Chelan County PUD - Rock Island Adult Fishway Extension

Dive barge in front of powerhouse at Rock Island Dam
Dive barge in front of powerhouse

Rock Island Dam is located on the Columbia River, approximately 15 miles south of Wenatchee, WA. The development of a crack in a spillway of Wanapum Dam, downstream of Rock Island Dam necessitated a 25 foot drawdown of the tailrace. This created a significant obstacle for the fish migrating upstream; they would not have access to the original fish ladder. With the arrival of the migrating salmon just a few months away, this project took on a critical path very quickly.

Chelan County PUD, owners of Rock Island Dam, contracted Knight Construction from Spokane to install the emergency fish ladder extensions in three areas, two on the west bank and one on the east. Knight, who handled the fabrication and topside support, turned to Global Diving & Salvage, Inc. to provide the diving support for the project. With the compressed schedule required to complete the project, Global and Knight worked closely on scheduling the arrival of the fabricated items and their installation.

The extensions, similar to the structural components of the original fish ladder structure, consisted of steel boxes and flumes used to create pools and steps. These new boxes and flumes were mounted to the face of the dam and in the case of the east side, were suspended from a pipe that spanned two pier noses. The project involved a wide array of construction techniques, including; core drilling, setting of epoxy and mechanical anchors to secure the boxes and frame work in place, wall sawing to remove sections of the dam to allow access at the lower water levels. The steel sections were bolted and in some cases welded in place.

By all accounts the project has been a great success. According to the Wenatchee World, over 20,000 of the expected record 235,000 Chinook salmon migration have already traveled upstream past Rock Island Dam.