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I c I I SECTION I INTRODUCTION I This report was prepared for the guidance of local officials in planning the use and regulation of the floodplain, The lOO-yearfloodplain has been delineated for future basin conditions with the existing channel and is shown on Sheets 1 through 32 in Section IV of this report, Floodplain Description A floodplain is generally a smooth, or relatively flat area bordering a stream, which is built of sediments carried by the stream, but may also in- clude part of the steeper valley slopes. It is periodically inundated in part or totally, depending on the magnitude of the floods. The probability of inundation is an important concept in drainage basin management. The flood- plain can be defined as the area subject to flooding. The usual reference is to the floodplain resulting from the flood which is estimated to have a I percent chance of occurring in any I year (the IOO-year flood). I I GENERAL PLANNING STRATEGY I There are many demands on the land and water resources of an urban region. The demands are associated with efforts to achieve a variety of objectives such as economic develop~ent, regional develcp~ent, transport, social well- being and environmental quality. Because these resources are limited, and the demands are not limited, these objectives compete with one another, In terms of drainage, competing objectives must be considered and recon- ciled through a formal planning strategy. A planning strategy contains goals and objectives and provides a policy, ~I I Within this context, demands for the land and water resources can be ordered in terms of their ability to achieve desired goals and objectives. This is a device that can be used in the decision-making process, Drainage must be viewed as one of many issues affecting the use of land in the metropolitan area. While floodplain areas can provide recreational opportunities, all recreation areas should not be dependent on dr2inage considerations. Urban Drainage and Flood Control District and Local Government The Urban Drainage and Flood Control District (UD&FCD) and the Cities of Broomfield and Westminster have identified the subject basins as high priority itemsin the continuing program offloodplain delineations for major drainages. It has been concluded that corrective measures and master planning are needed now, before additional mistakes are made, It is a well-established fact that through early-act ion-projects, corrective costs can be substantially reduced. As a result, the benefits to society aod the various governmental entities are increased, At the same time, the public will be able to enjoy recreation and other auxiliary benefits which would not otherwise accrue. I I I I I Drainage basins are convenient units for water resources management purposes, Within the boundary of each drainage basin, a system of watercourses has evolved which is specifically related to the physical and hydrologic condi- tions. The watercourses, and the floodplains developed through periodic inundations, are the primary areas of consideration in drainage basin manage- ment. However, to mitigate flood losses, control erosion, manage sedimenta- tion, and abate water poilution, it is necessary to formulate management policies not only for the watercourses and floodplains, but also for all parts of the drainage basin. yederaJ and State Laws The Flood Disaster Protection Act of 1973 (PL 93-234), the Water Resources Development Act of 1974 (PL 93-251), and HB 1041 of the State of Colorado, under which the Colorado Water Conservation Board promulgated a Colorado Model Floodplain Regulation, provide significant new constraints to flood- plain development and opportunities for floodplain management. Full imple- mentation of these laws and related regulations will tend, over the years, to improve the cost-effectiveness of those alternatives which are based on nonstructural solutions, or for the improved floodplain. I I I I I