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Hells Canyon Dam on the Snake River in Idaho (Photo Courtesy of the U.S. Bureau of Land Management).

Hells Canyon Dam on the Snake River in Idaho (Photo Courtesy of the U.S. Bureau of Land Management).

IIHR Associate Research Engineer Marcela Politano and her team are conducting a number of research projects that contributes to systems that help fish pass safely through these dams. Politano’s research team is working on a number of research projects related to total dissolved gas and hydropower. Hydroelectric power does not produce greenhouse gas emissions; the electricity is generally available as needed; and the reservoirs can be used for numerous purposes, including recreation.

But hydroelectric power can have negative impacts as well. One of these environmental concerns is total dissolved gas (TDG), or the amount of gas present in water. Elevated TDG can occur immediately downstream of the dam—known as the tailrace—and farther downriver. Elevated TDG harms many aquatic species, including salmon. Fish exposed to water with elevated TDG can develop gas bubble disease.

Politano’s research focuses on numerical modeling of TDG. Water flowing over a dam can become supersaturated with gas as the water plunges to extreme depths below the dam. “The severity of the effect depends on the level of TDG and exposure time,” she explains.

Politano developed the first two-phase numerical model to represent the complex physics of a dam’s tailrace. Her model can also evaluate technologies designed to
reduce TDG and protect fish. For instance, spillway flow deflectors designed at IIHR redirect spill water to form a surface jet that prevents bubbles deep in the tailrace.
The numerical model allows testing of these technologies before construction begins.


Last modified on September 26th, 2012
Posted on March 15th, 2012