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<br /> <br />The flood profiles shown in this report are based on the effects of flow <br />through unobstructed hydraulic structures and are, thus, considered valid <br />only if these structures remain unobstructed and do not fail. <br /> <br />Elevations for small streams that run parallel to Vallecito Creek and Grimes <br />Creek were taken from the corresponding profiles for those two streams. <br /> <br />For all streams studied by approximate methods, the slope-area method was <br />employed to obtain flood elevations. <br /> <br />All elevations are referenced to the National Geodetic Vertical Datum of <br />1929 (NGVD). Elevation Reference Marks (ERMs) used in the study are shown <br />on the maps. ERMs shown on the FIRM represent those used during the <br />preparation of this and previous Flood Insurance Studies. The elevations <br />associated with each ERM were obtained and/or developed during FIS <br />production to establish vertical control for determination of flood <br />elevations and floodplain boundaries shown on the FIRM. Users should be <br />aware that these ERM elevations may have changed since the publication of <br />this FIS. To obtain up-to-date elevation information on National Geodetic <br />Survey (NGS) 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.noaa.qov. Map users should seek verification of non-NGS ERM <br />monument elevations when using these elevations for construction or <br />floodplain management purposes. <br /> <br />4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS <br /> <br /> <br />The NFIP encourages State and local governments to adopt sound floodplain <br />management programs. To assist in this endeavor, each FIS provides 100-year <br />floodplain data, which may include a combination of the following: 10-, 50-, <br />100-, and SOD-year flood elevations; delineations of the 100-year and <br />SOD-year floodplains; and 100-year floodway. This information is presented <br />on the FIRM and in many components of the FIS, including Flood Profiles, <br />Floodway Data tables and Summary of Stillwater Elevation tables. Users <br />should. reference the data presented in the FIS as well as additional <br />information that my be available at the local community map repository befor <br />making flood elevation and/or floodplain boundary determinations. <br /> <br />4.1 Flood Boundaries <br /> <br /> <br />In order to provide a national standard without regional <br />discrimination, the 100-year flood has been adopted by the Federal <br />Insurance Administration as the base flood for purposes of flood <br />plain management measures. The SOO-year flood is employed to <br />indicate additional areas of flood risk in the county. For each <br />stream studied in detail, the boundaries of the 100- and SOD-year <br />floods have been delineated using the flood elevations determined <br />at each cross section; between cross sections, the boundaries <br />were interpolated using topographic maps at scales of 1:1,200, with <br />a contour interval of 2 feet; 1:2,400, with a contour interval of 2 <br />feet; 1:4,800, with a contour interval of 20 feet (Reference 10, 11, <br />12, and 13). Areas studied by approximate methods were delineated. <br /> <br />12 <br />