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<br />1 4.0 HYDRAULIC ANALYSIS <br />' 4.1 Base Mapping <br />Base mapping selected for the delineation of the 50-year and 100-year floodplains on the White <br />River consisted of 7.5 minute U.S.G.S. topographic quadrangle maps. A total of 12 quadrangle <br />maps were used in compiling the base maps for the White River study reach. The contour <br />interval for the maps was either 20 or 40 feet (see Figure 8). Due to the small scale of the base <br />maps (1"=2000'), the 50 and 100-year flood plain boundaries could not be shown as separate in <br />most cases. <br />4.2 Stream Reaches <br />Preliminary work on the floodplain mapping of the White River included dividing the entire study <br />reach into separate stream reaches. The reaches were classified by estimating stream floodplain <br />widths. The width classifications were refined once cross-sections were plotted. The width <br />classifications selected are based on the distance from one side of the river to the other at a <br />I ground elevation 15 feet above the low water level. Those classifications are: <br />Broad - >0.5 mile wide; <br />Medium 0.2 - 0.5 mile wide; <br />Narrow - 0.1 - 0.2 mile wide; <br />Canyon - <0.1 mile wide. <br />Based on these standards, there were 10 separate stream reaches classified for a total of 52 river <br />miles. That is an average of 5.2 miles per reach. These 10 stream reaches are listed in Table <br />4 and they are shown on Figure 6. <br />1 <br /> <br /> <br /> <br /> <br /> <br /> <br />14 <br />