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. . Mr. Richard W. Krimm August 18, 1977 Page two Gingery Associates is presently completing, for the Urban Drainage and Flood Control District and the Colorado Water Conservation Board, a flood hazard area study of the South Platte River in Adams County, including Commerce City. This flood hazard area study is based on final corps of Engineers' hydrologic data, detailed 2-foot contour interval maps, and additional cross-section data. Gingery Associates received "Notice to Proceed" with this study on September 22, 1976. A recent review of the study results, attended by Mr. Wayne Graham of the regional Federal Insurance Administration office, indicated that the final 100-year discharge is as much as 5,000 cfs higher than the discharge in the FIA's study and that the 100-year water surface elevations vary by as much as 5 feet from the FIA's study. In the Commerce City area, the maximum difference in water surface elevations is about 5 feet. The Colorado Water Conservation Board is required by state statutes to designate and approve all floodplain studies before local governments can legally enforce appropriate floodplain management regulations. The Board is therefore greatly concerned with designating and approving technically accurate and up-to-date studies. Publica- tion of two studies for the same study area, with significant differences in discharge and water surface elevations, will damage the credibility of all local, state, and FIA studies. Because the Urban Drainage and Flood Control District's study is based on up-to-date hydrologic data, detailed topographic mapping, and additional cross-sections, it is technically much more accurate than the FIA's study. The Colorado Water Conservation Board will therefore not designate and approve the FIA's study. The UD&FCD's study will be completed early in September and will be designated by the Colorado Water Conservation Board either at its September 16, or November 16, 1977, meeting. We therefore advise that the Commerce city Flood Insurance Study be revised.