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the calculated 50-year frequency flood event. A 19,000 charge was recorded on the Roaring Fork River in 1957. is equivalent to the calculated 50-year frequency flood (Reference 2). cfs dis- This flood event No significant low-lying areas exist along the Colorado River, but two can be found on the Roaring Fork Riverl one is a trailer park and the other is an area near the sewage treatment plant. Numerous severe floods occurred in the areas studied by approximate methods. These floods were caused by short, intense thunderstorms and were accompanied by mud and debris flows. Long-time residents of the area report that floods occurred in the early 1930s and mid-1940s, although no newspaper accounts can be located. More recent floods occurred on July 24, 1977, and July 12, 1981. The 1977 floods took place on the afternoon and evening of July 24, following a period of prolonged drought. A brief, but very intense, thunderstorm generated debris flows and mud floods in many of the watersheds draining onto the southern two-thirds of the city. Flooding affected nearly 200 acres within the city, leaving mud and debris deposits of up to 4 feet near the fanheads and sheets of silty mud 2 to 4 inches deep between Grand and Glen Avenues and the Roaring Fork River. Initial estimates of the damage were as high as $2 millionl however, the final tallies indicated that a figure on the order of $500,000 was probably closer to the actual total. This translated to a per capita cost of between $50 and $100 (Reference 6). The July 12, 1981, flood was in many respects a smaller version of the 1977 event. Approximately $100,000 in damage resulted. As in 1977, the floods occurred after an unusually dry winter and spring. Smaller debris flows, mudflows, and waterflows followed throughout the summer, although none achieved the magnitude of the July 12 event (Reference 6). Photographs of the flooding are shown in Figures 2 through 7. Because of the well-defined channels of the rivers in the Glenwood Springs area, there are no problem flood areas, with the exception of existing houses located on the alluvial fans of the small basins around Glenwood Springs. 2.4 Flood Protection Measures The Roaring Fork and Colorado Rivers exist in deep channels. There are no authorized flood-control structures in the study areal there- fore, none are under investigation. A series of major water-supply storage reservoirs exist in the upstream areas of both basins, but these reservoirs are not specifically designed for flood control. Flood protection facilities in the areas studied by approximate methods consist of the Cemetery Gulch on the 12th Street drainageway 6