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-1- PREFACE "100- year flood" and "one percent fl ood" c an be used i nterch angeab ly as they all define the same type of flood event. AUTHOR IZA T1 ON This report was authorized by the Urban Drainage and Flood Control District which makes floodplain information and mapping available to local agencies enabling them to adopt and administer their own floodplain regulations with the assistance of the District. The Urban Drainage and Flood Control Dis- t ri ct has the power to enact di s tr i ct-wi de fl oodp 1 a ins incases where local governments fail to enforce their own regulations. PURPOSE AND SCOPE This report was prepared by Wright Water Engineers for the guidance of local officials in planning the land use and. regulation of the floodplain. The report includes information on past floods and the nature and extent of probable future floods which can be reasonably expected on the respective study reaches. The 100-year flood should be given appropriate consideration before planning for development in the floodplain. The Colorado Water Conservation Board has the power and duty "... to designate and approve storm or floodway runoff channels or basins, and to make such designations available to legislative bod- ies of cities and incorporated towns; to county planning commis- sions; and to boards of adjustments of cities; incorporated towns; and counties of this state..." as stated in Section 37-60-1-6 (1) (c) of the Colorado Revised Statutes 1973. The cities, incorporated towns and counties within the study area may provide 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 or basin has been designated and approved by the Colorado Water Conservation Board, in order to lessen or avoid the hazards to persons and damage to property resulting from the accumu- lation 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. The 100-year floodplain is shown on the Flood Hazard Area Delineation Maps which delineate the areas that would be inundated by such a flood event. Flood profiles show the water surface elevations relative to the stream bed. Elevation reference data is given that can be applied across the full width of the river valley. Valley cross sections are presented to indicate ground 1 evel across the valley at speCified locations and the overlying flood depths. The fl ood prof il es and flooded area dat a presented are based on future, developed conditions in the basin as determined from current master p 1 anni ng maps. Poss ib 1 e future improvements to control floods are not a consideration of this report. The information contained in this report does not imply any state action to zone or regulate the use of the flOOdplain. The Urban Drainage and Flood Control District has the authority to regulate floodplains, but has chosen to leave floodplain regulation responsibility with local governments. This report provides a suitable basis for the adoption of land use controls to guide floodplain management, with consideration for environmental attri- butes, and thereby prevent intensification of flood losses. Upon acceptance of this report by the Urban Drainage and Flood Control Dis- trict and the designation and approval of this report by the Colorado Water Conservation Board, the areas described as being inundated by the 100-year flood can be designated as flood hazard areas and their uses regulated ac- cordingly. It should be noted that the terms "Intermedi ate Regional Flood," Flood water surface elevations and flOOdplain boundaries are often revised by road and bridge construction, floodplain development, flood control im- provements, or natural processes. Prior to utilization of this report for planning or design purposes, the user is advised to contact the Urban Drain-