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y . . . population growth in Colorado's western counties has not been insignificant. Population densities in recreation, mining and energy producing areas are increasing rapidly. People are set tl ing near streams that rise rapidly. Al though spr ing rainfall is not normally heavy on the western Slope, concentrated rainfall from an intense storm when snowmelt run off is high, would consti- tute a significant danger. Vulnerability remains high. From an overall state perspective at least 212 towns and cities and all of Colorado's 63 counties have been associated with flood prone areas; that is approximately 150,000 people, 62,000 houses and 1,200 commercial and industrial business structures are located in Colorado's floodpla,ins. (Flood Hazard Mitigation Plan For Colorado) ~ARTHQUAKES AND POPULATION VULNERABILITY A current depiction of seismic risk to Coloradans is obtained by comparing the intensity map (map 2) on the next page to the modified Mercalli Scale on the following page. Roman numerals on the map are keyed to the scale. In other words, potential impacts described in the paragraph on earthquakes on page 5 can be expected across the State. Possibly the most dangerous of these are poten- tial dam and other structural failures that can result near population centers. The relatively high intensities found near Denver, along the Front Range and on the Western Slope seriously increase the vulnerability of people living in these areas over that expected in the recent past. DAM FAILURES AND POPULATION VULNERABILITY There is some evidence that the existence of a dam tends to develop a sense of security in potential residents. Whatever the cause, settlement has frequently occurred below Colorado's dams. People settle in the potential inundation zone that would exist should catastrophic dam failure occur, More specifically, 228 dams in the State have been categorized by the State Engineer as "high hazard," that is: if the dam were to fail then there would be significant loss of life. At a lower level of risk to people and property (essentially property damage), 337 dams within the State are classified as "moderate hazard."* Only few lives have been lost in recent years from dam failure, but property damage has been * Inundation zones for "high hazard" dams have been identified (with maps) by the State Engineer in his excellent publications which have been provided to local governments at low cost and result from the Colorado General Assembly legislation, known as "House Bill 1416." Inundation zones for moderate hazard dams can be estimated wi th sufficient accuracy for local warning and evacuation planning by use of Annex F, "A Method for the Rapid Approximation of Dam Failure Floodplains in Colorado," William P. Stanton, P.E., Department of Natural Resources, Colorado Water Conservation Board. 21