Date of Award
Summer 7-15-2025
Document Type
Dissertation - Restricted
Degree Name
Doctor of Philosophy (PhD)
Department
Civil, Construction, and Environmental Engineering
First Advisor
Walter McDonald
Second Advisor
Anthony Parolari
Third Advisor
Brooke Mayer
Abstract
Urban stormwater runoff contributes to flooding and surface water pollution, issues exacerbated by aging infrastructure, changing climates, and urbanization. Green stormwater infrastructure (GSI) can help address these challenges by capturing and treating runoff near its source. However, its benefits are limited by unclear performance under unique conditions, ineffective treatment of specific pollutants, and uncertain variability of design criteria. This dissertation addresses these challenges through four objectives. First, it evaluates an interconnected rock swale and bioretention system treating runoff from an elevated highway interchange, which is a unique setting that generates runoff with high energy and pollutant concentrations. Results showed that total suspended solids and total phosphorus concentrations in highway runoff are orders of magnitude greater than other surfaces, yet rock swales and bioretention in series effectively reduced concentrations and pollutant loads. Second, runoff from highways may contribute to thermal pollution of urban waters, and it is unclear how specific treatment steps implemented to manage highway runoff, particularly rock swales, mitigate or exacerbate stormwater temperatures. Findings revealed that rock swales warmed runoff to a greater degree than highway decks, while sequencing bioretention downstream reduced temperatures below thresholds for cold-water species like trout. Third, while bioretention effectively treats many pollutants, it often increases reactive phosphorus concentrations, which can harm downstream ecosystems. To address this, an end-of-pipe filter containing activated alumina and iron filings was developed and installed at two bioretention systems. After several months, the filters reduced the mean concentrations of reactive phosphorus by 39-49%. Finally, states and localities prescribe GSI design guidelines; however, it is unclear how design criteria vary or why. To address this, data was compiled from 62 GSI design guidelines across the U.S., and significant variations were found in design elements such as slope, soil, and geometry, much of which correlated with factors (e.g., longitude, annual rainfall volume, and topography) that follow an east to west trend. Overall, this dissertation helps advance GSI by demonstrating how welldesigned systems of interconnected GSI treat highway overpass runoff and influence runoff temperatures, proposing an approach to reduce reactive phosphorus concentrations through underdrain filters, and revealing underlying reasons for GSI design variability.