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Roughness coefficients (Manning's "fi" values) were also used as HEC-2 input. Roughness values for Oak: Creek are shown in Table 2, Manning's "n"Values. Critical depth was the starting WSEL at a location several hundred feet downstream of the study reach. For all streams studied by detailed methods, locations of selected cross sections are shown on the Flood Profiles (Exhibit 1). For stream segments for which a floodway has been computed (see Section 4.2), selected cross-section locations are also shown on the FIRM. Profiles were determined for the 10-, 50-, 100-, and 500-year floods. Flood Profiles were drawn showing computed WSELs to a plotted accuracy of 0.5 foot for selected recurrence intervals. The Flood Profiles also show the streambed elevations and locations of bridges, cross sections, and tributaries. The hydraulic analyses for this study were based on unobstructed flow. The flood elevations shown on the profiles are thus considered valid only if hydraulic structures remain unobstructed, operate properly, and do not fail. All elevations are referenced to the North American Vertical Datum of 1988 (NA VD). All sources not restudied in this first revision have been converted from NGVD to NA VD through the use of the Vertcon computer program (Reference 35). These elevations associated with each Elevation Reference Mark (ERM) were obtained and/or developed during FIS production to establish vertical control for determination of flood elevations and floodplain boundaries shown on the FIRM. Users should be aware that these ERM elevations might have changed since the publication of this FIS. To obtain elevation information on national Geodetic Survey (NGS) ERMs, please contact the Information Services Branch of the NGS at (301) 713-3242, or visit their website at www.ngs.noaa.gov. Map users should seek verification ofnon-NGS ERM monument elevations when using these elevations for construction or floodplain management purposes. 4.0 FLOODPLAIN MANAGEMENT APPLICATIONS The NFIP encourages State and local governments to adopt sound floodplain management programs. To assist in this endeavor, each FIS provides 100-year floodplain data, which may include a combination of the following: 10-, 50-, 100-, and 500-year flood elevations; delineations of the 100-year and 500-year floodplains; and loo-year floodway. This information is presented on the FIRM and in many components of the FIS, including the Flood Profiles, the Floodway Data Table and the Summary of Discharges Table. Users should reference the data presented in the FIS as well as additional information th.at may be available at the local community map repository before making flood elevation and/or floodplain boundary determinations. 34