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22 <br />Based on available data, Sunset Lake Dam had a <br />maximum height of 6 feet with a maximum storage <br />capacity of 19.3 acre-feet. Rainbow Lake Dam, Willow <br />Lake Dam, and Mirror Lake Dam each had a maximum <br />height of 10 feet with maximum storage capacities of <br />49.0, 59.6, and 29.9 acre-feet, respectively. Meadow <br />Lake Dam had a maximum height of 10.1 feet with a <br />maximum storage capacity of 90.4 acre-feet. In 2012, <br />the Meadow Lake Dam outlet works was replaced. <br />A hydrologic study completed for Meadow Lake Dam <br />indicated the spillway was adequate to pass the Inflow <br />Design Flood (IDF) for a minor0F <br />1, low hazard dam (50- <br />year event). A spillway adequacy study was not <br />completed for the other Big Elk Meadows dams; <br />however, documents pertaining to the dams indicate <br />they all had spillway structures that were likely sized to <br />pass the 25-year storm event. The general condition of <br />the dams was thought to be good, Photos 5 and 6 <br />show Sunset Lake Dam after the failure. <br />Photo 5: Sunset Lake Dam post-failure looking across <br />and downstream from left abutment. <br />Hydrologic modeling was performed as part of the <br />failure investigation to estimate peak runoff produced <br />by the rainfall. The analyses showed Sunset Lake Dam <br />failed before its rainfall-induced peak discharge. <br />Willow Lake Dam and Rainbow Lake Dam failed <br />approximately 2.5 to 3 hours after their rainfall- <br />induced peak discharges, followed by Meadow Lake <br />Dam, which failed about 4 hours after its peak <br />discharge. Mirror Lake Dam failed about 16 hours after <br />1 Jurisdictional size dam that does not exceed 20 feet in <br />jurisdictional height and/or 100 acre-feet in capacity (CO <br />2007) <br />its peak discharge. The significant volume of inflow in <br />conjunction with the small volume of Sunset Lake likely <br />contributed to the failure of Sunset Lake Dam prior to <br />occurrence of the peak discharge <br />Photo 6: Downstream slope of Sunset Lake Dam after <br />overtopping looking from left abutment. <br />The cause of failure for these dams was overtopping, <br />erosion, and formation of a breach. Both Willow Lake <br />Dam and Meadow Lake Dam failed as a result of <br />concentrated flows at low areas in the dam crests near <br />the left abutments. Photos 5 through 10 show each <br />dam after failure. <br />Photo 7: Rainbow Lake Dam post-failure looking <br />across from left abutment.