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<br />Result<; and I)isrussion <br /> <br />Task I - I>e\'t~lop 6-hr storm input data for IIEC-fl:\.lS: <br /> <br />Input parameters for a 2-. J- and 6-hr storm were developed using criteria from the Denver <br />Urban Drainage and Flood Control District. Comparisons of hyetograph~ and cumulative <br />rainfall plots were made between the 6-hr storm and the :'\RCS Type I1A 2..f-hr storm (rainfall <br />distrihUlion originally selected for use in the Fountain Creek Watcr..hed Study). As seen in the <br />enclosed graphs. the volume and cumulative rainfall are greater for the 2..f-hr storm than the 6-hr <br />storm. Input data for both the 6-hr and 2..f+hr ",torms was then entered into an exi",ting conditions <br />HEC-H~1S model for Dry Creek (a tributary to Monument Creek and included in the Fountain <br />Creek \\'atershed Study) and simulations run for hoth rainfall events. The enclosed table of <br />result", for Dry Creek shows that the peak discharge from a 6-hr -;torm doe", not exceed the peak <br />discharge for the 2..l--hr storm at any location within the watershed. Basc:d upon the...e results and <br />conversations with Tom Browning. Colorado Water Conservation Board (eWCB) it was decided <br />not perform any further analysis or ...imulations with the 6-hr ",torm. All remaining HEC-HMS <br />modeling for the fountain Creek Watershed Study will be performed using the NRCS Type IIA <br />2..f-hr storm \I.'ith the exception of the composite Fountain Creek watershed. which will use a 72- <br />hr. elliptical storm pattern to maintain consistency with the original US ACE Fountain Creek <br />Hydrologic Water..hed Analysis (2()().t). <br /> <br />Task 2 - ()en~lop Confidence Inlenah for Select Stream R(';)ches: <br /> <br />For Cottonwood Creek and Ea",t Fork. Sand Creek. 951k confidence intcrval>.. were <br />computed for thc existing conditions. HEC-H\lS modeled. peak di~charge \'alue",. The method <br />used to L'ompute the confidence intef\:als i.. described in USGS Bulletin 178. Guidl'/ines!or <br />f)l'tnmilling Flood Flo\\' Fret/lie/ICY. SectIon VI and Appendix 9. The HEC-HMS modeling <br />rewlts for the 2+. 5-. 10-. 25-, 50~. 100- and 5(X)-year storm cvents pro\'ided the ha~c1ine data or <br />population upon which the 95<k, confidence interval", were computed. For Cottonwood Creek. <br />confidence intervals were prepared for three locations: at Woodmen Road. at Rangewood Drive <br />and at the outlet of the watershed near the contlucnce with \lonument Creek. For East Fork. <br />Sand Creek confidence intervals were also prepared for three locations: downstream of the <br />crossing with Constitution Boulevard. downstream of Power", Boulevard and at the L'Ontluence <br />with the main Slem of Sand Creek. The results of these computation.. are provided on the <br />enclo"ed graph... <br />Included with the graph for COllonwood Creek near the contluen<.:e Wilh Monument Creek. <br />are point", from the gage analysi~ for the USGS gage at the same IOC.l.lion. On thi... graph. the <br />peak di...charge \'allle" computed hy the HEC-H~1S model dl\'Cfge slightly from the gaga analysis <br />\'allles. Thi~ i~ due to lhe fact that growth i... continuing throughout the Cottonwood Creek <br />watershed and the u...e of detention facilities is not reqllired within thi.. watershed. This trend <br />appear", (0 he ..upported hy the USGS gage data ,ince for the 19 year", of records the annual <br />a\wage peak flows haw "teadily increased. <br /> <br />tll... Cr'rr"r~ll"n <br />\Ntl(l h-d<:rall>nH". SUII~ ~"I <br />c.'I"r.l,I""rnn!:,COS'~~1 <br /> <br />J '217 J 1~_~-1\R<',ulb It'>:ll n"len'" 0.1116 dOoc <br />