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Y .. <br /> r t <br /> s <br /> Northeast Section looking West& East <br /> Clear Day Release—Pipinp <br /> As discussed with the SEO, Civil Resources analyzed the potential release of the volume stored above the estimated <br /> natural grade due to"piping"as a worst-case scenario. The State Engineer's Office spreadsheet for breach was used to <br /> estimate the peak release due to piping. Lidar data(https:Hcoloradohazardmapping.com/lidar)was used in HEC-RAS <br /> modeling software to perform a breach analysis of the northeast corner of the reservoir. If a five-foot-deep by 47.3 feet- <br /> wide breach were to occur then a peak release of 1,101 cfs would be released northeast along an existing drainage into <br /> the reclaimed ski lake to the northeast. HEC-RAS was used to estimate the extent of flooding due to the release of the <br /> 1,101 cfs resulting in estimated flood depths just downstream of the critical section of approximately three(3)feet and <br /> one to two feet deep at the most downstream HEC-RAS section. In comparison,the South Platte River modeling <br /> estimates that the river flow is approximately 20,000 cfs at this location with flood depths of four to five feet during the <br /> 100-year flood event and that this whole area is in the floodway. <br /> Conclusion <br /> Civil Resources reviewed the potential impacts of overtopping and clear day piping failure of the subject north fill area <br /> and concluded that no loss of life would be expected during a clear day failure or overtopping failure of the fill area. Civil <br /> Resources further concluded that the risk is mitigated by the absence of a viable failure mechanism as summarized <br /> below: <br /> - Potential for Piping Failure: <br /> o The maximum gradient is 0.02 feet per foot(2-feet/100-feet)and does not represent a gradient <br /> required to cause a piping failure. <br /> o No outlet pipe is present that would create a preferred path by which piping typically occurs. <br />