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FLOOD COSTS IN 1977 DUE TO A HYPOTHETICAL FLOOD The Storm. The existence of canyons onthe tributary streams of the South Platte river renders Denver susceptible to flash floods. From these canyons and occasional torential rains, a number of suburbs have experienced floods in the past. Losses have been low because the casual storms were not extensive and population density at the time of those floods was relatively low. But conditions for broadscale as well as flash flood have always threatened Denver. Meteorlogists consider that a storm similar to that of 1965 impacting both Denver and newly populated canyons west of Denver, could occur. This opinion would have been merely speculative but for occurrence of floods over similarly situated areas. The storms of Rapid City in 1972 and over the Big Thompson in August, 1976, give considerable credence to the view that similar storms could occur anywhere along the Front Range and extend broadly enough to cover Denver. (See isohyets for storms of the Rapid City and Big Thompson flood, in the appendix to this study). There is a reasonable possibility that such a storm could occur in any given spring or summer. A storm over the Front Range west of Denver large enough to cover the metro area would release enough so that sudden impact on highly developed and valuable land would result. Such a storm is assumed to occur in 1977 in this study with the reserva- tion that this occurrence follows a winter of normal snowfall. with the soil in the mountains saturated from the runoff 'of this snow pack, stream flow would be quick and unabated. Snow pack runoff and spring rains in conjunction lead to flooding, particularly when precipitation is con- centrated and enduring, as in'the storm of 1965. In the foothills and close to Denver, the runoff could also be assumed to be faster following such rains. -18-