Analyzing the Long-Term Performance of a Constructed Stormwater Wetland and Investigating Potential Techniques to Increase Performance

Abstract

The impacts of stormwater runoff have been a growing concern due to an increase of urbanization, a practice that results in eliminating or reducing pervious areas that are capable of infiltration. The reduced pervious land leads to an increase of stormwater runoff. Stormwater runoff can be detrimental because of the quantity and quality impacts in downstream waterways, such as flooded land and degraded water quality. One method to mitigate stormwater runoff effects is the use of green stormwater infrastructure, which can reduce the quantity of stormwater runoff on downstream systems and improve the effluent water quality. One type of green stormwater infrastructure is a constructed stormwater wetland.

Villanova University has a constructed stormwater wetland that was reconstructed in 2011, called CSW 2.0. Since its reconstruction, the system has been monitored for water quantity and quality benefits. A primary goal of this present research was to understand how time played a role in the performance of the CSW 2.0. Performance for this work focused on the comparison of influent and effluent data from the CSW 2.0. Performance was analyzed from three perspectives: quantity, quality, and mass loading. The goal of this analysis was to understand if age of the wetland and seasonality influenced performance. Results from this work indicate that as the CSW 2.0 aged, performance mostly improved. In addition, results showed that seasonality played a role in performance.

A second goal of this research was to understand two different techniques that could be used to further improve the performance of the CSW 2.0. The first technique was a real-time control structure installed at the CSW 2.0 outlet that could control effluent flow. A comparison of historic rainfall events and rainfall events with an active real-time control showed the gate changed the shape of the hydrograph and properties of the peak flow for a given event. The second technique was assessing if the hyporheic zone could be used to remove additional contaminants from the water in the CSW 2.0. The hyporheic zone is the saturated soil where groundwater and surface water mix and allows for diverse microbes and redox properties. Hyporheic zone research has mostly focused on engineering streambeds to increase flow into the zone and enable treatment. Before any modifications can be made to the hyporheic zone in the CSW 2.0, preliminary data analysis was necessary. One component was to understand how flow currently moves through the hyporheic zone by using electric conductivity as a tracer. The second component was to determine the amount of soluble reactive phosphorus, a contaminant that could be removed in the hyporheic zone, present in the CSW 2.0. Results from this study indicated that hyporheic flow occurred in the CSW 2.0 and soluble reactive phosphorus was a major component of phosphorus for the CSW 2.0.