Bonneville project to reduce nitrogen levels
by Jeremy Vesbach

The Portland construction company Advanced American Diving is currently at work on a $4 million project at the Bonneville Dam that the U.S. Army Corps of Engineers hopes will make the river downstream more hospitable to fish and other aquatic life.

The construction company is placing a new type of flow deflector in six of the dam's 18 spillways. Flow deflectors, located at the base of a spillway, prevent water from plunging deep into the river where it can cause high levels of nitrogen to become trapped in the water. High nitrogen levels can cause a variety of problems for aquatic species, including a condition in migrating salmon and steelhead similar to the bends in humans. Federal and state water quality standards set dissolved gas super-saturation limits at 110 percent.

If testing finds the six new flow deflectors to be effective in reducing total dissolved gas levels, the Corps may replace flow deflectors in the remaining 12 spillways.

The original flow deflectors were installed at 14 feet above sea level, at a time when it was assumed water would only be spilled over the top of the dam and bypass the electricity-generating turbines when water levels were so high it had to be spilled.

To improve the survival rate of migrating salmon and steelhead, the Corps began spilling water over the dam even at times when high water levels did not demand it. The new flow deflectors will be set seven feet lower than the existing flow deflectors. The new deflectors also have a slightly different shape intended to reduce dissolved gas levels even further.

The project is scheduled for completion by March 10. Advanced American Diving was not able to start the project until later than originally planned due to later-than-normal spills conducted after the summer's energy crunch.

Despite the late start and tightened security measures, Darren Funk, Advanced American Diving project engineer, said the project is on schedule.