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 Page 16 Upper and Lower Emerald Valley Dam Failure Report January 23, 2015 7.2.3 Hydrologic Channel Routing Due to the configuration of the two Emerald Valley dams, each one downstream of the one before, no “reaches” exist between the reservoirs and routing between them was not required. Channel reaches are required and were utilized from the toe of Lower Emerald Valley Dam to the inlet of Keeton Reservoir. This routing reach was of sufficient length to warrant channel routing to accurately portray the time lag of runoff hydrographs from the subbasins, from element to element. The high-gradient mountain stream being modeled in the reach section described above are most suited for the Kinematic Wave method in HEC-HMS. A summary of the hydrologic routing parameters selected for the base model is shown in Table 5. Note that channel length, slope, and shape are fixed parameters, but Manning’s n roughness was adjusted during the calibration phase. This is not considered a sensitive parameter. Table 5 – Model Channel Routing Parameters Kinematic Wave Variable Little Fountain Creek Channel Reach Length [ft] 21734.5 Length [mi] 4.03 Slope [ft/ft] 0.076 Manning’s n 0.1 Subreaches 2 Shape Trapezoidal Bottom Width [ft] 20 Side Slope [xH:xV] 1.5 7.2.4 Overtopping Failure Breach Parameters The critical elements of an overtopping breach analysis are the breach bottom width, breach shape, and time of failure. Time of failure is also described as Breach Development time. The ultimate breach size and shape (side slopes) were measured directly during the September 25, 2013 field survey. The survey information in Figures 19 & 20 and shows the configuration of the breaches approximately 13 days after the dams breaching. To accurately model peak breach discharges, breach side slopes and bottom widths determined from that final embankment condition, immediately after the reservoir has been drained, are ideally utilized. Figure 19: UEV Post Breach Crest Profile, facing downstream