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I I I IV. OUTFALL SYSTEM EVALUATION AND DESIGN Reach F-I - The channel is to be diverted southeasterly into Reach G-I instead of north along U,S. 287 to Coal Creek. Reach G-I - The alignment is to be shifted southward to avoid the farmhouse along U . S. 287, I A. Alternative Evaluation I I The study area was divided into ten major drainageways or outfall channels. These drainageways were then divided into 3i channel reaches for development and evaluation of drainage improvements. The categories of improvements investigated included status quo, selected structural, grass channel, riprap/concrete channel, storm sewer, regional detention, and relocation or diversion. Each reach was evaluated for all categories, The evaluation ranged from a preliminary design and cost estimate to a cursory review of the technical feasibility. Reach G-II - The alignment to follow along the south edge of the pavement of Dillon Road, I Reach I-I The alignment to be diverted south along 104th Avenue instead of throu; Stearns Lake. I The final alignment is presented in schematic form on Drawing No, 4 and the outfall design is presented on Drawings-a to -36 of this report. I A complete matrix of the alternative outfall systems investigated is presented in Appendix A. For each reach and alternative category, the results of the evalua- tion are listed. Those categories labelled IINo" indicate where the alternative was deleted from the matrix and includes a discussion of the justification for not further evaluating the alternative. Those categories labelled "Yes" indicate the alternatives that were evaluated in detail. The cost of the alternative for that reach is listed and the consultant recommendation is noted by an asterisk. A summary of the consultants recommendations is also presented ~n the Appendix A. B. Design Criteria I I I The outfall system evaluation was presented to the City of Louisville council at a work session on March 23, 1982, The consensus of the Council was to direct Water Resources Consultants, Inc. to proceed with the preliminary design of the outfall system. Subsequently, the technical advisory and Water Resources Consultants, Inc. met and selected the final system alignment. Alignment changes in the Outfall Systems were made as follows (Note: see Appendix A for reach definition): The design basis for the Outfall System Planning was prepared under Criteria Development Phase of this study (see Section I-B). The City of Louisville "Storm Drainage Design and Technical Criteria" published as the result of the Criteria Development Phase and supplemented by the Urban Storm Drainage Criteria Manual (Reference-2) were used to prepare the preliminary design of the Outfall System. The major components of the Outfall System are open channels, check drops, storm sewers, culverts/bridges, detention ponds, and irrigation ditch crossings. The design specifics for these facilities are described below. I I I Reach A-I - The channel is to be combined with the channel proposed by 1n the report "Major Basinwide Planning City of Lafayette/Boulder County", December, ]980 along Centaur Villages. I. Open Channels Open channels were included in the Outfall System where the storm runoff flows exceeded allowable street flow limits in areas of open space land use and through residential areas, All grassed channels are designed for the ]00- year flood peaks and include a 4-foot wide concrete trickle channel and a ]2- foot wide maintenance access road. The maximum ]OO-year flow depth is 5-feet plus a minimum of I-foot freeboard. The maximum 100-year flow velocity of 7 fps was used to establish the channel grade, and in certain instances, flatter slopes were specified to better match the natural grade, I I Reach D-II - The alignment proposed for the Heritage Development will be used as a guideline, I I -]3- -14-