Making the shift from grey to green infrastructure for stormwater management: a case study of austin, texas

Abstract

Austin, Texas is the eleventh most populous city in the United States as of July 2019, and the population is swiftly growing (U.S. Census Bureau, 2020). Increasing urbanization inadvertently leads to pollutant deposition and build-up that is consequently washed-off with stormwater runoff into the receiving waters (Goonetilleke & Lampard, 2019). The culmination of this changing land use is a higher likelihood of flooding, severe stream-bank erosion, and degraded water quality throughout the city's watersheds. Therefore, I evaluated whether shifting away from a traditional stormwater management approach towards a green infrastructure strategy would be beneficial to Austin. I focused on the Slaughter Creek Watershed within the city. To model pollutant concentrations in runoff, I evaluated historical daily precipitation data for a 51-year period from a station in central Austin was evaluated to calculate the average precipitation value of the two-year storm. Twenty years of water quality data for untreated stormwater were acquired from a monitoring location in central Austin and paired with the precipitation values. Regression analysis was used to determine a relationship between measured precipitation and the concentration of each of four pollutants: total suspended solids, total nitrogen, total phosphorus, and E. coli, in stormwater runoff. The pollutant removal efficacy of two traditional stormwater management features, underground detention vaults and sand filters, and two green infrastructure features, bioretention and permeable pavers, was evaluated against the calculated pollutant concentrations. The EPA-funded Community-enabled Lifecycle Analysis of Stormwater Infrastructure Costs tool was used to determine implementation costs and cobenefits of three stormwater management scenarios in the Slaughter Creek Watershed. The results of the model indicate that a hybrid approach, combining both green and traditional infrastructure features, is the most inexpensive and captures the most runoff by volume. However, the green infrastructure approach has significantly more co-benefits and has greater positive water quality impacts. The traditional infrastructure scenario was the most expensive, had the fewest co-benefits and water quality impacts, and captured the least runoff volume. The information in this study indicates that the Slaughter Creek Watershed will benefit from a revised hybrid approach featuring primarily green infrastructure practices yet incorporating traditional features where more practicable.