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5.o0~611J\I8k_EkQQQ!~~_QU~_IQ_8_Q8tl_~B~8K Because a dam formed by flowing earth structure (ie; no compaction, no impervious zone, no spillway, etc.), there is a potential for failure also from overtopping and subsequent erosion on the is not an engineered outlet works, and no due to instability and downstream face. As an example of how things can go wrong, a lake formed behind a dam at the Whiskey creek slide could saturate the toe of the Meadow Mountain slide. This might in turn cause mud to flow into the. reservoir. The displaced water might flow over the downstream face of the dam and cause it to fail. The rapid drawdown could trigger even more movement on the Meadow Mountain slide and possibly the formation of a new dam. Failure of either of the dams described in this report could have serious consequences to the communities of Avon, Eagle, and Gypsum. Lessor impacts could be possible all the way to Grand Junction depending on the mode of failure. Recent preliminary estimates by the engineers of the Dam Safety Branch of the State Engineer indicate the. dam break discharge from the sudden failure of a 200 foot high dam at Dowds Junction would be approximately 1.2 million cubic feet per second. 5.1 ElQQg_Qgetn~ Approximate flood depths were assumed using the "Method for the Rapid Identification of Dam Failure Floodplains in Colorado" developed by the Colorado Water Conservation Board staff in 1983. This procedure has been published by the Division of Disaster Emergency Services as an appendix to the report entitled" Colorado's Vulnerability to Very High Risk Natural Hazards." The method was developed for emergency planners and does not require the more complicated and uncertain calculation of peak discharges. Instead, the depth of the flood is assumed directly based on the height of the dam. Attenuation of flood depths downstream from the dam is based on experience learned from other dam failures. The level of detail is compatable with the limited scale on the available topographic maps used to show flood boundaries. Further refinement based on calculated flood discharges would not increase the accuracy of the maps. The following table summarizes the flood depths assumed below Dowds Junction.