Optimization of Stormwater Management Practices Under Increasing Urbanization and Climate Change in the US Mid-Atlantic Region

With conversion of land to urban areas, an increase in imperviousness creates water quantity and quality related problems such as water yield, sediment transport, nutrient retention, moderation of climate, and runoff mitigation. Anticipated changes in climate and urbanization are likely to increase the frequency of more common storm events (such as 2-year events), and puts a larger emphasis on effective mitigation measures. In an urban watershed, these drivers may cause more instances of flash flooding. A commonly-sought engineering goal is to reduce runoff flows to pre-development levels. To mitigate the impacts of flood events, best management practices 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. Flood mitigation includes conventional measures or so-called gray infrastructure (such as retention basins) and alternative low impact developments or green infrastructure (such as bio-retention, bio-swale, raingardens, and green roofs). In this study, the feasibility of retention basins and green infrastructure is assessed by proposing integrated Stormwater Management through ReTrofitting (iSMART). It involves ‘adaptive management’, which is basically the use of existing infrastructure before installation of new ones, optimal spatial placement, and cost-effectiveness of new infrastructure.

Green infrastructure seems to be more flexible and provides added benefits such as urban cooling, improved air quality, noise reduction, and aesthetics. The SUSTAIN model is used for spatial placement and cost effectiveness estimates. As a first step of adaptive management, the total runoff is retrofitted to existing infrastructure. Secondly, the remaining runoff, if still present, is then regulated with proposed new infrastructure along with its cost effectiveness. This includes setting suitable criteria of drainage area and slope, imperviousness, soil type, road buffer, and stream buffer for spatial placement of green infrastructure. Climate model simulations from CMIP5 are used for baseline (1981-2015) and future (2016-2035) periods to compute pre- and post-development flows due to climate change and urbanization. Urban development probability estimates are obtained from the SLEUTH model. Spatial placement of infrastructure is carried out at small watersheds (up to 1 square mile) across several counties of Maryland to obtain an optimal solution (feasible set) for each site. We hypothesize that green infrastructure offers economically sound, more flexible and less intrusive strategies than gray infrastructure.