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'" -- external help. Also, the terrain is such that Limon radar may not be able to pinpoint rain cells over the foothills such as the one which caused the Big Thompson flood, In general, the Limon radar can locate massive storm systems, but specific areas of precipitation are hard to identify. Checks are needed in individual valleys through spotter networks to determine amounts of precipitation that could be dangerous. As Colorado's populat ion grows, it is 1 ikely that most of the areas described in Table 7 and many others in the State will be under pressure for further development, thus increasing the population at risk. . '- Tourists represent another element of the population at risk in Colorado's flood areas. During the spring and summer periods, when flash floods are likely to occur, the population densities in these areas are significantly increased by tourists. Tourists represent a particular danger, in that they are unfamil iar wi th the area and the propensity for flash flooding that may exist. They probably will not be familiar with warnings or escape routes, and may be less likely to respond effectively than permanent resi- dents, Particular efforts must be made to warn tourists with roadside signs and instructions on what to do should flash floods occur, Preparedness to reduce vulnerability in these areas in particular has developed considerably in the last two years and response means have been significantly improved with better weather warning systems, see map 3, depicting NOAA* weather warning coverage around the State. But the overall vu1nerabil i ty of canyon res idents remains high because of the relatively short time of onset for most flash floods. . RIVERINE FLOODS, AND POPULATION VULNERABILITY Significant elements of Colorado's population, par- ticularly those that live along the Front Range and many of Colorado's Western Slope streams, are vulnerable to broad- scale, riverine flooding. By and large, east of the Front Range, gradients are not steep, therefore time of onset of this type of flooding is slower than with flash floods. People who live here are more susceptible to property damage than loss of life, but property damage is likely to be very high. The flood of 1965 caused damages of over 500 million (in 1965) dollars. See Annex "C" for a list of the 14 most damag ing floods in Colorado's recorded history, (from: The Flood Hazard Mitigation Plan for Colorado,) Shoula--a similar storm occur again, damages would probably be much higher (not considering inflation) since more development has occurred and water run off rates are greater, As more people move into the Denver Metro area, damages and vulner- ability must be expected to continue to increase despite effective planning now underway. . -- *National Oceanic and Atmospheric Administration 20