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I I I I I I I I I I I I I I I I I I I TODD CREEK FLOOD HAZARD AREA DELINEATION - PURPOSE AND SCOPE - - AUTHORIZATION - This report was prepared to guide 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 an approximate 10.9 mile study reach of Todd Creek and the other studied tributaries. This study was prepared under the current format of the District's Flood Hazard Area Delineation Reports. The study scope consists of an analysis of the 10-, 50- and 100-year flood events. This report was authorized and contracted through the Urban Drainage and Flood Control District (UDFCD) as part of a program identifying floodprone areas within the District's jurisdiction. Thi s study i dent ifi es floodprone areas along Todd Creek and four unnamed tributaries within the Todd Creek drainage basin. The majority of the study area is within unincorporated Adams County. However, both the City of Thornton and City of Brighton plan future development within the drainage basin. The floodplain information included in this report is provided by the UDFCD to enable local governments to adopt and administer comprehensive floodplain management regulations. Included in this report are Flood Hazard Area Maps which show the areas that would be inundated by the 100-year flood event. The water surface profile shows the 100-year flood elevations along the channel related to Mean Sea Level (MSL) Datum, also referred to as National Geodetic Vertical Datum (NGVD). The report also includes information regarding the channel thalweg, existing drainage structures, stream bank elevations where appropriate, typical floodplain cross sections and flood flow characteristics. Upon acceptance of this report by the UDFCD, and the designation and approval of th~ flood hazard areas by the Colorado Water Conservation Board, thi s study can be used by the City of Thornton, the City of Brighton, and Adams County to regulate future floodplain construction, to guide future drainageway improvements, and to plan flood protection measures along the channel and floodplain of the studied streams. A floodway was also computed as part of this study based on criteria specified by the UDFCD (maximum 0.5 foot rise on the energy grade line assuming equal conveyance reduction on both sides of the floodplain). Floodplain and floodway data, including widths, elevations, velocities and reference data, are presented in Table V of this report. The floodway is provided to designate those areas to be kept free from future encroachment and reserve an area for conveyance of the 100-year flood. Floodway criteria are intended to limit future increases in flood stage and velocity resulting from floodplain development. The flood profiles and floodplain delineation presented in this report are based on existing floodplain and channel conditions, with future 1