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4.0 HYDRAULIC ANALYSIS 4.1 Base Mapping: Base mapping selected for the delineation of the 50-year and 100-year floodplains on the White River consisted of 7.5 minute U.S.G.S. topographic quadrangle maps. A total of 12 quadrangle maps were 'used in compiling the base maps for the White River study reach. The contour interval for the maps was either 20 or 40 feet (see Figure 8). Due to the small scale of the base maps (1 "=2000'), the 50 and 100-year flood plain boundaries could not be shown as separate in most cases. 4.2 Stream Reaches Preliminary work on the floodplain mapping of the White River included dividing the entire study reach into separate stream reaches. The reaches were classified by estimating stream floodplain widths. The width classifications were refined once cross-sections were plotted. The width classifications selected are based on the distance from one side of the river to the other at a ground elevation 15 feet above the low water level. Those classifications are: Broad Medium Narrow Canyon >0.5 mile wide; 0.2 - 0.5 mile wide; 0.1 - 0.2 mile wide; <0.1 mile wide. Based on these standards, there were 10 separate stream reaches classified for a total of 52 river miles. That is an average of 5.2 miles per reach. These 10 stream reaches are listed in Table 4 and they are sho\\TI on Figure 6. 14 TABLE 4 WHITE RIVER REACH CLASSIFICA nONS 11'.t~1 I 2 3 4 5 6 7 8 9 10 * 52.5-50.5 MEDIUM,20'/MI 50.5-46.5 MEDIUM, 20'/MI 46.5-45.5 CANYON, 14'00 46.5-38 NARROW, 14'/MI 37.5-24.5 MEDIUM, 13'/MI (38-37.5)* (CANYON) 24.5-19.5 NARROW, 11'00 19.5-14 MEDIUM,lI'OO 14-7 NARROW, 10'/MI 7-3 CANYON, 8'00 3-0 MEDIUM, 8'00 sub-reach in parentheses is short; it does not represent a significant enough change in stream morphology to be listed as a separate reach 15