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<br />Precipitation, streamflow, and paleoflood data from throughout the <br /> <br /> <br />foothill region indicate that snowmelt floods predominate above 7,500 <br /> <br /> <br />feet (2,300 meters), and that rainfall floods predominate below 7,500 feet <br /> <br /> <br />(2,300 meters) in the South Platte River basin in the Colorado Front Range, <br /> <br /> <br />Where rainfall does contribute to floods above approximately 7,500 feet <br /> <br /> <br />(2,300 meters), discharges per unit drainage area are extremely small when <br /> <br /> <br />compared with lower elevation floods resulting from rainfall, In basins <br /> <br /> <br />above 7,500 feet (2,300 meters), large floods attributed to intense <br /> <br /> <br />rainfall, which were investigated and used in rainfall-runoff-derived flood- <br /> <br /> <br />hydrology studies, were, in fact, debris flows and not waterfloods (Costa <br /> <br /> <br />and Jarrett 1981). A debris flow is a gravity-induced rapid mass movement <br /> <br /> <br />of a body of granular solids, water, and air. Debris typically constitutes <br /> <br /> <br />70 to 80 percent or more, by weight, of the flow, Use of debris flow data <br /> <br /> <br />in flood hydrology studies leads to inaccurate and extremely overestimated <br /> <br /> <br />estimates of rainfall and flood discharges. <br /> <br />EVALUATION OF STREAMFLOW RECORDS AND PALEOFLOOD DATA <br /> <br />Big Thompson River at Estes Park <br /> <br />Estes Park is at an elevation of 7,500 feet (2,300 meters), The Big <br /> <br /> <br />Thompson River has a drainage area of 137 square miles (355 square <br /> <br /> <br />kilometers), Olympus Dam, which forms Lake Estes, is located at the <br /> <br />downstream limit of Estes Park, <br /> <br />/.r <br />