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How Green Rooftops May Solve The Stormwater Crisis In Hoboken

Thirty-eight green roof setups have been installed on a new campus building in New Jersey to determine the best method of bioretention for stormwater runoff. Researchers at the Stevens Institute of Technology in Hoboken will spend this fall studying 19 duplicated rooftop setups (38 in all) and analyzing data to figure out what works best for filtering pollutants and retaining water in a city plagued by the negative effects of stormwater runoff.

Bioretention is a huge issue for cities where soil and trees have been replaced with pavement.

Elizabeth Fassman-Beck works as an associate professor in the Department of Civil, Environmental and Ocean Engineering at Stevens Institute of Technology, where she teaches engineering hydrology and stormwater management. Fassman-Beck also happens to be an expert on green roofs; check out her book on living roofs here. The Living Laboratory research site is Fassman-Beck’s latest project, located on the new North building.   

In the lab, students are managing green roof setups, biorentention planters designed to filter rainwater, and a rain garden to explore different modes of dealing with stormwater runoff. Bioretention—the process of taking pollutants out of stormwater—is a huge issue for cities and towns like Hoboken where pavement is plentiful but soil, shrubs and trees are in low supply.

Mile Square City has a massive runoff problem. 

Hoboken sits smack-dab in the center of Hudson River’s floodplain, with the city’s lowest point just three feet above sea level. Hoboken’s proximity to Manhattan has made it akin to another New York City borough. But with seemingly constant growth, industry, and expansion, Hoboken lost most of its natural systems for dealing with water runoff; namely, trees, shrubs, and soil.

“When it rains, runoff goes into same sewer that holds waste,” Fassman-Beck said in a prepared release on the campus website. “The sewer pipe doesn’t have the capacity to carry all of it to the treatment plant, so some runoff flow bypasses the treatment plant and discharges untreated runoff directly into the Hudson River. When those water treatment systems were originally conceived, no one imagined there would be such a huge population build up as there is now.”

Fassman-Beck’s solution is, “putting small-scale water retention systems everywhere. We can’t take up a parking space to build a rain garden. Instead, we want to optimize bioretention planter design to have meaningful impact. We want to know how small is too small for one of these systems, and figure out the potential for widespread implementation here in Hoboken.”

The answer to stormwater runoff may be found well above ground level. 

The Living Laboratory’s bioretention planters, which hold a mixture of soil and sand, have soil sensors to determine how much water is caught by the medium. That data will educate the scientists—and by extension, city planners—to help figure out what kind of planting beds could benefit the city.

“The hypothesis for our research is that the aggregate type matters,” Fassman-Beck told Next City. “In other words, not all sands or rocks are created equal when it comes to influencing water movement.” She added that for places like Hoboken, rain gardens on ground level might not be the best way to deal with stormwater. Bioretention planters are better solutions, since they are mobile and catch water via spouts like gutters. But the best place to find answers, she says, may be at the tops of buildings.

There, plants can absorb water and prevent rainfall from flooding out streets and washing pollutants into waterways in the first place. To mitigate the fact that the eventual overflow will have high levels of nitrogen and phosphorous (from the dirt and plants), Fassman-Beck and her students are experimenting with different mediums to see what can leach nutrients so they don’t end up similarly damaging water bodies.

“The overall objective is to try to link chemical and physical composition of engineered media to nutrient leaching potential,” Fassman-Beck told the website Jersey Water Works. “Ideally, we’ll identify materials that prevent or minimize nutrient leaching, but maintain a lightweight growing media with high water-holding capacity.”

Lab results can educate other buildings, neighborhoods, and cities worldwide. 

Lab results are expected to pour in quickly, meaning planners throughout Hoboken—as well as in cities across the country and even world—could use the data to benefit other systems for buildings and neighborhoods.

Green roofs are initially expensive, but the other costs down the road of reversing pollution in waterways and restoring ecosystems are far greater. Cities are taking note: San Francisco last year became the first city in the United States to require green roofs on new developments. And as early as 2010, Toronto began implementing green-roof requirements. With work like the Living Laboratory underway, it’s likely only a matter of time before green roofs and bioretention planters are the norm, not the exception.  

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