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I I I I I I I I I I I I I I I I I I I I. Relocation of the channel to routes other than the historic channel. J. Other plans as suggested by participating entities. K. Combinations of the preceding. Benefit/Cost Analysis Duri'l: Phase A, a benefit/cost analysis was completed which served to identify the relative economic merits of each alternative. How well each alternative satisfied the other objectives of the study was a matter of judgment, since no attempt was made to rate the alternatives on any quantifiable criteria other than economics. The annual dollar amounts for flood induced damages were estimated for the existing channel condition. The benefits, which reflect the reductions in the average annual flood damages resulting from the construction of the project, were quantified and compared to the associated improvement costs for each alternative plan. The benefit/cost analysis included an incremental analysis performed to determine the optimum design flood for the given facility. The unit costs and procedures utilized are described in Section VI of the Phase A report. Selection of Recommended Plan Because each channel reach presents a unique problem alternative flood control plans were considered on a reach by reach basis. Alternative flood control plans are identified by reach in an alternative matrix, Figure IV-I. Preliminary examination of each alternative plan led to the elimination of those shown in the shaded sectors of the matrix as being infeasible for practical application. Discussion of the feasibility of each of the alternatives is in the Phase 'A' Report. The alternative flood control plans which appeared to be most promising are listed by reach in Table IV-2. Examination of the floodplains and benefit/cost data lead to the determination of those alternative plans for each reach which were the overall most economically beneficial. Due to the numerous reaches and widely varying existing conditions, selecting one plan for implementation on Little Dry Creek strictly on the basis of the benefit/cost analysis would not have been a good approach because the other study objectives would be ignored and an incoherent master plan may have resulted. Therefore, a systems approach was utilized for the final plan selection, whereby reaches were combined and the alternative plans with common characteristics were chosen and examined as a unit. For the systems analysis, the reaches were combined into three groups: Reaches 1, 2 and 3 in Adams County and Westminster; Reaches 4 and 5 in Arvada and Jefferson County; and the Shaw Heights Tributary in Westminster. On the basis of the foregoing analysis, the consultants recommended a combined alternative plan, as outlined in Section I of the Phase 'A' Report, of channel improvements designed for a 10-year event in IIl- 2 Reaches 1,2, and 3; channel and detention pond improvements designed for the 100-year event in the Shaw Heights Tributary; and continued flood plain management and regulation in Reaches 4 and 5. Legal Review The Phase 'A' Report was reviewed by Edward J. Krisor of Shoemaker and Wham, Attorneys-at-Law, and his comments to the Urban Drainage District are included in Appendix B. TABLE N-l FLOOD DAMAGE BY JURISDICTION Average Annual Damage Jurisdiction Reaches By Reach 168,600 + 54,030 Total Present Worth 222,630 3,224,480 11,820 171,200 280 4,055 135,950 1,969,040 188,975 2,737,040 559,655 8,105,815 Adams County 1 and 2A = Arvada 4 and 5 10,940 + 880 = Jefferson County 5 280 = Westminster 2B and 3 45,880 + 90,070 188,975 = Tributary "A" = TOTAL