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<br /> <br /> <br /> <br /> <br />Northeast Section looking West & East <br /> <br /> <br />Clear Day Release – Piping <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://coloradohazardmapping.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 /> <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 /> <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.