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The variety and potency of influ"nces that could lead to darn failure, coupled with the propensity for Colorado's population to settle near darns provide an inevitably tragic relationship. When all of the influencing conditions for failure are exposed to the large number of darns in Colorado, significant losses must be expected. The problem is intensified through continued population growth and settlement in potential inundation zones. Also, a threat synergy exists between the iJlfluencing variables so t.hat the whole potential threat is much larger 1:han the sum of the. separate hazard e.lements. In other words, both dam failUJ,e and flclsh flooding represent sE!rious concerns, but when they interact: the overall 1:.hreat is greatly magni-. fied, as in the Rapid City, South Dako':a disaster a fe'", years a90. While it is true that darns can fail without impacting people and property, the combina- tion of the numbers of people at risk from dam failure and the number of darns in Colorado present an extremely seriouB and continuing problem. Another aspect of the darn failure hazard has recently been recognized. Al though recorded evidence does not sh:::>w much impact from seisD1.ic events on the state's darns, the threat is reaL Relatively new analyses have shown the potential for significant seismicity across tohe state (see intensity map and its corresponding Mercalli Scale at Appendix 5). Earthquakes of enough magnitude to cause liquefaction or differen1:ial settling of sediments in an embankment and subsequent failure frequently occur in Colorado. 8 The State Engineer does evaluate the safety of dams in relation to tohe potential for earthquakes. -13--