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CARRIAGE HILLS NO. 2 DAM, Dam Failure Forensic Investigation Report Page 40 February 27, 2015 damage at the Bonza house appears to be consistent with the DSB’s definition of Low Hazard, i.e., less than 2 feet flood depth and a depth x velocity product less than seven. Low Hazard classification is not meant to trivialize the injury to an individual property owner. Due to the dam breach hydrograph’s short duration, the floodwave would have rapidly attenuated. It also would have been fully contained within Lake Estes due to its small volume. The Carriage Hills No. 2 Dam breach floodwave most likely did not affect the operation of Lake Estes. The floodwave volume of 10 acre‐feet is negligible compared to both the peak Lake Estes storage volume (over 2800 acre‐feet) and to the event’s total rainfall volume of 10,560 acre‐feet on the Fish Creek basin. Even a conservative estimate of runoff conversion shows the volume of the dam failure was minor in the scope of the overall flooding. We do not believe the dam breach floodwave made any significant contribution to channel erosion, road damage, utility damage or other widespread devastation along Fish Creek. Likewise we do not believe the breach floodwave caused the massive inflow of debris to Lake Estes: the debris along with the Big Thompson River and Lake Estes hydrographs, and the eyewitness account of upstream flooding point to a large natural flood peak along with large amounts of debris on Fish Creek after midnight on Sept. 13, 2013. It was noted that the Carriage Hills No. 1 (upper) Dam also overtopped by flood flows and experienced erosion damage. It also suffered from most of the same maintenance deficiencies as the No. 2 Dam. If the upper dam had failed it likely would have caused a cascading failure of the lower dam. A 1991 DSB breach study estimated a peak breach flow of 1162 cfs from a piping failure of the lower dam only, but a peak of 5409 cfs from a cascading failure of both dams. The latter floodwave would likely have caused significant additional damage on top of the natural flooding along Fish Creek. Finally the Carriage Hills No. 2 Dam should not be rebuilt without thorough engineering design and analysis. The hazard potential associated with failure of both the No. 1 & 2 Dams, including a cascading failure scenario, needs to be carefully studied. Both dams would need to meet safe design standards appropriate for their hazard classification, in accordance with the State of Colorado’s Rules and Regulations for Dam Safety and Dam Construction. Safe standards would include hydrologically adequate spillways, proper abandonment of old outlet works, level dams crests, and appropriate emergency action planning.