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Starting water-surface e~evations for the Crystal River and Castle Creek were taken at their conf~uence with the Roaring Fork River. Starting water-surface e~evations for Maroon, Snowmass, Coa~, and Hunter Creeks were determined by the critica~ depth method. The starting e~evation for the Roaring Fork River was obtained by the s~ope-area method. The starting e~evation for the Fryingpan River was taken from a ~978 F~ood P~ain Information report (Reference ~5). The hydrau~ic ana~yses for this study were based on unobstructed f~ow. The f~ood e~evations shown on the profi~es are thus con- sidered va~id on~y if hydrau~ic structures remain unobstructed, operate proper~y, and do not fai~. Hydrau~ic ana~yses of approximate-study areas were based on norma~- depth computations and information obtained from avai~ab~e topo- graphic maps and fie~d reconnaissance. An area of sha~~ow f~ooding exists a~ong the southern bank of Coa~ Creek. This area is specified as a sha~~ow f~ooding source in the F~oodp~ain Information Report for Crysta~ River and Coa~ Creek (Reference ~6). A~~ e~evations are referenced to the Nationa~ Geodetic Vertica~ Datum of ~929(NGVD). E~evation reference marks used in this study are shown on the maps; the descriptions of the marks are presented in E~evation Reference Marks (Exhibit 3). 4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS The NFIP encourages State and ~oca~ governments to adopt sound f~ood p~ain management programs. Therefore, each F~ood Insurance Study provides ~OO-year f~ood e~evations and deLineations of the ~OO- and 500-year f~ood p~ain boundaries and ~OO-year f~oodway to assist communities in deve~oping f~ood p~ain management measures. 4.~ F~ood P~ain Boundaries To provide a nationa~ standard without regiona~ discrimination, the ~ percent annua~ chance (~OO-year) f~ood has been adopted by FEMA as the base f~ood for f~ood p~ain management ,purposes. The 0.2 percent annua~ chance (500-year) f~ood is emp~oyed to indicate additiona~ areas of f~ood risk in the community. For each stream studied in detai~, the ~OO- and 500-year f~ood p~ain boundaries have been de~ineated using the f~ood e~evations determined at each cross section. Between cross sections, the boundaries were inter- po~ated using topographic maps at sca~es of ~1600 and ~1~,200, with a contour interva~ of 2 feet (Reference ~2); ~12,400, with contour interva~s of 2 feet (References ~3 and ~6) and 5 feet (References 6 and 2~); ~14,aOO, with contour intervals of 5 and 40 feet (References 14 and 22, respectively); and 1124,000, with a contour interval of 2 feet (Reference 23). 15