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<br />Another HEC-RAS model was developed to represent the spill area between Fourmile <br />Canyon Creek and Wonderland Creek. Spill flow discharges leaving Fourmile Canyon <br />Creek model are hard coded into the spill area model at appropriate locations in the <br />model. The spill area does not have a well defined channel, and the paths and outer <br />limits of the spill were identified by drawing velocity vectors perpendicular to the <br />topographic (equipotential) contours. In general, it appears the spill path downstream of <br />Broadway for all events will generally follow street~ and only shallow flooding is <br />anticipated in most of the spill area. <br /> <br />A schematic of the spill area modeled in HEC-RAS is shown on Figure 2. As shown on <br />the schematic, flow divisions were identified in the spill area, and these areas were <br />modeled in HEC-RAS. Flow divisions were modeled using energy-based methods at <br />junctions, following recommendations in the HEC-RAS manual. Flows upstream of <br />Broadway leave the channel and cross Broadway. Just south of Upland Avenue, <br />represented by Junction 2 in HEC-RAS, the flows split, and approximately 80 percent <br />flows southeast towards and into Wonderland Creek while the remainder flows <br />eastwardly. The eastwardly moving flows split again near Crestview School, represented <br />by Junction I in HEC-RAS. At Crestview School, most of the remaining spill flows <br />southeast toward Wonderland Creek, while a small portion returns to Fourmile Canyon <br />Creek. <br /> <br />After reviewing routing issues and simplifications made in the hydrologic and hydraulic <br />analysis with the City and UDFCD, it was decided not to add the minor flows which <br />return to Fourmile Canyon Creek to the HEC-RAS model discharge. Thus, the main <br />channel model of Fourmile Canyon Creek with the split flows leaving the model at <br />Broadway is used to define the hydrology of the Creek downstream of the split flow <br />reaches. <br /> <br />3.2.1.2 Flow Division at 61st Street <br /> <br />The 61 st Street crossing of Fourmile Canyon Creek is located near its confluence with <br />Boulder Creek. As discussed in the following section, the culvert below 61 st Street in the <br />main channel is assumed to be completely blocked by debris for the purpose of the <br />LOMR. As a result, flood flows overtop 61 st Street. Most of the flood flows continue to <br />the west along the left overbank of the channel, eventually entering a lake and Boulder <br />Creek. A small percent of the flows enter the main channel. The flow division was <br />modeled in HEC-RAS using energy-balance methods. <br /> <br />-14- <br />