Document Type

Report

Publication Date

January 1976

Abstract

A generally applicable hybrid computer program is developed to simulate runoff from urban watersheds, and is applied to represent the outflow hydrographs of three urban watersheds located within Salt Lake County, Utah. The gaged outflow of the watersheds provided a means for comparing the observed and the simulated final outflow hydrographs. Each of the three watersheds was subdivided into spatial units or subzones, and the outflow hydrographs for each subzone were obtained by abstracting interceptions, infiltration, and depression storage from the rainfall hyetograph of each subzone. The resulting hydrograph outflow of each subzone was routed to the Jordan River, the final outflow point of the three watersheds. The final hydrographs of the three watersheds were combined and compared with the gaged flow. The unique features of this model are its ability to (1) accept a wide range of input hyetographs, (2) accommodate variable loss rates, (3) combine subzone hydrographs, and (4) combine watershed hydrographs into a single runoff function. In addition to numerical output, graphs can be plotted for visual inspection. This characteristic enables designers and planners to use the model to examine quickly both the physical and economic impacts of various possible input conditions and management alternatives. An economic analysis follows the hydrologic study. Areas subject to flooding within the study watersheds were mapped and measured in accordance with peak discharge rates. Flood damages per unit area were estimated as a function of degree or urbanization. Projected population growth within the area is used as a basis for estimating the rate of urbanization of the next 100 years. The utility of the procedure (which depends heavily upon the hydrologic model) for design and planning purposes is demonstrated through an example of a benefit-cost analysis which is applied to a proposed flood control structure within a portion of the study area. The study emphasized that reliable planning and management solutions from the modeling approach depend heavily upon the availability of adequate and accurate field data. For this reason, “barometer” urban hydrology watersheds situated at strategic locations throughout the nation would provide invaluable information for the broad application of this procedure. In addition, it is considered that future work also should emphasize the expansion of the model to include the economic dimension, and ultimately various aspects of the social dimension.

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