COLLEGE PARK, Md. -- A new University of Maryland study shows small decentralized stormwater management practices such as rain gardens can make a significant impact on a watershed’s resiliency.
In a new case study published in the Journal of Water Resources Planning and Management, researchers in UMD’s College of Agriculture and Natural Resources used predictive modeling to examine two distinct watersheds. They show that by managing stormwater with green infrastructure a watershed can absorb more of the increased rainfall associated with climate change than can more traditionally designed large stormwater basins. However, they also found that both green and traditional stormwater systems failed to fully handle the amount of rain resulting from larger or more intense rain events.
“What we design now is in place for 20 or 30 years, so we should design it with future climate conditions in mind as opposed to what the past rain has looked like,” explains lead researcher Mitchell Pavao-Zuckerman, assistant professor in Environmental Science & Technology.
Pavao-Zuckerman and graduate student Emma Giese used a USDA soil and water assessment tool together with past daily streamflow data from United States Geological Survey (USGS) to predictively assess the performance of two watersheds in Clarksburg, Maryland, a growing suburban town in Montgomery County. The two watersheds have a distinct development history - one has several larger-scale detention ponds or stormwater basins for a more traditional approach to stormwater management, while the other has a heavy presence of smaller-scale green infrastructure like rain gardens, dry detention ponds, and sand filters. Both watersheds were monitored before and after development to see the impacts of green infrastructure, and both are near a weather monitoring station with climate data that is readily accessible.
“Green infrastructure consists of things with a much smaller footprint than a stormwater basin, but there are more of them in the watershed, so it comes down to measuring the aggregated effect of a lot of small things in one watershed rather than one or two large things in another watershed,” says Pavao-Zuckerman. “Partnering with the USGS to have a good data source at the watershed scale and finding the right model for the question was key.”
To model future climate change scenarios for these two watersheds, Pavao-Zuckerman and Giese enlisted the help of Adel Shirmohammadi, professor and associate dean in the College of Agriculture & Natural Resources. “Together, we were able to use the USGS data to train the [USDA] Soil and Water Assessment Tool or SWAT model, taking into account the geography of the watersheds, slope, soil type, impervious surface, built versus open space, and other parameters to determine how much rainfall actually becomes runoff or flooding risk,” says Pavao-Zuckerman.
Using this model, the researchers were then able to take climate change projection data for increased storm frequency and rainfall to run a variety of future scenarios and see how these different watersheds would manage. “We’ve already seen a significant increase in rainfall in the present day, so we were surprised to see that our baseline present day measure was already seeing the effects of increased rain,” says Pavao-Zuckerman.
They found in climate change scenarios that on most rain days the watershed with rain gardens and other types of green stormwater infrastructure absorbed more water and had less runoff than the traditional management watershed with larger stormwater basins. However, in these scenarios both systems failed to handle the high amounts of rain produced by larger, more intense storms.
“We are seeing more large storm events so either of the systems are overwhelmed or are still saturated by the time the next storm event comes,” says Pavao-Zuckerman. “So it is really the bigger rain events where we are seeing things not work as well, and that’s concerning partly because we know that with climate change these more intense events are going to become more common. This points to the need to plan for these more intense weather events in stormwater management infrastructure.”
The modeling showed that increasing capacity for some existing systems or increasing the presence of green infrastructure in the watersheds made them more resilient to future extreme rain events. With that in mind, Pavao-Zuckerman and Giese worked with Amanda Rockler, watershed restoration specialist and senior agent with UMD Extension and the Maryland Sea Grant Program, to provide insight into what was feasible to implement. “Our work allows us to see what the added return on investment in these different climate and stormwater management scenarios might be,” says Pavao-Zuckerman.
“Assessing Watershed-Scale Stormwater Green Infrastructure Response to Climate Change in Clarksburg, Maryland” by Mitchell A. Pavao-Zuckerman (corresponding author), Emma Giese, Amanda Rockler, and Adel Shirmohammadi. ORCID: https://orcid.org/0000-0002-9657-2892. Email: firstname.lastname@example.org. This paper is available through the Journal of Water Resources Planning and Management, DOI: 10.1061/9780784479018, or through Pavao-Zuckerman’s Ecolody Lab website.