Imagine being a leaf floating gently along the surface of a river. Suddenly, the current swiftly carries you overtop a towering waterfall. You plunge downward smashing deep into the pool below where the muffled roar envelops you in a foaming bath of tiny bubbles.
Those bubbles, made up of oxygen, nitrogen and other gasses found in the air we breathe, can and often are absorbed into the water. That’s not a problem—unless too high a saturation level occurs. If so, these high levels of dissolved gases can be potentially harmful to fish living downstream.
It’s why last April through December 2016, we completed an $11 million construction project at Long Lake Dam under its Spokane River Project License. Water testing below the dam showed elevated levels of air dissolved in the river during times the dam spills a lot of water. Avista, working with the Department of Ecology, Spokane Tribe, and many other stakeholders, decided to improve those river conditions.
We installed deflectors on the lower face of the dam to make the water skim instead of plunge at the dam’s base. They also reduced the depth of the dam’s plunge pool and removed rock at a nearby outcropping so it would not obstruct the flow of the river. Together, these changes should lower dissolved gas levels in the water and keep the fish healthy and happy.
This past March through June, we began monitoring dissolved gas levels in the water to test how well the deflectors work. Initial results indicate the modifications have helped to reduce dissolved gas levels downstream of the dam, often below the incoming levels. We will continue to monitor dissolved gas levels through next year to further document how well the modifications are working.