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• storage-discharge relationships for each pond. <br />Pond A <br />For purposes of design of riprap improvements to the Pond A spillway, the original 100-year rflow <br />hydrograph developed by Leonard Rice Consulting Water Engineers (IACWE) and shown in the ~:-built <br />plans was used in flood routing. This hydrograph was used in the original certification of the pond s~ ilway <br />and was developed for AMC III conditions. Subsequent mod'rfications to the pond in terms of ~~~ater <br />conservation storage have been previously approved based on AMC II conditions. Consequently, .'se of <br />the original 100-year hydrograph, that has a peak discharge of 763 cfs and a runoff volume of 387 acr feet, <br />is quite conservative from the standpoint of flow over the emergency spillway. <br />The 10-year flood hydrograph was developed by LRCWE to support a Technical Revision cf the <br />• <br />Sedimentation Pond A Design. This technical revision proposal was approved in January 1983. Therzfore, <br />the inflows to Pond A have not been revised for this analysis and represent approved hydrology. The <br />following are the runoff volumes and peak inflows to Pond A as developed from previous analyses cf the <br />Pond A watershed. <br />Event 8 Duration Runoff Volume (AFB Peak Inflow (cfs) <br />10-year, 24-hour 52.31 78 <br />100-year, 24-hour 387 797 <br />1 As provided in lJ3CWE letter of 23 November 1981. <br />• <br />Table-1 shows the discharges computed for the principal outlet works using the aforemer_oned <br />spreadsheet model. Spillway discharges were determined using the geometric information for the sp~'~Nays <br />shown in the as-built plans. Table 2 shows the combined stage -discharge relationship for Pc-d A. <br />Colorado Yampa Coal Company provided a spoil spring discharge of 3.8 cfs based or 1989 " <br />monitoring information. To account for this flow in the hydrologic routing, the initial water surface elevation <br />in Pond A was established at the elevation corresponding to this flowrate (6936.1 feet). This assume; that <br />steady state conditions have been reached with respect to the spoil spring discharge. Steady state <br />conditions (inflow =outflow) for an inflow of 3.8 cfs are reached when the pond water surface elev-ion <br />2 <br />Water Engineering & Technology, Inc. <br />