NSF CAREER recipient Ethan Yang exploring impact of green infrastructure on urban flooding

As a property owner, you may have more agency over the extent of flooding after a storm than you may think. 

Y.C. “Ethan” Yang, an assistant professor of civil and environmental engineering in Lehigh University’s P.C. Rossin College of Engineering and Applied Science, recently received a Faculty Early Career Development Program (CAREER) award from the National Science Foundation. His proposal focuses, in part, on the attitudes and behaviors of homeowners that can help reduce flooding in the Township of Bethlehem in Pennsylvania’s Northampton County. 

Urban areas used to rely on centralized combined sewer and stormwater, or CSS, systems. Domestic sewage, industrial wastewater, and rainwater runoff would funnel through a single pipe system to a treatment plant before getting discharged into a body of water. Heavy storms, however, often overwhelmed the system, and untreated water would overflow directly into waterways causing widespread pollution. 

The majority of these systems were converted in the 1990s to decentralized municipal separate stormwater sewer systems (MS4). This approach includes a variety of containment measures that keep rainfall from flooding urban areas, two of which can be owned and maintained by homeowners: rain gardens (an area with native vegetation and porous soil that captures rain and allows it to slowly infiltrate the soil) and rain barrels (units that connect to gutters and store water for later use on lawns and plants). 

“Rain gardens and rain barrels are considered green infrastructure because they’re cost-effective and sustainable,” says Yang. “However, when they’re used on a citywide scale, they create several challenges for a place like Bethlehem. First, the city should, at least in theory, test each individual element to understand how much water is being absorbed or released by the gardens, or how much volume the barrels are retaining. But at this scale, that’s not possible. Second, the city doesn’t have the manpower or budget to ensure this green infrastructure is maintained, that gardens are free from debris that can reduce their ability to absorb water, or the barrels have been emptied. And, in part because of these two challenges, the city can’t quantify the effect rain gardens and rain barrels will have during any given storm.” 

With his CAREER award, Yang will address this three-pronged challenge by creating a novel “human-cyberinfrastructure framework.” It will consist of two approaches: an Internet of Things-based green infrastructure network combined with agent-based modeling that will advance the understanding of decentralized sustainable stormwater management. 

The prestigious NSF CAREER Program awards grants annually in support of junior faculty members across the U.S. who exemplify the role of teacher-scholars through outstanding research, excellent education, and the integration of education and research. Each award provides stable support at the level of approximately $500,000 for a five-year period.

To solve the monitoring problem, solar-powered sensors will measure soil moisture beneath rain gardens and water level in rain barrels at locations across Bethlehem Township. The sensors will send real-time data to a web platform, from which the city will determine how well (or not) the infrastructure is functioning per its design criteria. 

Currently, homeowners who own a rain garden or barrel are obligated by law to ensure its functionality, and must fill out a handwritten form regarding their maintenance activity. “It’s very inconvenient,” says Yang. For Yang’s research, property owners will use smart home devices like Google Home or Amazon Alexa. Every time they clear their gardens of debris or use the water in their rain barrel, they’ll simply have to say something like, “Hey Google, I did my maintenance today.” This will feed data into the web platform that records both the timing and frequency of upkeep.

“If we can measure the frequency of different people doing this action in different locations, maybe we can figure out a way to incentivize those who live in a hotspot (an area prone to flooding) to do more of it if necessary,” says Yang.

To better quantify the effect of this green infrastructure, Yang will build a model that simulates both the natural process of how rainfall flows and the location of potential flood zones within the township, as well as property owners’ behavior. The model will quantify the effects on potential flood mitigation under various scenarios of green infrastructure installation, maintenance, and climate.

“So say a storm is supposed to hit in three days,” he says. “We’ll run the model, and we’ll be able to tell which areas are most prone to flooding, and the township can send out a warning to local communities along the lines of hey, make sure your rain barrel is empty or your garden is clean. This is the novel part of the research. The traditional modeling for stormwater management does not include this human element. By combining both the natural and human systems, we’ll have a better understanding of how this decentralized system works as a whole.”

Yang hopes to have a working prototype within five years, one that he envisions will assist with both emergency response measures and long-term urban planning to enable safer communities.

“I’ve always been interested in the interface between humans and the environment,” says Yang. My long-term goal is to enable as many people as possible to live more happily on this earth.”

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About Y.C. “Ethan” Yang

Yang’s research interests include water resources management, water-energy-food nexus, agent-based modeling, coupled natural and human complex systems, climate change risk assessment, international rivers, transboundary water policy, hydro-ecology, and urban stormwater management.

Yang has extensive experience in water management in the Great Himalayan and Sub-Saharan Africa regions and the Western U.S. He leads more than 12 research projects (more than $3 million) funded by the U.S. Department of Energy, National Science Foundation, the Work Bank, the International Food Policy Research Institute, the Consultative Group on International Agricultural Research and the Research Triangle Institute. Most of these projects evaluated climate change risk and social development influence on the water-energy-food-environment nexus for large river basins such as the Colorado, Columbia, Brahmaputra, Indus, Ayeyarwady, Mekong, Amu Darya, Yellow, and Niger. Along with the system modeling skill, Yang’s research can answer difficult questions of uncertain climate change impact and anthropogenic influence on water-energy-food-environment nexus quantitatively.

Prior to joining Lehigh’s faculty, Yang was a research assistant professor at the University of Massachusetts, Amherst. He is an author and co-author of 40 peer-reviewed journal papers and 35 conference papers. Yang received the NSF CAREER Award in 2020. He is a regular reviewer for top-ranking journals in water resources management and serves as an associate editor for the Journal of Water Resources Planning and Management (ASCE). He is also the Chair of the Water and Society Task Committee in the American Geographical Union. Yang is affiliated with Lehigh’s Institute for Cyber Physical Infrastructure and Energy (I-CPIE) and Institute for Data, Intelligent Systems, and Computation (I-DISC)

Related Links:

• Rossin College Faculty Profile: Y.C. Ethan Yang
• NSF Award Abstract: “CAREER: Understanding sustainable stormwater management via an Internet of Things-based green infrastructure…”
• Lehigh University: Complex Adaptive Water Systems (CAWS) research group
• Resolve magazine (Fall 2018): A Few Good Collaborators