Researchers Building a Toolbox to Analyze Dangerous Currents at Low-Head Dams

In any one year, 15-30 people drown at low-head dams in the U.S. In general, the public is unaware of the drowning potential of the rotating current, known as a reverse roller, immediately downstream and just beneath the surface. Individuals overturning in a kayak, trying to rescue a family pet, and even participating in carefully prepared training exercises by search and rescue have all been victims.

Although recreation is an important function of many rivers in the U.S., a lack of knowledge of low-head dams and the deadly reverse roller presents a very real risk for those who point their paddles downstream.

“If you’re recreating and you’re traveling downstream, it can be almost impossible to see the drop of the low head dam, so you’re basically on top of it when you see it,” said Professor Brian Crookston from the Utah Water Research Laboratory.

Crookston is developing a toolbox with Professor Rollin Hotchkiss at Brigham Young University to help those involved in public safety to analyze the risk of reverse rollers at low-head dams. The rotating current that traps people is a function of river discharge and stage. If the water elevation below the dam is high, like after a rainstorm, the reverse roller can form.

“People might go out kayaking on a Sunday and everything is safe,” Crookston said. “But then you might get a half inch of rain overnight and suddenly the reverse roller is there. People who are familiar with the dam may not know how quickly conditions can change and that there is a new danger.”

He hopes his safety assessment tools will help with risk assessments and public safety improvements.

The work began as a volunteer effort five years ago. No funding, no one asking for the data, just researchers and engineers at Utah State University, BYU, and other organizations passionate about the work. Thankfully professional organizations such as USSD, ASCE and ASDSO were supportive.

Through crowdsourcing efforts where individuals would spend time over their weekend scanning Google Earth and recreators using apps to geolocate and take pictures of low-head dams, a nationwide database was formed to identify all of these structures in the lower 48 states. Advanced tools were developed to automate this process, such as a recent master’s project at USU by Caitlin Arnold. This collaborative, crowdsourced effort became the foundation for Crookston to work with BYU and the Federal Emergency Management Agency to get the data needed to improve safety and public information at these dams.

To build a toolbox useful at any of these structures in the database, Crookston partnered with UWRL’s AggieAir to get LiDAR scans of topography by rivers, augmented by ADCP boat measurements to see what’s beneath the water surface at a low-head dam. The field data was used to create example models. Crookston said UAVs are a great way to scan the river and get the most accurate data needed for effective modeling so stakeholders can consider site-specific conditions.

The data, the example models, and all the other information the researchers have about low-head dams, reverse rollers, and risk assessments are being packaged into a single plain-language toolbox intended to be picked up and used by anyone.

“If a stakeholder says, ‘I know of this low-head dam, but I don’t know if it’s dangerous,’ then they can download our toolbox that will walk them through the danger, the data needed, and the modeling efforts.”

Crookston said stakeholders using this toolbox can showcase the data as justification when pursuing grants to improve the safety of the dams.

The national database of low head dams will be hosted by the U.S. Army Corps of Engineers, who already have a database for large dams. The researchers’ efforts have resulted in a low-head dams safety month and increased public awareness like the Association of State Dam Safety Officials’ 2026 campaign. More members of the academic community are also becoming involved, extending the network of experts working on this important issue.

“For me personally,” Crookston said, “it’s really rewarding to work on a safety aspect. It’s nice to be helping with awareness and connecting others to the problem.”

Crookston looks forward to conducting more UAV flights and gathering data on Utah rivers to expand knowledge on the state’s low-head dams and contribute to efforts to prevent further drownings.

More information can be found in the UWRL Annual Report.