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HEC-2 n Values Cross-Sections Left Overbank Channel Right Overbank 34 - 39.5 0.045 0.045 0.045 40 - 170 0.050 0.050 0.050 180 - 190 0.045 0.045 0,045 . 200 - 255 0.040 0.040 0.040 Table 2a - Estimated n Values for Mud Gulch's Channel Cross-Sections HEC-2 n Values Cross-Sections Left Overbank Channel Right Overbank 40 - l60 0,045 0.045 0,045 170 - 240 0.040 0.040 0.040 . 250 - 700 0.045 0.045 0.045 Table 2b - Estimated n Values for Four-Mile Creek's Channel Cross-Sections The 100-year and 500-year water surface elevations for cross-sections 34 were chosen, based on a previous flood study done by Camp Dresser and McKee Inc. For some cross-section, its end points were either dog-legged and extended up-slope to close or just being left alone and allowed the HEC-2 program to extend the end points' elevations automatically. Also note that because of the wideness of the overbank areas; in an event of bank overflow, the channels would behave more like a storage than a channel flow. The 4-Mile Creek's 100-year and 500-year computed water surface elevations were used in place of the Mud Gulch's at cross-sections 40 through llO. The 100-year and 500-year water surface elevations for Mud Gulch's cross-sections 34 through 39.5 were obtained by interpolation. At some other cross-sections, as indicated in table 3, the water surface elevations were interpolated to obtain smoother flood profiles. Inserted cross-sections, at or near bridges and culverts, are not shown on the flood maps because they were used mainly for HEC-2's structural modeling. The elevations of these inserted sections were interpolated from either a upstream's or a down-stream's cross-section near the structure. At some cross-section, the channel segment was re-aligned to be perpendicular to the direction of stream flow; though this re-alignment might not be shown on the flood map. 10