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FLOOD00305
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Last modified
11/23/2009 1:21:56 PM
Creation date
10/4/2006 9:11:51 PM
Metadata
Fields
Template:
Floodplain Documents
County
Yuma
Community
Wray
Title
FIS - Wray
Date
12/19/1984
Prepared For
Wray
Prepared By
FEMA
Floodplain - Doc Type
Current FEMA Regulatory Floodplain Information
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<br />and culverts. During floods, debris collecting on bridges can <br />decrease the carrying capacity of the river and cause greater depth <br />upstream of the structures (backwater effect). As floodflows <br />increase, masseS of debris may break loose and cause a "wall" of <br />water and debris to surge downstream until another obstruction is <br />encountered. In some instances, debris may collect to the point <br />where structural capability is exceeded and the bridge is destroyed. <br />Because the occurrence and amount of debris are indeterminate <br />factors, only the physical characteristics of the structures were <br />considered in computing the water-surface profiles. Similarly, <br />maps of the flooded areas show the backwater effect of bridges and <br />culverts, but do not reflect increased water-surface elevations <br />that could be caused by debris collecting against the structures <br />or the deposition of silt in the stream channel under structures. <br /> <br />All elevations are referenced to the National Geodetic Vertical <br />Datum of 1929 (NGVD). <br /> <br />4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS <br /> <br />The NFIP encourages State and local governments to adopt sound flood <br />plain management programs. Therefore, each Flood Insurance Study produces <br />maps designed to assist communities in developing flood plain management <br />measures. <br /> <br />4.1 Flood Boundaries <br /> <br />To provide a national standard without regional discrimination, <br />the I-percent annual chance (lOO-year) flood has been adopted by <br />FEMA as the base flood for flood plain management purposes. The <br />0.2 percent annual chance (500-year) flood is employed to indicate <br />additional areas of flood risk in the community. For each stream <br />studied in detail, the 100- and 500-year flood plain boundaries <br />have been delineated using the flood elevations determined at each <br />cross section. Between croSS sections, the boundaries were inter- <br />polated using topographic maps at a scale of 1:2,400, with a contour <br />interval of 2 feet (Reference 8). <br /> <br />The 100- and 500-year flood plain boundaries are shown on the Flood <br />Boundary and Floodway Map (Exhibit 2). In cases where the 100- <br />and 500-year flood plain boundaries are close together, only the <br />100-year flood plain boundary has been shown. Small areas within <br />the flood plain boundaries may lie above the flood elevations but <br />cannot be shown due to limitations of the map scale and/or lack of <br />detailed topographic data. <br /> <br />11 <br />
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