The U.S. Department of Agriculture Forest Service has identified hazard concerns for areas downstream from five Colorado dams on Forest Service land. In 2009, the U.S. Geological Survey, in cooperation with the Forest Service, initiated a flood hydrology analysis to estimate the areal extent of potential downstream flood inundation and hazard to downstream life, property, and infrastructure if dam breach occurs. Readily available information was used for dam-breach assessments of five small Colorado reservoirs (Balman Reservoir, Crystal Lake, Manitou Park Lake, McGinnis Lake, and Million Reservoir) that are impounded by an earthen dam, and no new data were collected for hydraulic modeling. For each reservoir, two dam-breach scenarios were modeled: (1) the dam is overtopped but does not fail (break), and (2) the dam is overtopped and dam-break occurs. The dam-breach scenarios were modeled in response to the 100-year recurrence, 500-year recurrence, and the probable maximum precipitation, 24-hour duration rainstorms to predict downstream flooding. For each dam-breach and storm scenario, a flood inundation map was constructed to estimate the extent of flooding in areas of concern downstream from each dam. Simulation results of the dam-break scenarios were used to determine the hazard classification of the dam structure (high, significant, or low), which is primarily based on the potential for loss of life and property damage resulting from the predicted downstream flooding.
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USGS Numbered Series
Flood hydrology and dam-breach hydraulic analyses of five reservoirs in Colorado