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• of the dewatering pipe and emergency spillway relative to <br />the embankment break-in-slope as well as the 19, 25 and 100 <br />year events total flow volumes, plotted as acre feet of <br />flow, present data in such a fashion as to enable preception <br />of how the pond will function. Assuming the pond is always <br />storing 0.148 acft of water (worst scenario?), the l0 year <br />24 hour event total flow will be contained below the base of <br />the dewatering pipe. The 25 year 24 hour event will be <br />similarly contained. The 100 year 24 hour event would fill <br />the dewatering pipe to approximately fifty percent and would <br />almost fill to the base of the emergency spillway. <br />Emergency Spillway Computations <br />The designed maximum water depth in the emergency spillway <br />is one foot. <br />Spillway sideslopes are 2 horizontal 1 vertical. <br />Spillway cross-section area: <br />One foot (water depth) x four feet (maximun channel <br />width )/2 = 2sgft <br />Spillway grade, 0.4 foot drop in ten feet = 4": grade <br />A print of the graph," Flow in triangular channel" from <br />"Handbook of Drainage and Construction Products" by Armco <br />• Drainage 8 Metal Products, Inc. is included. The 0.5 foot• <br />riprap lining of the spillway sides is considered "very <br />rough" with a "n" factor of 0.06. Referring to the "Flcw in <br />triangular channel" graph, a four percent grade, a depth of <br />flow of one foot and a "n" factor of 0.06 defines a <br />discharge rate of about 7.3 cubic feet per second at a.. <br />approximate velocity of 2.9 feet per second. The peak flow <br />for the 100 Year 24 hour event has been presented as 3.16 <br />cubic feet per second at the Yampa River Sedimentation Pond. <br />Hence the emergency spillway is more than adequate to <br />accommodate the 100 year 24 hour event. <br />If I can be of any additional assistance, don't hesitate to <br />contact me at your convenience. <br />Respectfully submitted, <br />,' <br />Eugene M. Shearer P.E. <br />~~~P p~G~57ERf~ ~-'P~\ <br />* 7Q•~n <br />`.'~ ;, <br />0 <br />s <br />i~} - ~ <br />