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I I I I I I I I I I I I I I I I I I I along with other peak discharges. The only other parameter thaI is needed is a regional skew number that can be obtained from the USGS. For more infonnalion on HEC~FFA consult the HEC.FFA Flood Frequency Analysis User's Manual. 4.4 Hydraulic Analysis Computations of the water surface profile for the HXJ.}T flood are obtained from HEC-RAS computer modeling and normal depth calculations. An estimation of channel and bankfull parameters is designated from Manning's n values, locations of top of bank. weir. expansion. contraction, entrance loss, exit loss, and other necessary coefficients. The structural and hydraulic characteri..tics are entered. Floodplain boundaries from area maps that correlate with the water elevation for the IOO-year flood event are produced. The topographic maps that are produced for the floodplain are then superimposed on all maps. The final results are confirmed to fall within a reasonable range for the watershed and the computer model warnings are a.'\sessed and amended. Results are confinned with other literature sources and professionals with knowledge of similar areas and conditions. 4.5 IOO-Year Floodplain Map Delineation Floodplain delineations are completed for the given basin. The results obtained from the hydraulic model will be used to delineate the floodplain. The post-processing features of the HEC-GeoRAS ArcView extension is used to read the HEC-RAS results. generate a water surface TIN, and delineate the floodplain. All results are checked along with the floodplain width related to the topographic elevations. A floodplain map is created with flood contours that are derived from the water surface profiles that correspond to the work map contours. The floodplain map is compared to any previous infonnation of the floodplain area for the IDO-year flood. 20