Evaluation of Catchment-Scale Efficiency of Green Infrastructure in an Urban Watershed through Process-Based Modeling

In urbanized watersheds, one or two inches of rainwater can result in significant amount of surface runoff. Stormwater green infrastructures (GI)s are being widely used to reduce volume and peak of surface runoff or its pollutant level through increasing infiltration, evaporation, filtration or just delayed release to the traditional sewer systems. To evaluate the cost-effectiveness of the GI practices, it is important to be able to predict their collective impacts at catchment scale while considering the processes occurring within individual GIs. In this presentation, we will show the application of a newly developed modeling system (GIFMod) to predict the long-term impacts of GIs on the hydrologic response of a highly urbanized watershed Sligo Creek, MD. In GIFMOD the watershed can be represented using a number of connected blocks representing sub-catchments, the unsaturated soils and groundwater beneath each sub-catchment and a network of streams. The soil columns underneath each catchment is discretized into several layers to more accurately capture infiltration and percolation processes. The overland and stream flow are modeled using diffusive wave model and the unsaturated flow in soil is modeled using Richards equation. The pre-retrofit version of the model is calibrated using observed hydrographs over a period of one year stochastically through an MCMC algorithm (figure 1). The parameter values estimated is used to evaluate the post retrofit conditions of the catchment while considering multiple scenarios of GI implementation. Each individual GI is implemented into the model with high level of details and accurately considering the drainage area contributing into them.