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I I I I I I I I I I I I I I I I I I I. Supplementary Report Page Four should be obtained from the mappers. IV. FLOOD PROFILE CALCULATIONS Because of the urban environment of each of these major drainage- ways, the flood profile, for the most part, is controlled by the street crossinas. Recoanizing this fact, each street crossing was field checked relative to pipe size and type and depth from invert to top of road. With this information, a street rating curve was developed. With this rating curve, the approximate depth of flow over the street, or at the street embankment, could be determined with the flow magnitude known. These curves were the basis for determining the flood profile at each crossing location. Channel flow depths were computed by approximating the existing channel section and computina the normal depth in the section with an average channel slope at the section location. Through- out the full reach of both quIches, a Manning's rouqhness value of .030 was used. By plotting the computed flow depths at each of the section locations on the profile drawing, the re- sulting storm water surface profile was drawn for the total channel reach. In certain areas, the flood plain can be expected to include areas above that defined by the flood profile. This peculiarity will occur near street crossinas and flat overbank areas, where the topography and street profiles are incompatible with the flood plain, and thus flood flows are diverted from the drainageway valley cross section. As a result, other areas are subjected to shallow flooding independently of the computed flood profile. These areas are included within the flood hazard area shown on the maps. Below Sixth ~venue and Federal on Weir Gulch, the area is not delineated within the hazard area but noted that shallow flooding will occur. V. SUMMlIRY To summarize, flood flows generated by a 100-year frequency storm were computed for the Sanderson and Weir Gulch Basins for a condition of total development within the basi~ry. These flows were then routed through the existing channel f~eilities to determine the approximate limits of the inundated or flood hazard area. The resulting water surface profile and approximate flooded area are presented on the plan and profile maps. Channel and street cross section information is presented on the cross section sheets. Flood flows are presented in the form of dis- charge probabili 0~:~_~~t~,s:" for each channel reach. 1~:"":..~:,"~io"Q & Gingery, Inc. !/ . _ lVJJ ::\J,"n \\ \~, -, ..J/lt \\.. .,...... -.~/-)".1 \;,' ... :.::.,-;- ',,<. /...~~,~~F.,;:.;~. :.-,'./