Optimization of Stormwater management practices under Climate Change and continued Urbanization in the US Mid-Atlantic region

Stormwater mitigation practices include use of gray (such as retention basins) and green (also known as low impact developments such as bio-retention, bio-swale, raingardens, and green roofs) infrastructures. Anticipated changes in climate may increase the frequency of more common storm events (such as 2-year events). In addition to climate change, continued urbanization will cause more instances of flash flooding due to increased imperviousness and reduced infiltration. In an urban watershed, these drivers may affect proper functioning of ecosystem services by altering nutrient transport, soil erosion, sedimentation, and channel incision. A commonly-sought engineering goal is to reduce runoff flows to pre-development levels. To mitigate the impact of flood events, best management practices (BMPs) are employed to regulate post-development flows. These practices vary from one region to another with municipalities often weighing the relative magnitudes of stormwater infrastructure costs and maintenance with benefits of stormwater mitigation. In this study, the feasibility of retention basins and low impact development (LID) infrastructure is compared using optimization through a linear programming approach for projected potential 2-, 5-, and 10-year storm events given climate change scenarios and associated change in weather patterns.

BMPs used in this study are 1) retention basins, 2) LID, and 3) a 'flex' approach (use of both retention basins and LID). These are applied to small watersheds (up to 1 square miles) across several counties of Maryland to obtain an optimal solution (feasible set) for each site. We hypothesize that use of LID provides a superior solution compared to gray infrastructure to cope with future storm events with increased flood risk under climate change. Climate model simulations from CMIP5 are used for baseline (1985-2014) and future (2015-2040) periods to compute pre- and post-development flows due to climate change and urbanization. Urban development probability estimates are obtained from the SLEUTH model. Runoff capture is assessed using gray and LID infrastructures for the 2-, 5-, and 10-year storm events. Balancing of stormwater management cost and of subsequent benefits are then calculated using an optimization approach.