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I I I I I I I I I I II I I I I I I I I I Hydraulic Analysis An analysis of the hydraulic characteristics of Crystal Creek and Dirty Woman Creek was performed in order to determine water surface elevations for the 100-year flood on each stream. Bridge elevations and sizes of openings were surveyed and measured in the field on March 3 and 4, 1986. This data was combined with cross-section data taken from a 5' contour mapping of the Town of Monument (Ref. 5). This cross-section data became the input data in the U.S. Army Corps of Engineers HEC-2 step-backwater computer program. The locations of the cross-sections are shown on the "Flooded Area Maps" (see Plates 2 to 5) and the hydraulic data for the cross-sections is displayed in Tables 1 and 2. Roughness coefficients (Manning's "n" values) were also used as HEC-2 input. Roughness values for Crystal Creek varied from 0.020 (concrete portion) to 0.040 for the channel and from 0.025 to 0~045 for the overbank areas. Roughness values for Dirty Woman Creek varied from 0.025 to 0.050 for the channel and from 0.025 to 0.050 for the overbank areas. The starting water surface elevations for the Crystal Creek analysis were the elevations given for Monument Lake on Monument Creek in the Flood Insurance Study for unincorporated El Paso County (Ref. 2) since this is the starting point of the Crystal Creek study. The starting water surface elevations for Dirty Woman Creek was critical depth since the first cross-section is immediately downstream from a bridge which would be overtopped during a flood. The computed 100-year fl ood is out 1 i ned on the "Flooded Area Haps", plotted on the "Flood Profile" sheets, and tabulated in the "Cross-section and Water Surface Elevation Data" tables (Tables 1 and 2). Culvert capacities are sufficient to pass the 100-year flow at all but two stream crossings. Both Beacon Light Road over Crystal Creek and the Denver Road over Dirty Woman Creek are inadequately sized. This is believed to be intentional as the backed up water temporarily floods only unused barren 1 and and the peak fl ows downstream from these roads are attenuated to a certain degree during high frequency flooding events (i. e. common fl ood events). Shoul d the 1 and upstream from either road be developed, then attention would have to be paid to the area that would be flooded and culvert size perhaps should be increased. Flooded Areas The areas covered by the lOO-year flood are shown on Plates 2 through 5. Further information with regards to flood elevations at various locations is given in the following sections of this report. Currently there are no buildings in the 100-year floodplains of either stream. An exami nat ion of the Flood Insurance Rate Map for un incorporated El Paso County (Exhibit 2) shows that flooded areas along Monument Creek do not include any lands within the present boundaries of the Town of Monument. 6