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Water Reservoir Systems were investigated for urban areas as an alternative or complement to storm water drainage systems for flood control which could provide benefits in water conservation and reduce drainage system costs. The study consisted o f (1) gathering of engineering data on the topographical, hydrological, and precipitation characteristics of the area and urban development and economic statistics; (2) designing a water reservoir system for the Santa Maria area and a comparative conventional storm water drainage system; (3) evaluating the economics, costs and benefits of the reservoir system with comparison to a conventional storm drainage system; and (4) projecting the Santa Maria study results to other urban areas.(KEY WORDS: water; reservoir systems; urban; flood control; water conservation; storm water; drainage) GENERAL Water reservoir systems were specifically evaluated for Santa Maria, California, a community of approximately 35,000 people in an agrarian section of the southwest, bordering on the Pacific Coast with a relatively flat topography, semi-arid climate including seasonal rainfall of approximately 14 inches annually. The area is also characterized by high soil infiltration rates, a falling water table with an urban area that includes some highly urbanized acreage, undeveloped but planned urban development acreage and residual agricultural acreage within the urban boundaries. The total Santa Maria area considered for drainage was 12-square miles with the flooding problem of paramount interest to the community covering principally the highly urbanized area of downtown. The Stanford Watershed Model was used to carry out computer analysis of the watershed behavior.It is evident that the Santa Maria characteristics are relatively unique and indigenous to southwest coastal areas. However, application of the Santa Maria study to other urban areas throughout the nation can be done in terms of parametric considerations that have been developed or confirmed by the Santa Maria evaluations. The characteristics of prime importance in evaluating a drainage system are relatively few and include: precipitation-frequency, amount and intensity; terrain-flat, sloping or hilly; soil infiltration; extent of urbanization including size and values; flood damage; value of water conservation; planned urban development; and repositories for storm waters-length of trunk lines, settling basins or river basins, etc. These parameters have been analyzed in the Santa Maria study. General guidelines were developed from the Santa Maria analysis and are presented as individual parametric effects on Paper No. 71031 of the Water Resources Bulletin (Journal of the American Water Resources Associa-1 tion . Discussions are open until sir months from date of publication.