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~~ <br />Event fi Duration Runoff Volume (A~ Peak Inflow (cfs) <br />10-year, 24-hour 15 111 <br />100-year, 24-hour 36 262 <br />Tables 5 and 6 provide the results of analyses of the riser pipe and combined elevation-discharge <br />data for Pond G. Hydrologic routing of these flows through Pond G indicates a 100-year outflow of 82 cfs <br />with a corresponding water surface elevation of 6834.8 feet. Results for the 10-year event indicate an <br />outflow of 5 ds and maximum stage of 6831.7 feet in the Pond. <br />SPILLWAY RIPRAP IMPROVEMENTS <br />The following Tables 7 through 11 provide preliminary assessments of the rock sizes required to <br />stabilize the spillways at Ponds A, D and G. In each instance, the slope used in the evaluation was the <br />maximum slope as measured by Epp & Associates during profiles surveys of the spillways conducted in <br />• 1988. For Pond G, the peak discharge is decreased substantially due to routing through the pond. In this <br />instance, we evaluated the required riprap sizes using both the 1) routed outflow of 82 cfs and 2) using the <br />peak inflow as the outflow (ignores storage routing in the pond). My analyses indicate that rock having the <br />median diameters (D50)shown in the following table are required at these ponds. This analysis assumes <br />use of good quality, angular stone having a spec'rfic grav'dy of 2.65. As we indicated in our letter to you of <br />12 October 1988, research conducted at Colorado State University tends to indicate that rounded stone <br />needs to be about 40 percent larger than angular stone to remain stable urider similar design conditions <br />(slope, discharge, etc.). <br />• <br />8 <br />Water Engineering & Technology, Inc. <br /> <br />