Building a River in the Lab

A $125,000 grant is helping Tulane researchers investigate how floods cause meandering rivers to abandon their bends and carve new paths.

Inside a Tulane laboratory, a river winds through a broad basin filled with sand. Its water and sediment are delivered through a computer-controlled system, while cameras record the river’s movement and a lidar instrument maps subtle changes in the surrounding topography.

The river is small enough to cross in a few steps, but the process unfolding within it occurs across some of the world’s largest waterways.

Tulane University Earth and Environmental Sciences professor Kyle Straub and his research group are studying how chute cutoffs develop in meandering rivers. These cutoffs occur when floodwater spills across the land separating two sections of a river bend, carves a new channel, and creates a shorter, straighter route for the river.

The American Chemical Society awarded Straub a $125,000, two-year Petroleum Research Fund grant to investigate the mechanics governing that process. Straub was among 80 researchers selected for grants through the fund’s spring 2025 application cycle.

Although chute cutoffs are common in meandering rivers around the world, researchers still lack a mechanistic model capable of predicting when and where they will occur. Straub and his collaborators believe the answer may depend on the interaction between the shape of a river bend and the magnitude and duration of flooding.

“We’re studying specifically how curvy the channel is when you develop these chute channels,” Straub said. “Lower-sinuosity bends, we think, are more optimal for developing chutes.”

The research team hypothesizes that a chute cutoff develops when a river enters a critical window in its geometry and then experiences enough overbank flow to excavate a new channel. Their project will combine controlled laboratory experiments, a global dataset of river cutoffs, field observations from four rivers and the development of a numerical model.

The work began with research led by Chenliang “Chen” Wu, then a postdoctoral researcher in Straub’s group. Wu used time-lapse satellite imagery to examine river systems around the world, studying how channels changed and the conditions present when chute cutoffs formed. Wu, who co-wrote the grant proposal with Straub, has since moved to a faculty position at the University of Bergen. He and Straub will continue collaborating and will co-advise the graduate student who takes on the project’s next phases.

Before that broader work moves into the field and numerical modeling, the research group began testing its ideas on a smaller scale in the laboratory.

During summer 2026, the project gave Earth science undergraduate Asher Josephson an opportunity to explore those questions in the laboratory. Asked what attracted him to river science, Josephson offered a refreshingly direct answer.

“I like water,” he said. “I think it’s cool. I think it’s important.”

Josephson, who is also pursuing a minor in River-Coastal Science and Engineering, helped construct and operate the experimental river with guidance from Straub and doctoral student Oluwadamilare “Dare” Odugbesan. He contributed to nearly every part of preparing the basin.

“I did most of the putting the sand in the basin, mixing the mortar and carving the channel,” Josephson said. “I did a lot.”

Mortar was mixed into the sand near the entrance to prevent erosion caused by the experimental infrastructure from influencing the results. Elsewhere, the surface had to be carefully smoothed and the channel precisely carved. Odugbesan trained Josephson on the equipment and helped him set up and run the experiments, including the system used to control the flow of water and sediment entering the basin.

Once an experiment begins, the river runs at its normal, or base, flow before the researchers initiate a simulated flood. Pulses of dye make the water’s movement visible, cameras capture the channel’s development, and lidar surveys produce detailed elevation maps showing where sediment has eroded or accumulated.

Even in a carefully controlled laboratory, the river does not always behave as expected. During one early run, the team discovered that the developing chute was moving in the wrong direction. The elevation data helped reveal where the surrounding surface needed to be raised before the next attempt.

That trial and error is an essential part of the experience for Josephson.

“That’s just what it is, right?” he said. “I like the trial and error.”

Straub’s group plans to repeat the experiment using channels with different degrees of sinuosity, a measure of how much a river curves. The researchers expect the initial channel geometry to favor the formation of a chute cutoff. They will then carve a more sinuous channel, subject it to the same flooding conditions and determine whether a cutoff still develops.

By comparing repeated experiments and studying changes in the topographic maps, the team can identify where erosion begins and track how an emerging chute grows. Those controlled results will help the researchers test the patterns Wu identified through satellite observations.

“If we can nail down in the lab that the observational data we have in the field can also be reproduced under very controlled conditions, we’ll have a better feel for whether our theory is working,” Straub said.

Understanding river cutoffs has implications extending far beyond the laboratory. As rivers migrate and carve new paths, they reshape floodplains, influence vegetation and aquatic ecosystems, and move sediment through the landscape. Channel movement can also release contaminants stored in floodplain soils or shallow groundwater, affecting pollutant transport and potentially exposing downstream communities and ecosystems.

The findings could also help guide river restoration and other nature-based approaches intended to restore some of the functions lost when rivers are heavily engineered.

“We want to know how to better manage river systems and understand how they function if they have not been heavily engineered,” Straub said. “We’re trying to do a lot of nature-based solutions that bring systems back toward their natural form, but we need to understand how they naturally function.”

The project also addresses questions about the sedimentary record left behind by ancient rivers. Chute cutoffs influence the arrangement of channel sands and barriers within river deposits, which can affect the movement of fluids through sedimentary rock and the quality of associated hydrocarbon reservoirs. That connection makes the research especially relevant to the mission of the ACS Petroleum Research Fund.

For Josephson, the summer project offered more than an introduction to river science. By helping construct the channel, operate the equipment, interpret elevation maps and adjust the experiment when it did not behave as expected, he became part of the process of turning a scientific theory into testable evidence.

That persistence will remain essential as the project expands from the laboratory to field research and numerical modeling. By recreating the forces that reshape rivers, Straub’s team is working toward a better understanding of when waterways will carve new paths and what those changes could mean for landscapes, ecosystems and communities around the world.