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Roughness factors (Manning's "nUl used ln the hydraulic computations were chosen by engineering judgment and based on field observations of the stream and floodplain areas. Roughness values for the main channel ranged from 0.02 to 0.04, and overbank roughness values ranged from 0.02 to 0.07. The starting water-surface elevation was derived from hand computations for the peak flow at Pecos Street. The computation derived rating curves for pressure and weir flow at Pecos Street crossing. The culverts at Holiday Glen and Holiday Circle were inc luded in the HEC-2 model s. However, three long culvert s that have limited capacity to fully contain the lO- and lOO-year peak flows were not included. These culverts extend from the east branch of Holiday Circle to loa feet downstream of Holiday Vale; from the east branch of Holiday Terrace downstream 200 feet; and from Holiday Parkway downstream 200 feet. The culvert under Holiday Parkway is submerged due to backwater from Pecos Street for the lO- and lOO-year floods. Grange Hill Creek. South Fork Grange Hall Creek. Grange Hall Creek Tributary. Basin 4100. and Brantner Gulch Cross section data for Grange Hall Creek, South Fork Grange Hall Creek, and Grange Hall Creek Tributary were taken from aerial mapping at a scale of l:6,000, with a contour interval of 2 feet (Reference 42). The cross section information on Basin 4100 and Brantner Gulch was obtained by field measurements. Field measurements were also taken to obtain elevation data and structural geometry of all bridges and culverts. Roughness coefficients (Manning's "nUl were estimated by field inspection. Values used ranged from 0.025 to 0.040 for the channel and from 0.035 to 0.070 for the overbank. Starting water-surface elevations Gulch by normal depth analysis and the culvert at the downstream study were determined for Basin 4100 by l imi t. for Brantner inspection of The water-surface elevations for Grange Hall Creek and tributaries were computed using a step-backwater model similar to HEC-2, developed by the USACE (Reference 39). The starting water-surface elevations were provided by the UDFCD (Reference 37). Big Dry Creek (Above Interstate 25) and Tanglewood Creek Cross sections used in the backwater analyses were obtained by aerial photogrammetry (Reference 43). The below water sections of all cross sections were obtained by field measurement. All bridges, dams and culverts were field surveyed to obtain elevation data and structural geometry. Roughness factors computations for the judgment and based on (Manning's "nUl used ln the hydraulic study streams were chosen by engineering field observations of the flooding sources 31