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4 m I I r I ~ I r I I I I t r L I I l ~ TABLE 1. - SUMMARY OF DISCHARGES'IJ Flooding Source and Location Drainage Peak Discharge Area (cfs) (Sq. I 0- year 50-year I 00- year 500-year Miles) At Confluence with Canyon 45 820 1,280 1,680 2,480 Creek At Confluence with Cascade 75 1,280 1,940 2,590 3,800 Creek At Downstream Corporate Limits not 1,330 2,040 2,720 4,000 available NOTES: (I) Federal Emergency Management Agency, Flood Insurance Study, City of Ouray, Colorado, Ouray County, July 3, 1985. Hydraulic Analysis . . Hydraulic analysis for the model development and for the proposed project were conducted using the U.S. Army Corps of Engineers (US ACE) HEC-2 computer program. The approach taken for these tasks are described below. Model Development - The original HEC-2 model, used to define the floodplain in the Floodplain Information Report for the Uncompahgre River (Reference I) was not available. Discussions by CWCB personnel with engineers who performed the original work identified that cross section information was digitized by the mapper. However, no records of the model or cross-section data could be found. Research into CWCB files resulted in a blue-print of the original 1"=200', 5' contour interval topographic mapping ("blue-prints"), which was used for the model development, as described below: A. The location of the original cross sections were identified on the blue-prints using the Floodplain Information Report. Elevations and stations were read and recorded (note: This information was provided by the CWCB and was checked and modified during the course of the work.) B. Cross section information was plolted on work sheets. The thalweg invert and the floodplain width from the Floodplain Information Report were used to adjust the channel invert and the width of the section at the 100-year water surface elevation.