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Figure 7 —A Post -flood aerial photo of the Big Elk Meadows dams, for comparison with Figure 4 above. <br />Mirror Dam could not be seen at 7:00 pm on September 12, 2013, because of the high water flow <br />in the channel. By the morning of September 13t'the dam was gone. A failure time of <br />approximately 2:00 am was provided by first responders in the area. Figure 7 shows the after <br />failure conditions of Big Elk Meadows dams, for comparison with the before flooding image <br />provided in Figure 4. <br />0( INA0F AWM*z Kfl 29: 149XGI.I DIVA 01P1DU LTA IJ1AIk1J0V <br />10.1 Introduction <br />The Dam Safety Branch approached this investigation using standard means and methods <br />established and used by the dam safety engineering community for the study of similar events. <br />The investigation followed the "Dam Failure Investigation Guideline" by the Association of State <br />Dam Safety Officials (ASDSO) dated December 8, 2011. The U.S. Bureau of Reclamation (USER) <br />Hydraulic Investigations and Laboratory Services Group was also consulted for recommendations <br />on how to conduct field investigations and interviews. <br />A combination of methods and software were used to conduct the investigation and analysis of <br />the BEMA dam failures. The storm runoff and dam failure model was primarily developed using <br />the United States Army Corps of Engineers ( USACE) Hydrologic Engineering Center - Hydrologic <br />Modeling System (HEC -HMS) software, version 3.5. Calibration with cross section surveys to <br />estimate peak flows was facilitated by the USACE Hydrologic Engineering Center -River Analysis <br />Systems (H EC- RAS) software, version 4. 1.0 and Bentley Systems, Inc., FIowMaster software, <br />Report of the September 2013 Little Thompson River Flooding COLORADO <br />and Big Elk Meadows Dam Failures, June 2014 (Revised, Dec 2014) * Division of Water Resources <br />Page 13 of 48 b pirtm._nt or r.a,ur,r s,,sourc�, <br />DAM SAFETY BRANCH <br />