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I I I I I I I I I I I I I I I I I I I V-2 Alternatives Evaluated Numerous alternatives, some studied in the previous master plans, were evaluated during the course of the Phase A study. These ranged from doing nothing to detention and channelization. The evaluations consisted of determining the damage reduction associated with the improvements, estimat- ing the cost associ ated with the construction of those improvements, and calculating a benefit/cost ratio. In addition to this quantitative analy- sis, a qualitative analysis which stressed intangible benefits was also performed. Both these analyses were considered in developing the recom- mended plan. The initial alternatives evaluated were: 7. Combinations. This involved primarily combinations of detention and channelization to bring the total level of protection to some predetermined level. 1. Do Nothing. This alternative involved doing nothing to the flood- plain or channel, but leaving conditions as found at the onset of the study. This was the baseline against which all other alterna- tives were evaluated. The Phase A Recommended Plan The rehabilitation of Leyden Reservoir is a principal element of the recom- mendations made by Wright Water Engineers during the Phase A Master Plan- ning process. Maintaining Leyden Lake provides for a reduction in flow rates along the entire length of Leyden Creek downstream of the lake and on Ralston Creek downstream of its confluence with Leyden. This results in a reduction in damages worth approximately 5 times greater than the cost of the improvements. 2. Leyden Reservoir. This alternative consisted of the repair and rehabilitation of the embankment and spillway of Leyden Lake. The Oak Street Detention facility is part of the recommended plan. These off-channel detention ponds reduce flows along Van Bibber Creek to those associated with the 15-year historic flood. The facilities are multi-use and would allow for the continued use as soccer fields. Among the benefits are the ability to use the embankments of the detention facilities as spec- tator seating, the elimination of the stigma of continued flood hazard through the Arvada Plaza Shopping Center, and the continued utilization of the previously constructed improvements along Van Bibber Creek north of 58th Avenue. 3. Ward Road Reservoi r. Thi s altern at i ve cons i sted of the construc- tion of Ward Road Reservoir as previously designed. 4. Oak Street Detention Facility. This alternative consisted of the construction of five off-channel detention facilities located in or near the Arvada Soccer Association soccer complex. 5. Ten-Year Channelization. This alternative consisted of the con- struction of 2-year channel sufficient to convey the 10-year event through areas experiencing significant flood damages. Channel improvements along Ralston Creek and Leyden Creek are to be made to the 10-year flood with Leyden Lake in place. This level of protection is both cost effective and affordable. While the design differs significantly from the previ ous Master Pl an recommend at ions, it was concl uded that the reduced facility size enhanced the likelihood of implementation. Because of the freeboard requirements and other constraints imposed by existing features, the lOO-year event is to a 1 arge extent, conveyed withi n the channel R.O.W. in most cases. This provides an increase in the damage re- duction without a commensurate increase in costs. One of the goals of this 6. 100-Year Channelization. This alternative consisted of the con- struction of a channel sufficient to convey the 100-year event through areas experiencing significant flood damages.