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<br />floodplain area with ground level photography used as an aid in the <br />selection of the roughness factors and aerial photography used to <br />determine the lirni ts of each roughness zone. For the Arkansas <br />River and tributaries studied the roughness coefficient for the <br />channel was 0.03, while the value ranged from 0.025 to 0.065 for <br />the overbank areas (Reference 3) For the NE Canon Drainage Area <br />that was studied, the roughness coefficients ranged from 0.035 to <br />0.065 (Reference 2). <br /> <br />Starting water-surface elevations for the Arkansas River were <br />determined by the slope-area method. Starting water-surface <br />elevations for the tributary creeks of Oak, Coal, and Chandler <br />Creeks, and the NE Canon Drainage Area, were determined from a <br />water-surface profile calculation on the Arkansas River using a <br />coincidental flow relationship for the discharge in the Arkansas <br />River (References 1 and 2) . <br /> <br />Flood profiles were drawn showing the computed water-surface <br />elevations for floods of the selected recurrence intervals. <br /> <br />The hydraulic analyses for this FIS are based on unobstructed flow. <br />The flood elevations shown on the profiles are thus considered <br />valid only if hydraulic structures remain unobstructed, operate <br />properly, and do not fail. <br /> <br />All elevations are referenced to the National Geodetic Vertical <br />Datum of 1929 (NGVD). Descriptions of Elevation Reference Marks <br />(ERMs) are shown directly on selected FIRM panels; the remaining <br />descriptions are presented in Elevation Reference Marks <br />(Exhibi t 3). ERMs shown in Exhibit 3 represent those used during <br />the preparation of this and previous Flood Insurance Studies. The <br />elevations associated with each ERM were obtained and/or developed <br />during FIS production to establish vertical control for <br />determination of flood elevations and floodplain boundaries shown <br />on the FIRM. Users should be aware that these ERM elevations may <br />have changed since the publication of this FIS. To obtain <br />up-to-date elevation information on National Geodetic Survey (NGS) <br />ERMs shown on this map, please contact the Information Services <br />Branch of the NGS at (301) 713-3242, or visit their website at <br />www.nqS.Doaa.qov. Map users should seek verification of non-NGS <br />ERM monument elevations when using these elevations for <br />construction or floodplain management purposes. <br /> <br />4.0 FLOODPLAIN MANAGEMENT APPLICATIONS <br /> <br />The NFIP encourages State and local governments to adopt sound floodplain <br />management programs. To assist in this endeavor, each FIS provides <br />lOO-year floodplain data, which may include a combination of the <br />following: 10-, 50-, 100-, and SOO-year flood elevations; delineations <br />of the 100-year and 500-year floodplains; and 100-year f1oodway. This <br />information is presented on the FIRM and in many components of the FIS, <br />including Flood Profiles, Floodway Data tables and Summary of Stillwater <br />Elevation tables. Users should reference the data presented in the FIS <br />as well as additional information that may be available at the local <br />community map repository before making flood elevation and/or floodplain <br />boundary determinations. <br /> <br />8 <br />