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- Water-surface profiles of the selected recurrence intervals on the Rio Blanco were developed using the u. S. Army Corps of Engineers - ~ep- aCKWa~c~ ~~ro ~:~J Reference 11). Starting eleva- tions were computed us~ng e ::;1.....J:"e arcJ.. 1'!:lp+nnn a - profiles of San Juan River, McCabe Creek, North Fork McCabe Cree, and West Fork McCabe Creek were developed using the u.S. Soil Conservation Service WSP2 computer program (Reference 12). The results were reviewed and adopted for this Flood Insurance Study. Flood profiles were drawn showing computed water-surface elevations to an accuracy of 0.5 foot for floods of the selected recurrence intervals (Exhibit 1). The flood profiles shown in this report are based On the effects of flow through unobstructed hydraulic struc- tures and are thus considered valid only if these structures remain unobstructed and do not fail. Approximate methods were used to study portions of the San Juan River, Rio Blanco, Mill Creek, Piedra River, Navaho River. Little Navabo River, Navaho Reservoir, Rio Chama, Devils Creek, and Stoll- steimer Creek. Because there is not any previous study in these areas, an area prone to flooding for the recurrence interval of 100 years was delineated by hydraulic calculations. All elevations are referenced to the National Geodetic Vertical Datum of 1929 (NGVD) , Elevation reference marks used in the study are shown on the maps. 4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS A prime purpose of the National Flood Insurance Program is to encourage State and local governments to adopt sound flood plain management pro- grams. Each Flood Insurance Study, therefore, includes a flood boundary map designed to assist communities in developing sound flood plain management measures. 4.1 Flood Boundaries In order to provide a national standard without regional discrimina- tion, the 100-year flood has been adopted by the Federal Insurance Administration as the base flood for purposes of flood plain manage- ment measures, The SOO-year flood is employed to indicate additional areas of flood risk in the conununity. For each stream studied in detail, the boundaries of the 100- and SOO-year floods have been delineated using the flood elevations determined at each cross sec- tion; between cross sections, the boundaries were interpolated using topographic maps at scale of 1:2400, with a contour interval of 2 feet (Reference 13). 12 .