As they approach and recede from a beach, waves move water along the shoreline. But the phenomenon, called longshore drift, also drags sediment and eats away at beaches over time. It’s a challenge for countries worldwide; for instance, the Netherlands has constructed a massive “sand motor” to mitigate shoreline loss caused by longshore drift.
Nimish Pujara
“More locally in Wisconsin, some beaches have revetments built in,” says Nimish Pujara. “Because of longshore drift, sediment can scour around these defenses and cause problems downstream because someone built a protection jetty or some other sort of structure.”
Pujara, an assistant professor of civil and environmental engineering at the University of Wisconsin-Madison, says the mechanisms of longshore drift are not well understood. Now, he and colleagues from the University of Delaware, University of Puerto Rico and Queen’s University in Canada are seeking a good way to quantify its impacts. With funding from the National Science Foundation, the team is taking a deep dive into the wave mechanics that drive these processes.
“We don’t really understand why sediment moves in the way it does, or takes the trajectories that it follows or how fast it moves,” Pujara says. “This project is really to uncover these dynamics that are happening everywhere, from the Dutch coastline to Wisconsin’s coastline and lots of other places in between.”
The research team will work at a facility that’s being set up for the project at Queen’s University. It will feature a swimming-pool-sized tank that’s 25 meters along each side, with “beaches” made from gravel, concrete and sand mixtures. The tank will include paddles to create waves, along with velocity sensors, wave height scanners, overhead cameras, lidar sensors to track changes to the beach, and more. Researchers will also work with the SWASH and XBeach open source models throughout the project.
Through the work, Pujara hopes to deepen understanding of how much sand moves along the shore due to coastal currents. Such knowledge could impact an array of coastal engineering and management areas, from improving green infrastructure efforts that employ natural barriers to protect the shore to dredging sand from the seafloor to replenish eroded beaches.
“A lot of beaches march, or move along the shore, and that’s how they lose sand,” Pujara says. “Dealing with this is one of the main tasks for the Army Corps of Engineers, and dredging companies that move sand toward the shore make up a huge industry. Anything we can do to help understand the rate at which you need to nourish—and why you need to nourish—these beaches will help more effectively manage those resources.”