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Starting water surface el evations for the Arkansas River were ob- tained by using the slope-area method as described in Reference 10. Starting water surface elevations for the tributaries to the Arkansas River in Canon City were obtained fran the Arkansas River profile at the confluence with each tributary. The Arkansas River is the reg- ulatory flooding source in Canon City. Flood profi 1 es were drawn showi n9 computed wa ter- surface el eva ti ons to an accuracy of 0.5 foot. for floods of the selected recurrence interval s, The fl ood profil es presented in thi s study are ba sed on the effec ts of flow through unobstructed hydraul ic structures and area, and are considered val id only if these structures do not fail and remain unobstructed. Horizontal control is based on Colorado State Plane Coordinate System South Zone 1929 U.S. Coast & Geodetic Survey Sea Level Datum. Elevation reference marks used in this study are shown on the maps. 4.0 FLOOD PLAIN MANAGEMENT The National Flood Insurance Program encourages state and local governments to adopt sound flood p 1 a i n management programs. Therefore, each Flood Insurance Study includes a flood boundary map designed to assist com- munities in developing sound flood plain management measures. 4.1 Flood Boundaries In order to provide a national standard without regional discrimina- tion, the lDO-year flood has been adopted by FEMA as the base flood for purposes of flood plain managE'ment measures. The 500-year flood is employed to indicate additional areas of flood risk in t~e com- munity. For each stream studied in detail. the boundaries for the 100- and 500-year floods have been delineated using the flood eleva- tions detennined at each cross section; between cross sE'ctions, the boundaries were interpolated using topographic maps at a scale of 1:2400, with a contour interval of 2 feet (ReferE'nce 13). In cases where the 100- and 500-year flood boundaries are close together, only the 100-year fl ood boundary ha s been shown. Flood boundaries for the 100- and 500-year floods are shown on the Flood Boundary and Floodway Map. Small areas within the flood boun- daries may 1 ie above the flood elevations, and therefore, may not be subject to flooding. Owing to limitations of the map scale, such areas are not shown. 4.2 Floodways Encroachment on flood plains, such as artificial fill, reduces the flood-carrying capacity and increases flood heights, thus increasing flood hazards in areas beyond the encroachment itsel f. One aspect of flood plain management involves balancing the economic gain fran flood plain development against the resulting increase in flood 9