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<br />increased flood depths, were estimated by examining the effects of similar hydraulic <br />structures on similar streams and extrapolating those effects to Elk Creek. This approximate <br />methodology was used for the upstream reach of Elk Creek, St. Louis Creek, and the <br />downstream reach of the Fraser River (Reference 12). <br /> <br />The hydraulic analyses for this study were based on unobstructed flow. The BFEs shown <br />on the profiles are thus considered valid only if hydraulic structures remain unobstructed, <br />operate properly, and do not fail. <br /> <br />Approximate flooding along Jim Creek was determined from normal-depth calculations. <br /> <br />The hydraulic analysis for the approximate study along the Fraser River and Tenmile Creek <br />in the vicinity of Granby was conduced by using the USACE's HEC-2 step-backwater <br />computer program (Reference 6). <br /> <br />3.3 Vertical Datum <br /> <br />All FIS reports and FIRMs are referenced to a specific vertical datum. The vertical datum <br />provides a starting point against which flood, ground, and structure elevations can be <br />referenced and compared. Until recently, the standard vertical datum in use for newly <br />created or revised FIS reports and FIRMS was the National Geodetic Vertical Datum of 1929 <br />(NGVD29). With the finalization of the North American Vertical Datum of 1988 <br />(NA VD88), many FIS reports and FIRMS are being prepared using NA VD88 as the <br />referenced vertical datum. <br /> <br />All elevations are referenced to the NA VD88. To obtain up-to-date elevation information on <br />National Geodetic Survey (NGS) ERMs shown on this map, please contact the Information <br />Services Branch of the NGS at (301) 713-3242, or visit their website at www.ngs.noaa.gov. <br />Map users should seek verification of non-NGS ERM monument elevations when using <br />these elevations for construction or floodplain management purposes. It is important to note <br />that adjacent communities may be referenced to NGVD29. This may result in differences in <br />BFEs across the corporate limits between the communities. <br /> <br />For more information on NA VD88, see the FEMA publication entitled Converting the <br />National Flood Insurance Program to the North American Vertical Datum of 1988 <br />(FEMA, June 1992), or contact the Vertical Network Branch, NOS, Coast and Geodetic <br />Survey, National Oceanic and Atmospheric Administration, Rockville, Maryland 20910. <br /> <br />Temporary vertical monuments are often established during the preparation of a flood hazard <br />analysis for the purpose of establishing local vertical control. Although these monuments are <br />not shown on the FIRM, they may be found in the Technical Support Data Notebook <br />associated with the FIS report and FIRM for this community. Interested individuals may <br />contact FEMA to access these data. <br /> <br />4.0 FLOODPLAIN MANAGEMENT APPLICATIONS <br /> <br />The NFIP encourages State and local governments to adopt sound floodplain management programs. <br />To assist in this endeavor, each FIS provides 100-year floodplain data, which may include a <br />combination of the following: 10-, SO-, 100-, and SOO-year flood elevations; delineations of the <br />100-year and SOO-year floodplains; and 100-year floodway. This information is presented on the <br />FIRM and in many components of the FIS, including Flood Profiles, Floodway Data tables and <br />Summary of Stillwater Elevation tables. Users should reference the data presented in the FIS as well <br />as additional information that may be available at the local community map repository before making <br />flood elevation and/or floodplain boundary determinations. <br /> <br />11 <br />