In urban areas, stormwater runoff is a result of paving over and building on permeable surfaces. Stormwater runoff is a simple concept to understand, but it is also a process with big impacts on the environment. Stormwater runoff is a problem because it picks up soil, chemicals, and other pollutants before flowing into our sewer systems, or directly into lakes, streams, and wetlands.

In his recently completed master's thesis, geography graduate student Patrick Strong (supervisor Dr. Paul Hudak) looked into ways to reduce water pollution from urban stormwater runoff. He examined the effectiveness of rain gardens to protect against nitrogen rich overflow events from places like wastewater treatment plants. While nitrogen is a nutrient that plants need to grow, it also flows off the land and into our waterways, causing eutrophication, habitat degradation, and losses of biodiversity.

Patrick looked at rain gardens - shallow infilled depressions designed to treat urban stormwater (Photo 1). These features are highly vegetated and help improve stormwater quality through a suite of processes, including mechanical filtration, sorption, ion exchange, biological uptake, ammonification, nitrification, and denitrification. A series of simulated flood events (photo 2) showed that rain gardens are able to effectively intercept extremely high levels of nitrogen. Eventually, however, this nitrogen flushed out of the system over an extended period, potentially leading to degraded waterways. This means that while rain gardens are effective in reducing water pollution, they must be remediated to prevent chronic nutrient outputs of nutrients over the long term.

This research added to the growing body of evidence pointing towards rain gardens as effective low impact developments to treat urban stormwater runoff.

Photo 1: The Denton City rain garden at the Waste Water Treatment Plant where Patrick Strong conducted his research.

Photo 2: Photo of a flood event in progress.