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!

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