hours. East Colfax Avenue (RI:2 U.S. 40 and 287) is a ~1eavily travelled, maj or east'''WBS 'C t'loroughfare. Flood flows in this area (nort:1 of T,owry Air I'orce BaE;e) for these storm events were in the rar1CW 0:" 300 1:0 600 cfs, ",ell be- yond the capacity of existing drainage structures. In the earlier years, from 1942 t,hrough the early 1960' s, flooding problems Were confined to dLeas downstream of Lowry Air Force Base. Since about the year 1965, flood rainfall events have begun to occur in the upper'latershed as a direct result of the increasing density of development. Frequent flOOding has begun to occur in the vico:.ni.ty of thE' South Uavana Street..-East Alameda Avenue int2rS(lctio::1 u.pstream of Lowry Air Force Base. In addition, flood events in 1965 and 1973 breached and destroyed structures along the Highline 2anal, particularly in L1e area clirecL.y east of the l;est:er-. ly Creek watershed. -8-