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<br />. <br /> <br /> <br />. <br /> <br />CHAPTER 4 <br />FLOODPLAIN <br />ADMINISTRATION <br />AND <br />.ELlNEATION <br />SECTION 2.0 <br />FLOODPLAIN <br />DELINEATION <br /> <br />COLORADO STATEWIDE <br />DRAINAGE AND FLOODPLAIN MANAGEMENT CRITERIA MANUAL <br /> <br />2.5 FLOOD HAZARD ZONE DESIGNATIONS <br /> <br />Flood hazard zone designations are used to identify the level of study, severity of <br />flooding conditions, type of flooding, and other floodplain information. The flood zone <br />designations can be used by agencies to regulate their floodplain developments and <br />by insurance agents in determining flood insurance rates for properties in the NFIP <br />participating communities. <br /> <br />All new floodplains that are delineated to be shown on the Flood Insurance Rate Maps <br />(FIRM) should be designated using the latest FEMA flood insurance rate zone <br />designations. New floodplain delineations that are not prepared to be shown on the <br />FIRM maps should be designated using the following flood zone designations. <br /> <br />100-year Floodplain (FEMA Zone AE) <br /> <br />100-vear Floodplain boundaries are determined using the "detailed method" as <br />described in Section 2.6, Chapter 6. The 1 OO-year water surface elevations should be <br />shown at a selected interval for this zone. <br /> <br />Approximate 100-year Floodplain (FEMA Zone A) <br /> <br />Approximate 100-vear Floodplain boundaries are determined based on the "limited <br />method" as described in Section 2.7, Chapter 6. Since no detailed hydraulic analyses <br />are required for the limited method, the 100-year water surface elevations are not <br />shown within this zone. <br /> <br />100-year Shallow Floodplain (FEMA Zone AO or Zone Xl <br /> <br />100-vear Shallow Floodplain boundaries are determined using the "detailed method" <br />as described in Section 2.6, Chapter 6. Since it is often difficult to define the 100-year <br />water surface elevations for areas of shallow flooding, average flood depths and limits <br />(between 1 and 3 feet) should be shown instead. If the average flood depth is less than <br />1 foot, the floodplain should be designated as 1 OO-year Shallow Floodplain (1 foot <br />depth). <br /> <br />Special100-year Floodplain <br /> <br />Special 1 OO-vear Floodplain boundaries are determined using the "detailed method" as <br />described in Section 2.6, Chapter 6. The 100-yearwatersurface elevations should be <br />shown at a selected interval for this zone. The floodplain designation should clearly <br />identify the type of flooding (mudflow, alluvial fan, fire area, ice flow, etc.) <br /> <br />500-year Floodplain <br /> <br />500-vear Floodplain boundaries are determined using the "detailed method" as <br />described in Section 2.6, Chapter 6. The 500-year water surface elevations need not <br />be shown. <br /> <br />AUGUST 2002 <br /> <br />FLOODPLAIN DELINEATION <br /> <br />CH4-205 <br />