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2 SECTION I INTRODUCTION Urban Drainage and Flood Control District and the City of Lakewood GENERAL PLANNING STRATEGY The Urban Drainage and Flood Control District (UD&FCD) and the City of Lake- wood have identified South Lakewood Gulch as a high-priority item in the cOn- tinuing program of preparing master plans 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 and the various governmental entities are in- creased. At the same time, the public will be able to enjoy recreation and other auxiliary benefits which would not otherwise accrue. This report was prepared for the guidance of local officials in planning the use and regulation of the floodplain. The 100-year floodplain has been delineated for future basin conditions with the existing channel and is shown on Sheets 1 through 7 at the back of this report. 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 objec- tives such as economic development, regional development, transport, social well-being and environmental quality. Because these resources are limited, and the demands are not I imited, these objectives compete with one another. In terms of drainage, competing objectives must be considered and reconciled through a formal planning strategy. A planning strategy contains goals and objectives and provides a pol icy. Federal and State Laws 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. Drain- age must be viewed as one of many issues affecting the use of land in the metropolitan area. While floodplain areas can provide recreational oppor- tunities, all recreation areas should not be dependent on drainage con- siderations. 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 Flood Plain Regulation, prpvide 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. Study Procedure Drainage basins are convenient units for water resources management pur- poses. Within the boundary of each drainage basin, a system of water- courSeS has evolved which is specifically related to its physical and hydrologic condition. The watercourses, and the floodplains developed through periodic inundations, are the primary areas of consideration in drainage basin management. However, to mitigate flood losses, control erosion, manage sedimentation, and abate water pollution, it is necessary to formulate management pol icies not only for the watercourses and flood- plains, but also for all parts of the drainage basin. The fi rst step toward producing this report was to identify the goals and objectives. The consultants interviewed parties affected by the drainage and flood control program and found their goals and objectives to be con- sistent with the goals of the UD&FCD. One goal is to maintain the natural historic character of the upper part of the floodplain. Field surveys and library research were conducted to gather information relevant to the physical characteristics of the existing drainage basin; The consultants visited South Lakewood Gulch and inspected the hydrologic and surface characteristics in terms of topography, vegetation, soil, geology, and stream characteristics. Land use and future development fore- casts were provided by the City of Lakewood. The results of this data gather- ing process are detailed in this report. Floodplain Description Precipitation information was obtained from the Drainage Criteria Manual (Ref. 1) to determine the design rainfall event(s) that would be used for runoff analysis. Soils data were provided by the Soil Conservation Service. 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 include part of the steeper valley slopes. It is periodically inundated in part or totally, depending on the magnitude of the floods. The prob- ability of inundation is an important concept in drainage basin manage- ment. The floodpla:n 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 1 percent chance of occurring in any 1 year (the 100-year flood). The next step in applying the Drainage Criteria Manual was to analyze and eval- uate the data that had been gathered. The evaluation included development of a hydrologic computer model for flood hydrograph generation. (Ref. 2). I'