Disaggregated Modeling for Urban Hydrologic Controls

A wide variety of best management practices (BMPs) are available for controlling urban stormwater quantity and quality. In-situ controls and low impact development (LID) methods and materials provide a distributed network of onsite stormwater control. When trying to implement onsite controls in an urban environment, runoff volume control must be performed within spatial constraints and it can be difficult to determine the net control of decentralized BMPs within a watershed. The paper illustrates a tool that quantifies the net effect of onsite control methods in subcatchments ranging from 0.01 to 7 acres. The methodology presented herein steps through transforming data into a usable geographic database, transferring data from the geo-database to a hydraulic/hydrologic modeling program, and evaluating BMP performance by manipulating functional land unit parameters. Results indicate that, under such a disaggregated examination, BMP functions are ubiquitous only varying in degree, serving as control areas as well as sources of runoff in what can be a long chain of storage-infiltration-runoff steps. These disaggregated BMP functions can be represented explicitly by simulating a parcel or catchment at the functional unit scale, capturing the spatial reality of the catchment while still providing an approach to modeling the net control of a larger watershed.