Three Questions for Elizabeth Fassman-Beck

It’s been an exciting summer for Elizabeth Fassman-Beck, associate professor in the Department of Civil, Environmental and Ocean Engineering at Stevens Institute of Technology. Fassman-Beck, a leading expert on green roofs and co-author of Living Roofs in Integrated Urban Water Systems, is overseeing the construction of a Living Laboratory for green infrastructure (GI) research.

The laboratory features differing designs for bioretention planters, green roofs and rain gardens, which will offer unique opportunities for data collection and side-by-side comparison. By the end of fall 2017, there will be three complete rain gardens on the Stevens campus (see pictures of the construction in progress in this PowerPoint presentation).

Each of the green infrastructure installations is configured to allow detailed quantitative research on performance, which will contribute to future improvements in green infrastructure modeling. The Living Laboratory will also create opportunities for K-12 STEM curriculum development in partnership with the Stevens Center for Innovation in Engineering Science Education.

We asked Fassman-Beck to talk about her methods and goals for the laboratory.

JWW: How will you collect performance data on planters, green roofs, and rain gardens?

EFB: Every site and each GI technology has unique performance objectives. For some applications, water quality improvement may be the primary stormwater management goal. In other locations, controlling runoff hydrology (flow rate and/or volume) might be the main concern, especially where combined sewer overflows are an issue. In many locations, all of these are desired outcomes.

At the moment, we have different performance questions for each of the GI technologies within the Stevens Living Laboratory.

• Bioretention planters: Detention (delaying and mitigating peak discharge) is number one. We’re also interested in retention (reducing total volume of discharge), which we think might differ among individual planters because we’ve used two different configurations of engineered media. To measure detention and retention for each individual planter, we have sensors to measure inflow from the rooftop and outflow through an underdrain. We also have an array of soil moisture sensors in each planter to track how the water flows through the system. This is all being done in partnership with the EPA’s Office of Research and Development in Edison.
• Green roofs: Characterizing water quality and quantifying stormwater retention are the research goals. With respect to water quality, the incoming rainfall is “clean,” but there is some concern that nutrients may discharge from green roofs at high concentrations. We will capture all of the runoff from 20 different configurations of green roof media that we’ve designed, and analyze it for nitrogen and phosphorus content. The overall objective is to try to link chemical and physical composition of engineered media to nutrient leaching potential. Ideally, we’ll identify materials that prevent or minimize nutrient leaching, but maintain a lightweight growing media with high water holding capacity.
• Rain gardens: Retention and detention will be quantified through a combination of sensors to measure flow into and out of each rain garden, and soil moisture sensors distributed throughout the engineered media. We also have the potential to sample for water quality performance using automatic samplers, but this is very resource-intensive.

In all cases, the continued ability to collect data depends on grant funding. While we’ve been able to build and instrument all of these systems, we’re looking for partners to enable long term data collection!

JWW: What are some of the challenges in acquiring quantitative data on green infrastructure performance, and how does this project address them?

EFB: One of the most exciting aspects of the Stevens Living Laboratory was working together with Stevens Facilities Management and our external consultants from the beginning, to ensure that the logistics of the design enabled research. Safe, physical access for researchers is the number one concern. The locations and numbers of inlets and outlets for any stormwater control measure (also known as a best management practice) affects the amount of instrumentation needed, and the ability to measure flow accurately or collect samples for water quality analysis. All of these considerations went into the design of the Living Laboratory, without compromising system functions or aesthetics.

A fun challenge for my summer research students has been developing two unique systems for measuring accurately a wide range of flows from the roof downspouts, which is the inflow to the bioretention planters. Beginning with a system developed along with my previous research on green roofs at the University of Auckland (New Zealand, where I was a professor before joining Stevens) that’s called an “orifice-restricted device” (ORD), we’ve modified the design to account for the particular configuration of the North Building’s downspouts.  We are going to compare the new ORDs under field conditions over the next few months.

Another major challenge for measuring GI performance arises simply because it never rains the same way twice. To “prove” performance, the Living Laboratory was designed to duplicate experiments in the same rainstorm. For the bioretention planters and the green roof systems, each unique design combination is present in two physically identical systems. For rain gardens, by the end of the year, there will be three separate rain gardens on campus that share specific design aspects in pairs. Ultimately, for each of the GI technologies, we’re able to test lots of different design combinations at the same time, subject to the same rainfall. This sort of direct, side-by-side performance comparison configuration at field scale is unique.

JWW: How do you hope this will influence the future of green infrastructure design?

EFB: We aim to establish long-term performance data sets with statistically verifiable results. Most GI technologies are living systems. Their performance may change with time – we want to take a long view. On a practical level, the detailed types of data we are hoping to collect will help the stormwater industry (regulators and practitioners) understand how design choices such as engineered media composition and inlet and outlet configurations affect stormwater management outcomes. We will also use these data to refine engineering models. At the moment, available models for GI are very coarse, and their accuracy for predicting flow rates and volumes has not been proven. The data needed to calibrate and verify models is really limited – we’ve designed our research approach to generate the data that’s needed. We also aim to train the next generation. Beyond integrating research into teaching at Stevens, we intend to develop K-12 STEM curricula around GI for integration into New Jersey schools. We have the expertise for the field work, the modeling, and the educational development. We’re really looking forward to the future!