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. . . 1998. Colorado Rood Hllzllrd Mitiglltion Pllln (409) Chapter 2 - Hazard Identification and Evaluation 2.1 People and Hazards Webster's Definitions Relationships between flood hazards and population Flood: a temporary condition ot identify patterns of risk, as shown in figure 1-1. Relationships between patterns of risk and steps taken inundation ot nonnally dry toward preparedness explain degrees of vulnerability land areas to which various Coloradans are exposed. Hazard: a source ot danger Such relationships are not new to Colorado. The MItigate: to cause to become less natural phenomena involved have occurred here long harsh or hostile, to make before people settled near them and were impacted by less severe them. Risk grows from the increasingly close associa- tion between natural phenomena and a growing popu- lation. value of property, including structures and contents, People become vulnerable to hazards when they exposed to the lOa-year flood in Colorado is estimated to be over $11 billion dollars. Cumulative flood losses choose (knowingly or unknowmgly) to live near the from the turn of the century to 1993 from the state's areas where these extreme events occur. Vulnerability most damaging floods are $3.3 billion (1995 dollars). is also related to preparedness. People who prepare for the occurrence of an extreme event are less vulner- 2.2 Types of Hazards able to it than those who do not The vulnerability of Colorado's population is rooted in a relationship be- 2.2.1 Floods tween the occurrences of extreme events, the proxim- ity of people to these occurrences, and the degree to Floods in Colorado occur on "riverine" systems con- which these people are prepared to cope with these sisting of a basin (or watershed) and a hierarchical extremes of nature. order of stream channels which convey the normal flow of water through the watershed. The area adja- Today, flood prone areas have been identified in 268 cent to the channel is the floodplain. Flooding results cities and towns and in all of the 63 counties in when the flow of water is greater than the normal Colorado. Using information supplied from local units carrying capacity of the stream channel. Rate of rise, of government, there are estimated to be approxi- magnitude (or peak discharge), duration and fre- mately 250,000 people now living in Colorado's flood- quency of floods are a function of specdic physic- plains. The Colorado Water Conservation Board graphic characteristics. Generally the rise in water (CWCB) estimates that approximately 65,000 homes surface elevation is quite rapid on small (and steep and 15,000 commercial and industrial business struc- gradient) streams and slow in large (and flat sloped) tures are located in Colorado's floodplains, The total streams. Colorado Flood Facts CountieslCitlesfTowns with Flood Prone Areas I 268 Population of 100-Year Floodplain 250,000 Homes in 100-Year Floodplain 65,000 I Commercialflndustrlal Businesses in 100-year Floodplain 15,000 . Total Value of Property in 1oo-Year Floodplain $11 Billion I Cumulative Flood Losses from Turn of Century to 1997 $ 3.3 Billion Source: CWCS Figure 2-1 . . FII.:FHMP.chaptfH'-2.pub Chapler 2 - f 112",' fO.12 All