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<br />Table 6. Summary of UDSWM node and HECRAS Upstream Cross Section <br />Defining the Discharge at the Location <br /> <br />Location UDSWM Node HEC-RAS Upstream <br /> Cross Section <br />Fourmile Canyon Creek <br />Upstream Study Limit 310 500 <br />Broadway 402 484 <br />19tn Street 312 441 <br />28th Street - 370 <br />SH 119 313 250 <br />Confluence Boulder Creek 314 125 <br />Wonderland Creek <br />Wonderland Lake Outfall 420 19300 <br />Broadway 250 18770 <br />Between 15th and 19th St. 240 16915 <br />19th St. 230 15695 <br />28th St. 212 8425 <br />4ih St. 210 3635 <br />Confluence Goose Creek 200 860 <br /> <br />The Appendix also contains a copy of the frequency analysis used to identify the 500- <br />year event. <br /> <br />3.2 Hydraulic Analysis <br /> <br />HEC-RAS Version 3.1.1 (USACE, 2003) was used to define flood elevations and <br />floodplains of Fourmile Canyon Creek and Wonderland Creek for the LOMR. A LOMR <br />is required because (1) The model is based on new topographic mapping (Merrick, 2003) <br />and survey information (GeoSurv, 1998, Flatirons Survey, 2003, Scott, Cox & <br />Associates, Inc., 2003, and Robert Sayre, 2005). Where conflicts exist between the <br />mapping and survey data, the land survey information is used. <br /> <br />Survey information was collected using different vertical datum, and all survey was <br />converted to NA VD 1988. The vertical datum for the topographic mapping and for the <br />LOMR is NA VD 1988. Work maps are presented in Appendix 5. <br /> <br />The hydraulic models are run assuming subcritical flow conditions, and the starting water <br />surface elevations were obtained from regulatory models. The HEC-RAS models for the <br />two streams indicate major segments of both streams flow at critical depth, the result of <br />steep channel slopes. <br /> <br />-12- <br />