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estimate of the overtopping flow is in excess of the 66 cfs inflow hydrograph predicted by <br />Sedcad. Note that this comparison assumes no routing or flow attenuation through Prospect <br />Pond, even though some routing is certain to have occurred. <br />Another method of estimating the inflow is to examine the scoured inlet to Prospect Pond and <br />apply manning's equation to dimensions determined during the September 16 inspection. <br />Again, matted vegetation, logs, and other debris were found above the scoured channel. <br />Selecting the following extremely conservative values for each dimension and parameter, this <br />method yields an estimated peak flow in excess of 400 cfs. This assumes a Manning's <br />roughness coefficient of 0.045, a trial depth of flow of 5 feet, a channel slope of 0.15 ft/ft, and a <br />trapezoidal channel with a bottom width of 2 feet with 0.5 H:V sideslopes. Under these <br />conditions, flow velocities are in excess of 18 feet per second. <br />Given these observations, it is my opinion that the Prospect Pond inflow as a result of this event <br />was probably in the 250 — 400 cfs range. This would indicate that the Sedcad model is probably <br />underestimating the resulting flood hydrograph from this unusual storm event. No further <br />conclusions for this discrepancy can be offered without additional data. <br />This hydrologic analysis of the conditions at Prospect Pond during the August 9, 2008 <br />thunderstorm event consists of the attachments listed below. I am a Licensed Professional <br />Engineer in the State of Colorado and a representative of Environmental Solutions, Inc, P. O. <br />Box 2996, Cheyenne, Wyoming. <br />cc: 21.1.2 Inspections & Reports <br />Attachments: <br />• this report (pages 1 -5) <br />• Figures 1 -5 <br />• Sedcad runs (pages 1-43) <br />3 <br />L <br />' � .•' c. pFi •, s <br />U t'' 32257 z <br />No. 32257 <br />/( /doe <br />