Research at the Ohio State University aims to keep stormwater sediment stranded on the road.
By Zach Mortice
When Halina Steiner tested new sediment-collecting infrastructure in her lab at the Ohio State University (OSU), she noticed a mysterious magnetism pulling people toward the bits of beveled foamboard she had crafted into sediment collectors. As water mixes with dirt and sand starts flowing across the planks of foam, and sediment settles into intricately carved CNC-milled grooves, “it’s very mesmerizing,” Steiner says. It’s like sending a paper boat down a stream or, more accurately, “down the gutter,” she says, because that’s the exact place Steiner is looking to intercept sediment that pollutes and clogs waterways.
Steiner, an assistant professor of landscape architecture, has completed initial proof-of-concept tests on the project, called Curbing Sediment, with her co-researcher Ryan Winston, an assistant professor of engineering. She’s also joined by Alec Grimm, currently a graduate student in the Department of Food, Agricultural, and Biological Engineering, and Avee Oabel, an undergraduate landscape architecture student.
The team simulates how stormwater travels across streets and concrete curbs. Each trial involves running sediment-laden water over sections of foam board with quarter-inch-deep grooves carved into them, which become troughs that collect sediment. The OSU team has tested 20 geometries of groove troughs, and early results indicate that this method can pull at least 80 percent of sediment from water. Along roadways, this sediment is often combined with toxins and metals such as copper, zinc, cadmium, and grease before infiltrating sewer systems.
This type of decentralized stormwater infrastructure, which isolates pollutants close to their source, is often less expensive and easier to install than traditional infrastructure such as larger sewer tunnels and advanced treatment plants that cost many millions. And if these sorts of interventions don’t divert excess sediment, the only other remedy is dredging out major waterways where the sediment ends up, which is also very costly. (The U.S. Army Corp of Engineers will spend $85 million this year alone on dredging a section of the Mississippi River from Baton Rouge, Louisiana, to the Gulf of Mexico.)
“We talk a lot about the effluent that’s going into the water, but we don’t talk that much about the sediment, and I think it’s because it’s a lot harder for us to understand exactly what it is,” Steiner says. “It’s microscopic, and it’s also something that, when it gets into the waterways, is really hard to remove.”
Steiner had originally intended to simulate the dynamics of sediment-laden water with computers, but the computing power needed would have been too expensive and impractical to obtain. Instead, they started with something a bit more down to earth. “We started looking at tactile paving, which is for visually impaired people, because we know that is something that’s already in the public right-of-way,” Steiner says.
From there it was an iterative process of testing different geometries along curbs and aprons. Each trial weighted water before and after it was run through each scenario, weighing the sediment separately. Turbidity sensors at inflow and outflow points also measured the amount of sediment in the water.
For the curb sections, the OSU team researched collection troughs in the shape of triangles, dimpled patterns, and squares, which were the most effective. In the apron sections, they tried lines (similar to highway rumble strips), zigzag patterns, and dots, which Steiner called “effective and playful.”
“It was very much a process of building on what we were observing from the previous tests, because there are really infinite options,” she says.
This leaves open the possibility for sediment collection that can be designed, and that’s an important thing for infrastructure as ubiquitous as curbs and streets. “I think they can be quite beautiful,” Steiner says. While patterns of perpendicular lines mostly resemble rumble strips, squiggly zigzags offer a hint of spontaneity and whimsy. Beyond raw function, street-side sediment reservoirs can make stormwater and sediment management a more explicable process, giving people a way in to this often hidden realm of urban ecology.
Steiner and her team are looking to field-test a prototype on campus, and they envision the sediment being sucked up with street sweepers fitted with vacuum attachments, similar to what New Orleans uses to suck up Mardi Gras beads when revelry subsides. She also wants to determine what the potential physical footprint of such a system might be. But, Steiner says, “It’s a little hard to find out how many miles of curbs there are.”