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