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I I I I I I I I I I I I I I I I I I I - PREFACE - The lOa-year floodplain is shown on the Flood Hazard Area Delineation Maps (Sheets 1-21) which indicate the areas that would be inundated by this flood event. Flood profiles (Sheets 22-29) show the water depths relative to the normal low water level during winter months for the lOa-year and la-year flood events. Water surface elevations are provided at each channel cross section in Tables I & II. These elevations indicate a constant water depth across the full width of the stream valley. Valley cross sections are plotted on the profile sheets at specified locations with water depths during the lOa-year and la-year events shown on the drawing. The flood profiles and flooded area data presented are based on future, developed conditions in the Clear Creek basin. Possible future improvements to con- trol floods are not a consideration of this report. The information in this report does not imply any state action to zone or regulate use of floodplains. The District has the author- ity to regulate floodplains, but to date has chosen to leave flood- plain regulation responsibility with local governments. The report provides a suitable basis for the adoption of land use controls to guide floodplain management, with consideration for environmental attributes, and thereby prevents intensification of flood losses. Flood water surface elevations and floodplain boundaries are often revised by road and bridge construction, floodplain develop- ment, flood control improvements or natural processes. Prior to utilization of this report for planning or design purposes, the user is advised to contact the Urban Drainage and Flood Control District to determine if the information in this report has been amended. Authorization This report was authorized by the Urban Drainage and Flood Control District and Adams County. At present, the District joins with local communities to make floodplain information and mapping available for local governments to adopt and administer their own floodplain regulations with the assistance of the District. The cities, incorporated towns, and counties within the study area may adopt these zoning regulations. "....to establish, regulate, restrict and limit such uses on or along any storm or floodwater runoff channel or basin, as such storm or floodwater runoff basin has been designated and approved by the Colorado Water Con- servation Board, in order to lessen or avoid the hazards to persons and damage to property resulting from the accumulation of storm or floodwaters...." as stated in Section 30-28-201 for county governments and Section 31- 23-201 for municipal governments of the Colorado Revised Statutes 1973. Upon acceptance of this report by the Urban Drainage and Flood Control District and the designation and approval of this report by the Colorado Water Conservation Board, the areas de- scribed as being inundated by the 100-year flood (Intermediate Regional Flood) may be designated as flood hazard areas and their use regulated accordingly. It should be noted that the terms "Intermediate Regional Flood," "lOO-year flood," and "one percent flood" can be used interchangeably as they all define the same magnitude flood event. Acknowledgements This report was prepared by Gingery Associates, Inc., Con- sulting Engineers, Englewood, Colorado, at the request of the Urban Drainage and Flood Control District and Adams County. The topo- graphic mapping included in this study was prepared by Bell Mapping Company of Denver, Colorado (Reference 1). The U.S. Army Corps of Engineers, Omaha District, provided the revised flood discharges which were used in this report. Purpose and Scope This report was prepared for the guidance of local officials in planning the use and regulation of the 100-year floodplain. The report includes information on past floods and the nature and extent of probable future floods along the study reach. The 100-year flood should be given appropriate consideration before planning for develop- ment in floodprone areas. -1-