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' In performing the depth calculations, the flow on the river the day of the survey was obtained <br />from the USGS and subtracted from the established 50 and 100 -year flows for each particular <br />hydrologic point. The depth of water on the day of the survey was estimated and added to the <br />flood depth calculations to obtain the flood depths as shown in Table 6. The methodology used <br />for computing flood depths at the cross - sections is similar to the accepted methodologies used <br />by state and federal agencies in performing detailed analyses except that there is no balancing <br />of energy from one cross - section to the next. <br />' The one field- surveyed cross - section and the two map - derived cross - section are graphically <br />represented in Figures 7A - 7C. An example rating curve was prepared for the field- surveyed <br />cross - section. It is presented in Plate 16, after the floodplain maps. <br />4.5 Delineating_ Flood Boundaries <br />' The calculated flood depths for the unstudied stream reaches were first plotted on the quadrangle <br />maps at the cross - section locations. The resulting floodplain widths were compared to the <br />floodplain widths on the cross - section plots. The floodplain boundaries between the cross- <br />' sections were then approximated by delineating flood depth contours and interpreting the <br />relationship between those flood depth contours and the ground contours. Consideration was <br />given to the slope within each reach. For all of the previously studied reaches the detailed <br />delineations were transferred directly onto the base mapping without any flood depth <br />computations. The delineations for the previously unstudied reaches were blended with the <br />existing detailed delineations on the base maps. The finalized information was displayed on the <br />' USGS 7.5' quadrangle maps (scale of 1" = 2,000'). A table identifying the quadrangle maps <br />used in each plate and the map scale is given in Figure 8. The location of each floodplain map <br />plate is shown in Figure 9, and the floodplain maps are shown in Plates 1 -15. <br />F-1 <br />P <br />I <br />n <br />M <br />