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<br />The MCPC utilized this data to calculate the recurrence interval for each hazard, and thus make a <br />determination of the probable frequency of future hazard events. <br /> <br />The Hazards <br />The hazards identified as having had past occurrence in the planning area are: <br /> <br />Flooding <br />Riverine flooding is defined as when a watercourse exceeds its "bank-full" capacity. Riverine <br />flooding generally occurs as a result of prolonged rainfall, or rainfall that is combined with <br />already saturated soils from previous rain events. Colorado has never experienced a serious <br />flood from snowmelt alone (CWCB Flood Mitigation Plan, 1986). Floods from rain on top of <br />snowmelt are more common. Flash flooding is defined as those floods that rise and fall within a <br />four-hour period. Flash floods are generally associated with intense rainfall events over confined <br />watersheds or with dam or levee failures. <br /> <br />When flooding occurs, water overflows into the floodplain, the area that is naturally inundated <br />by floodwaters (not those areas that are flooded as a result of watercourse blockages, such as <br />bridge constrictions or debris-clogged culverts). In its common usage, the floodplain most often <br />refers to that area that is inundated by the 100-year flood, the flood that has a 1 % chance in any <br />given year of being equaled or exceeded. <br /> <br />The 100-year flood is the national standard to which communities regulate their floodplains <br />through the National Flood Insurance Program (NFIP). Most of the floodprone counties and <br />incorporated communities within the planning area participate in the NFIP. Participation in the <br />NFIP requires adoption of a local floodplain management ordinance and its enforcement within a <br />mapped Special Flood Hazard Area. These maps are mostly produced and provided by FEMA <br /> <br />Flooding has occurred frequently within the planning area. The most significant floods were in <br />1935, 1965, 1969, 1995, 1997, and 1999. However, as the table below indicates, many other <br />floods have struck the planning area as well. <br /> <br />Flood Occurrences per County: 1950-2003 <br />Cheyenne 7 <br />Elbert 5 <br />Kit Carson 8 <br />Lincoln 4 <br />Logan 9 <br />Morgan 11 <br />Phillips 4 <br />Sedgwick 4 <br />Washington 10 <br />Weld 20 <br />Yuma 10 <br />11 County Total 92 <br /> <br />Source: National Climatic Data Center <br /> <br />Based on the information above, the northeast Colorado planning area has experienced an <br />average of 1.7 floods per year. Most of these floods were less than the 100-year flood; the chance <br /> <br />13 <br />