Optimizing the Placement of Low Impact Development in an Urban Watershed

An increase in urbanization adversely impacts the health of watersheds and receiving water bodies, causing increased peak flows, runoff volumes, velocities and erosion along the banks of a stream. Low Impact Development (LID) methods are strategies which are used to mitigate the impacts of urbanization by reducing runoff at the source and restore the natural hydrologic flow regime. Rainwater harvesting systems, permeable pavements, and green roofs are common LID techniques used to mitigate runoff generated from rooftops and parking lots. As the effectiveness of a LID strategy is determined by both the infiltration capabilities of alternative technologies and their placement within the watershed, this study optimizes the allocation of LID in a watershed to minimize the impact on the natural hydrologic flow regime, subject to an allowable cost. The hydrologic impacts of LID strategies are simulated using hydrologic and hydraulic models and are evaluated based on the peak flow. A genetic algorithm is coupled with the simulation models and applied for an illustrative watershed, located on the Texas A&M University campus, to identify the tradeoff between hydrologic impacts and implement costs of LID strategies.