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<br />Introduction <br /> <br />FLOOD PLAIN ANALYSIS <br />EAGLE RIVER ESTATES <br />TOliN OF GYPSUM <br />EAGLE COUNTY, COLORADO <br /> <br />!Ids flood p1i1in ilnalysis was conducted to determine the flooding <br />cl1i1rilcteristics of the Eagle River at Eilgle River Estates, a new <br />subdivision in the town of Gypsum. Filing Nos. 1 through 4 of the <br />sui}division and UI,(! study area of this report are shown in Figure <br />1- <br /> <br />The results of this report are to be used to control construction <br />in the f.1oodplain. Itis the intention of the developer and of <br />the town of Gypsum to minimize the flood hilzilrcl to new residences <br />in the subdivision. <br /> <br />Method of Analysis <br />The flood plain was anillyzed using the Hec-2 water surface profiles <br />computer program developed by the U. S. Army Corps of Engineers. <br />The water surface profile was determined for the 10, 50, 100 and 500 <br />year flood events. An encroachment option was also used to deter- <br />mine the location of the floadway and of the floodway fringe of <br />the 100 year flood plain. <br />If the area of tile floodway fringel'ias filletl in to an elevation <br />above the flood water elevation so that no flow WilS permitted there, <br />the \'!ater surfilce elevation of the flood\;ay \.ould not rise more <br />than o~e foot above the normal 100 year flood wilter elevation. <br /> <br />The fol1mo/ing flows were used for the various flood events: <br /> <br />Flood Frequency <br /> <br />pischdrqe, CFS <br /> <br />. <br /> <br />10.)'(.';1:- <br />50 year <br />JOUyear <br />500Yei\r <br /> <br />5904 <br />7564 <br />8223 <br />9727 <br /> <br />PreparedOy: <br /> <br />These flm'j values were obtained frem the Hater Resources DivHion <br />oftheU. S.Geologicill Survey. The diltawilS based on flo"js recorded <br />at a gauging station ilt Gypsum from 1947 to 1978. The '.expected <br />probability" t!stir.lates were calculated using a Log Peilrson Type <br />III analysis. <br /> <br />Eldorado Engineering Company <br />823 BhkeAvenue. P.O. Box 669 <br />GlelowoodSprings, Go10rado 81601 <br />r",,"'c. r.'" .,1\- - SC;-'? 6- <br /> <br />Septel'1bf'!" 1981 <br /> <br />Cross sections of the river and flood plain were field surveyed <br />at intervals to obtain accurate representiltive topogrilphy of the <br />study area. Those cross sections l'lere input for the Hec-2 <br />p!"09fi'm. Hit> lacatioll of the sections are shown In Figure 2. The <br />existing graI.Je of each cross section is sbown in Figurc3. Elevations <br />are reliltive to lieS and Gs !lcIKhr"ilrk ilo. J-259 located (m the m, <br />pier of tile U & RGW Railroad Bridge crossing lJ. S. Highway 6 & 24 <br />in the town of CYP';lom. Benchmark eleviltion is 6319.725. <br /> <br />, <br />