Evaluating Distribution of Stormwater Green Infrastructure on Watershed Outflow

Authors

Benjamin Fahy - Portland State University, Heejun Chang - Portland State University Geography Department Chair and Graduate Student Adviser

Body

Stormwater Green Infrastructure (SGI) has become an increasingly popular method for flood mitigation for the ability to reduce overland runoff in flood prone urban settings. The spatial distribution of SGI remains topic for debate; the hydrologic benefits and economic costs associated with dispersed versus centralized SGI is relatively unknown. We compared adjacent subcatchments with differing SGI arrangements (lot-level rain gardens, detention ponds, centralized facilities, and no treatment) in the City of Gresham, Oregon. Using the EPA Stormwater Management Model (SWMM), we simulated rain events and compared impacts of SGI distribution on runoff outflow using four different indices (peak flow height, lag time, flashiness, and discharge quantity). We used hourly precipitation and pipe flow data to calibrate the model to historical storms, and altered how flow is routed through SGI to compare and identify best practices for promoting detention and infiltration of stormwater. We hypothesized that catchments with dispersed SGI (lot level rain gardens) exhibit lower peak discharge, longer lag time, less flashiness, and less total discharge than all other arrangements. This research will serve as a basis for understanding how modelling runoff at high resolutions can yield useful information to city planners and developers seeking effective and cost-efficient solutions when implementing SGI in urban stormwater management practices.
Keywords:Stormwater, Green Infrastructure, LID, bio-retention, retention, storm water management, SGI

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