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FLOOD01902
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Last modified
11/23/2009 1:09:07 PM
Creation date
10/4/2006 10:26:53 PM
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Template:
Floodplain Documents
County
Pitkin
Community
Aspen
Title
Drainage Facility Capacity Analysis of City of Aspen
Date
9/1/1998
Prepared For
Aspen
Prepared By
WRC Engineering, Inc.
Floodplain - Doc Type
Project
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<br />i . <br /> <br />e, Results <br /> <br /> <br />The output from the model is the maximum depth of flow at each node, Drawing 1 <br /> <br /> <br />shows a contour map of the maximum depth of flow through the City of Aspen <br /> <br /> <br />assuming that the water contains no sediment (C.=O,O). Drawing 2 provides the <br /> <br /> <br />maximum depth offlow assuming thatthe peak sediment concentration is 0.45, By <br /> <br /> <br />comparing the two drawings, it is apparent that sediment has a great effect on the <br /> <br /> <br />depth of flow and ultimately the design of any mitigation alternatives. <br /> <br />It is important to note that the FLO-2D model does not include the effect of <br /> <br /> <br />buildings and streets. It was modeled as if there were no obstructions to the flow, <br /> <br /> <br />Including the effect of buildings should increase the depthof flow significantly, <br /> <br />Drawings 3 and 4 provide a contour map of the water surface elevation generated <br /> <br /> <br />by the runoff from the 1 a-year, 2-hour storm with a peak sediment concentration of <br /> <br /> <br />0,0 and 0.45, respectively, <br /> <br />; <br /> <br />HEC-I was also used to provide an estimate of runoff from Spar Gulch (CUHP <br /> <br /> <br />Sub-basins 14, 22, 23, and 24) and Vallejo Gulch (CUHP Sub-basin 16), The <br /> <br /> <br />HEC-I rainfall runoff model used the Green-Ampt infiltration methodology, The <br /> <br /> <br />Green-Am pt method was used because it was assumed that since there was no snow <br /> <br /> <br />on the ground, the ground was not saturated and the initial infiltration rate would be <br /> <br /> <br />higher than the fmal infiltration rate, Hydraulic conductivity was estimated at 0,85 <br /> <br /> <br />inches per hour, This was established by varying the infiltration rate until the peak <br /> <br /> <br />flow from the basin for the 100-year storm event using HEC-I matched the peak <br /> <br /> <br />flow produced by CUHP/SWMM, <br /> <br />ii <br /> <br />The results of the HEC-I rainfall runoff analysis are provided in Tables 12 and 13 <br />for Spar Gulch and Vallejo Gulch, respectively, In comparing the results of the <br />HEC-I runoff to the CUHP/SWMM runoff, the IOO-year and 50-year flows are <br />very similar, but HEC-I ' s 2-year, 5-year, and 10-year values are much higher than <br />those produced using CUHP/SWMM (see Tables 5, 12, and 13), This primarily <br /> <br />15 <br /> <br />I <br />
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