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3.2.1.3 Road and Path Crossings There are fourteen road crossings of Fourmile Canyon Creek within the study area. The road crossings range in size from small culverts to bridges. During floods, debris transport is common within streams in the City. To address the potential increase in flood elevations upstream of road crossings caused by debris blockage, the City requires the conveyance of road crossings with potential for debris blockage be reduced. Table 7 identifies the debris blockage for road crossings along Fourmile Canyon Creek approved by the City and the UDFCD based upon experience during flood events of how these crossings function. Blockage is modeled in bridges and culverts by lowering the low chord of the upstream cross section of the opening to reduce the opening by the percent blockage in Table 7. Table 7. Percent Blockage Within Fourmile Canyon Creek Crossings in the LOMR Crossing Percent Type Blockaee Broadway St. 0% Brid~e Violet Ave. 40% Brid~e Upland Ave. 50% Bridge 19th Street 10% Bridge Sumac Ave. 30% Bridge Topaz Drive 30% 2 x 5- x 3-ft Ellip. Culvert Folsom A ve.l 20% Bridge 26th Street Elks Club Brid~e 40% Bridge 28th Street 0% Bridge 30th Street 0% Brid~e 47th Street 100% CMP & RCB Diagonal/State 0% East & West Highway 119 Bound Bridge 5th Street 100% 42-in CMP 615t Street 100% Culvert The method used to model crossings in HEC-RAS was selected based on a thorough analysis of the data produced under different modeling methods available in HEC-RAS and engineering judgment. Most bridges were modeled using energy for low flows and pressure/weir for high flows. For low flows, Yarnell and momentum modeling methods were not used because they apply only to specific circumstances. Yamell is based on a limited empirical data and can give unreliable results. Momentum requires a uniform cross section or it can calculate unrealistic losses and result in unreliable results; along -] 6-