Bonneville Fishway Repaired Debris Tore Gratings Loose; Search On For Trapped Fish

The Army Corps of Engineers had repaired damage to a fish passageway at Bonneville Dam and planned to reopen it by this morning, a corps biologist said Monday.

“We noted in July that there were diffusion gratings, which are on the floor of the facility, that had been displaced due to debris,” said Gary Johnson, fish biologist for the corps in Portland.

Debris carried by spring runoff had torn away the gratings, which cover an auxiliary water system that feeds the fishway.

“The gratings are for adding water to the fishway. They keep fish from going into that part of the system.”

Divers since have replaced 20 gratings - about one-fourth of the gratings in the fishway on the north side of the second powerhouse.

Corps officials tried to track fish that might have found their way into the water conduit below the sluiceway. Biologists at one point estimated that as many as 1,000 fish might have been trapped beneath the dam.

But the large numbers of fish didn’t materialize, Johnson said. No radio-tagged fish have been detected.

“In one part of the system, we’ve seen a couple of sturgeon and steelhead. One came out during the special operation,” he said.

“As far as the number of fish, there’s no way of knowing whether there are fish in there,” he said.

Hydroacoustic testing will continue to determine, by sound, if any fish are trapped in the conduit, Johnson said.

At the same time, the corps must “take whatever steps we can to get the fishway into operation for the steelhead run that’s getting under way right now and the fall chinook run that will be there shortly.”

The fish ladder will resume operation for now without auxiliary water being pumped through the grating, he said.

The swift flow of extra water in the fish ladders is meant to attract salmon and steelhead, which instinctively fight the flow to swim upstream to their spawning beds.

However, even without the extra water, Johnson said, biologists tagging fish at the dam have found a sufficient number drawn to the ladder.

The National Marine Fisheries Service and the University of Idaho are tagging fish that will be released five miles downstream from the dam. The fish then will be tracked all the way to their headwaters.

News that the fishway had been damaged initially had caused fears that the second powerhouse would have to be shut down to repair the fishway during peak summer electricity usage.

The No. 2 powerhouse at Bonneville, 36 miles east of Portland, produces 600 megawatts of electricity, enough to serve the city of Portland.