Guidelines developed for hydraulic design of safer canoe chutes

CHAMPAIGN, Ill. — With the advent of warmer weather, many outdoor enthusiasts are taking to the water in canoes and kayaks. Some boaters, blocked in their travels by one of the myriad dams that dot the nation’s waterways, may attempt to navigate the spillway – a dangerous practice that could result in death by drowning in the strong undertow that forms at the base of a dam. Scientists at the University of Illinois have a safer alternative: properly designed passageways called canoe chutes.

"For well over a century, low-head dams have been constructed for such purposes as flood control, crop irrigation and to provide power for mills and factories," said Marcelo Garcia, a UI professor of civil and environmental engineering. "With the recent rise in recreational use of our rivers and streams, these structures must now be modified to accommodate safe passage for boaters."

By using a combination of computational fluid dynamics and laboratory experiments, Garcia and his colleagues – graduate students Marjorie Caisley and Fabian Bombardelli – are creating safe and efficient designs for retrofitting dams with canoe chutes.

Erected in an existing spillway, the basic design of a canoe chute consists of a series of steps or rapids connected by larger pools of slow-moving water. Each pool must be long enough to allow the water to slow sufficiently so that a boater can recover from the previous drop and prepare for the next. The pools also must be deep enough for a kayaker to roll over without the risk of head injury.

"The most important design consideration for building a canoe chute is safety," Garcia said. "The passageway is not intended to be an artificial whitewater course, so one of the biggest challenges is making it safe for boaters over a wide range of seasonal flow rates." To create better guidelines for the construction of canoe chutes, Garcia’s team subjected a basic chute design to intensive testing with a powerful three-dimensional numerical model called Flow-3D, developed by Flow Science Inc. Using the model, the researchers could simulate turbulent flows and study the formation of dangerous eddies and undertows in their steps and pools.

"This numerical procedure allowed us to save a lot of time, effort and money over building numerous physical models by trial and error," Garcia said. "By analyzing different flow conditions and geometrical aspects of the canoe-chute design, we could obtain an optimal structure."

The researchers then built a physical model of the optimized design, and compared its performance with their numerical predictions. The physical model verified the numerical model and validated the empirical method for predicting hydraulic behavior in canoe chutes.

"Properly designed canoe chutes can not only increase the safe, recreational use of rivers and streams," Garcia said, "they also can serve as fish ladders, facilitating the migration of fish."

The Illinois Department of Natural Resources, Office of Water Resources, funded Garcia’s work.