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 Page 18 Upper and Lower Emerald Valley Dam Failure Report <br /> January 23, 2015 <br /> <br />Table 6 – Model Overtopping Breach Parameters <br />HEC-HMS <br />Variable <br />Upper Emerald <br />Valley Dam <br />Lower Emerald Valley <br />Dam <br />Top Elevation (ft) 8111 8096 <br />Bottom Elevation <br />(ft) 8099 8082 <br />Bottom Width (ft) 12 18 <br />Left Side Slope <br />(xH:1V) 0.75 0.5 <br />Left Side Slope <br />(xH:1V) 0.75 0.5 <br />Development <br />Time (HR) 0.4 0.4 <br />Trigger Method Time Time <br />Trigger Time <br />(DDMMMYYYY <br />HH:MM) <br />12Sep2013 <br />13:05 <br />12Sep2013 <br />11:35 <br />Progression <br />Method Sine Wave Sine Wave <br /> <br />7.2.5 Model Calibration Cross Section <br />DSB collected survey data were reduced and input into Heasted Methods <br />FlowMaster software to estimate peaks flows at the surveyed cross sections. <br />Peak flow estimates were determined assuming flow occurred at either critical <br />depth or normal depth depending on the location of the cross section. For <br />large flood events and relatively long reaches of stream, flow at or near <br />critical depth is an acceptable assumption (NRCS, 2013) and appeared <br />appropriate in this study. Table 7 summarizes the estimated peak flows at <br />each indirect measurement location from the DSB survey. <br /> <br /> <br />Table 7 – Indirect Flow Estimates at Calibration Cross Sections <br />Location of Indirect Measurement <br />(Source) <br />Estimated Peak <br />Flow (cfs) <br />Keeton Reservoir Spillway Control Section 606 <br /> <br />7.2.6 Keeton Dam High Water Mark & Spillway Flow <br />A survey was made of the Keeton reservoir in an attempt to establish the <br />relative high water line to establish a correlation of peak outflows through the <br />spillway control sections. Figure 21 shows the results of that survey. The <br />configuration of the reservoir with respect to the Little Fountain Creek channel <br />makes exact determination of Keeton’s high water line difficult. The gages <br />upstream of the reservoir inlet were destroyed during the flooding. Therefore, <br />a best estimate of high water line was made, yielding a height of 2.48 feet <br />above the spillway control section, which correlates to about 606 cfs from the <br />spillway rating curve. It should be noted that the spillway is capable of passing <br />up to about 8,000 cfs.