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I I I I I I I I I I I I I I I I I I I I 34 Detention pond locations were examined for each of the major flow paths. One site was identified within the Central Basin which has generally favorable site constraints, and which could effectively reduce the flows tributary to the City Park box culvert. From the flow reduction standpoint, a pond sited north of the intersection of Otero Avenue and 7th Street is desirable. The land where the pond would be sited is privately owned and would have to be acquired at fair market value. An alternative pond site located at Otero Avenue (extended) and 11th Street also has favorable technical charac- teristics. On-site detention as a means of reducing future storm water management costs was evaluated. Several proposed single-family residential projects woul d be tributary to storm drainage facilities, and would have to assist in their financing and construction. It may be economically feasible for a deve- loper to construct a detention pond to control the peak rate of runoff from thei r development to hi stori c 1 evel s. The cost of tile pond and outl et struc- ture may be less than a developers "pro rata" share of for instance, a pipe or culvert system. The feasibility of on-site detention will be dependent upon the value of the land, and the density required to make a given land develop- ment project profitable. Figure 9 presents a detention system concept within the Central Basin. Evaluation of Alternatives Presented on Tables 9, 10, and 11 are cost estimates for each alternative presented on Figure 7, 8, and g. The cost for the 10- and 100-year frequency designs were estimated to provide the range of costs related to the reduction in flood threat. Cost for utility relocations and right-of-way acquisition have not been considered in the cost estimates, except for the land associated with the pond presented in the detention alternative. General assumptions made in the development of each of the alternatives \~ere: 1. Future development conditions exist. 2. Full conveyance of flows from the Northwest Basin by the Northwest Drainageway would be provided. 3. No effective conveyance or diversion of storllMater by irrigation laterals exists.