News Release
| Release Number: | 97-085 |
| Dated: | 8/6/1997 |
| Contact: | Heidi Y. Helwig, 503-808-4510 |
Portland, Ore. -- Today, the U.S. Army Corps of Engineers will brief the region's Technical Management Team for fish on the Corps' decision to begin operating Bonneville Dam's second powerhouse fish ladder and auxiliary water system by the end of this week. This decision, made in cooperation with regional fisheries and resource agencies, came after extensive hydroacoustics sampling indicated there are fewer fish in the auxiliary water supply (AWS) than estimated earlier.
"This data tells us there are very few adult salmon in the AWS," said fishery biologist Gary Johnson. "Based on the numbers and size of fish we detected, and the difficulties of successfully dewatering the AWS and salvaging fish in the current high water temperatures, we opted to move forward for the sake of the upcoming fish passage season. Our immediate goal is to get the entire north shore fishway into full operation as quickly as possible." The fish ladders will operate until fall when fish counts decline enough to allow safe dewatering of the system.
"We're sad if we lose any fish, but at the same time, it's essential that we are ready for the steelhead and Chinook fall runs underway now and that will peak in early September," Johnson said. "When it's safe to dewater, we'll go into the dam's AWS, clean out all the debris and remove any fish." The project's dredging operations in the dam's forebay area also will begin at this time.
In addition to the difficulty of dewatering the system now, there would not be enough time to clean out the AWS and rewater it before the fall fish runs reach Bonneville, Johnson said. "We're confident the north shore fishway, with one fish attraction turbine working, will allow the system to operate successfully and allow continued fish passage until fall," he said.
Operation of Bonneville Dam's second powerhouse main units will be a topic of discussion with the regional team this afternoon.
Since the debris problem has not been eliminated, divers inspected the diffuser gratings this morning and removed some gratings in an area of the AWS inaccessible to fish. Removal of these gratings should alleviate any pressure buildup from additional debris to avoid dislodging any more grates. A monitoring plan is being developed and will be implemented to ensure the gratings remain attached.
Because of the ongoing work in the area, the Cascades Island fish area will be closed to the public through Monday and will reopen on Tuesday, Aug. 12.
Earlier Monday, the Corps curtailed its special operation of creating "upstream" flows to attract fish out of the AWS. The flows were created between Thursday, July 31 and Monday, Aug. 4, and produced one steelhead.
High flows and large amounts of debris brought down in the Columbia River this summer caused gratings on the floor of Bonneville Dam's second powerhouse fish ladder to dislodge. This provided an opportunity for fish to enter the AWS, which does not allow fish passage over the dam. Adult fish continue to pass the dam through other ladders on the project.
When divers surveyed the fish collection channel beginning on July 21, they discovered 25 grates had been pushed out of place due to excess pressure caused by debris buildup.