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asphalt serve as a basis for selected from the UDFCD Criteria Manual. for wetlands vegetation were adjusted according to flow depth to account for the tendency of wetland vegetation to "lay-down" during storm events reducing their effective roughness. Following are descriptions of the channel and overbank lining types identified through the channel reaches and there associated "n"-values. In addition, Appendix B includes channel photos at various locations along with the respectively assigned "n" value. 3-1 provided for drainage structures. At these and hydraulic model At some locations the contour mapping provided by the locations, the floodplain the contour mapping. and not necessarily to District in the modeling. does not survey is drawn accurate to the field survey reflect the field vegetative the selection of the roughness coefficients ('n"-values). The "n"-values 3.1.2 Manning's Roughness Coefficients Field reviews completed to assess the channel conditions and areas covered by concrete or Final values were cross sections developed for input topographic mapping using Autodesk Civil Design right, looking downstream. drainage structure survey HEC-RAS software. All the project cross sections are stationed from left to The into the model were obtained from capacity. 3.1.1 Channel Cross Sections To accurately define the floodplain through Goldsmith Gulch section locations were established along each drainageway. locations similar to those used in the Federal Study (PIS). These locations were then accurately model changes in channel form, concrete box culvert capacity and Manning's Equation was used to analyze the 36 inch storm sewer pIpe slope, and also Emergency Management Agency (PEMA) supplemented with additional sections the locations of hydraulic structures. cross necessary to wide by 4 foot high concrete box culvert on of Arapahoe Lake and the 36 inch storm Tributary. The HY -8 culvert program was used to pIpe analyze the sewer Channel and the Flood Insurance Tributary, sections were first West placed channel at the cross were analyzed using the HEC-RAS Bridge and Culvert 3.2 HYDRAULIC PARAMETERS Parameters necessary for hydraulic computations in HEC-RAS consist of channel cross sections, roughness coefficients, and bridge/culvert geometry. Manning's Grass Lined with Asphalt Street Channel LOB -left overbank ROB - right overbank 0.035 0.018 0.035 study was completed using the Army Corps of Engineers HEC-RAS River Analysis System Version 3 determine the capacities of channel sections and structures through the study limits. Grass Lined with Grass Low-Flow Channel Grass Lined with Wetland Low-Flow Channel Concrete Channel 0.015 0.035 0.015 0.050 - 0.080 0.015 0.035 3.1 GENERAL The purpose of this analysis and the West Tributary including channel selection of appropriate channel Manning's roughness coefficients, cross and their hydraulic parameters, and modeling of bridge and culverts. The hydraulic analysis 1.2 to The hydraulic analysis includes the determination of for 3.1.3 Bridge/Culvert Characteristics The bridges and culverts in the study reaches routines. The only exceptions to this are the 8 foot Goldsmith Gulch immediately downstream underneath Boston Street on the West this Description Grass Lined with Concrete Low-Flow Channel 0.035 LOB 0.035 0.035 0.015 0.035 ROB 0.035 sections CHANNEL is to determine the hydraulic structure capacities. and the conditions of the channel along Goldsmith Gulch "n"-V ALUES Table 3-1 - Manning's Roughness Coefficients SECTION 3 HYDRAULIC ANALYSIS