Date of Award

Spring 2022

Document Type


Degree Name

Master of Science (MS)


Civil, Construction, and Environmental Engineering

First Advisor

McDonald, Walter

Second Advisor

Parolari, Anthony

Third Advisor

Mayer, Brooke


Managing stormwater is a crucial task for many communities that are required to mitigate the harmful effects of pollution from urban runoff. Subsurface gravel wetlands are an emerging type of green infrastructure that can be used to manage stormwater through the capture and slow release of runoff. These wetland systems are unique to other types of green infrastructure in that they have a distinct fully saturated gravel layer below an occasionally saturated soil layer. While there is substantial literature on the performance of different types of green infrastructure, such as bioretention, bioswales, and permeable pavements, there is a lack of monitoring studies on the performance of subsurface gravel wetlands. To fill this gap, the flow and water quality in a subsurface gravel wetland in Oshkosh, Wisconsin were monitored. To do so, the influent and effluent flow rates were captured, and water quality samples were collected at the influent, effluent, and an observation well and tested for total suspended solids, total nitrogen, total phosphorus, chloride, and E. coli. Nine storm events were captured over the summer of 2021 and results indicated that the wetland had a median volume reduction of 73.7% and a median peak flow reduction of 89%. The average and median total suspended solids concentration reduced by the wetland was 49% and 37.5%. Total nitrogen and total phosphorus concentrations increased on average by 20.8% and 0.22%, respectively. However, these results were influenced by several influent concentrations that were below the concentration levels that are generally irreducible by green infrastructure. In cases where influent concentrations were above irreducible levels, total phosphorus reduction was 45.3% (influent ≥ 0.25 mg/L) and total nitrogen reduction was 38% (influent ≥ 2.5 mg/L). Results for E. coli were inconclusive due to minimal quantifiable results. Chloride concentrations in the inlet and outlet decreased over time, indicating the salt from winter was flushed from the system in late spring and early summer. Overall, this study shows that the subsurface gravel wetland generally performed similarly to other types of green infrastructure and could be a good management practice to mitigate the harmful effects of stormwater runoff.

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