Advanced American Construction was subcontracted by Skanska USA to perform the marine work for the Puget Sound Energy Floating Surface Collector (FSC) project on Lake Shannon. The 60 foot by 130 foot by 25 foot tall steel structure attracts and safely holds juvenile salmon for transport around the Lower Baker hydroelectric dam. The Net Transition Structure (NTS) funnels the fish to the collector, along with fine-mesh guide nets that extend from shore to shore and from the lake’s surface to its bottom.

Due to the large fluctuation in Lake Shannon’s water depth (up to 68 feet), AAC mobilized in February to construct 6 of the concrete shore anchors while in the dry. Access to these locations was by barge only. Ground conditions required extensive grading work and drilled anchors to tieback the anchors to rock. This work was completed on an accelerated schedule due to a maximum 6 week low water window. Once the water elevation was raised 50 feet, AAC re-mobed to complete the last 4 anchors. Divers were used to connect the chain and Amsteel mooring lines to the shore anchors for pull testing before connection to the structures.
Once Skanska finished fabrication of the FSC and NTS on land, AAC received the structures at the water’s edge to tow to temporary moorage. Once we were allowed to remove the existing collector, AAC towed and connected structures in final location. Pacific Netting Products fabricated the guide net in 7 panels for delivery. Onsite, they sewed the panels together as AAC installed the permanent floats and stored in the water. The 2,300 foot long net was towed out, connected to the NTS opening with divers, then lowered in sections to ensure the net was laying on the lake bottom on the design alignment.

AAC’s dive crew performed over 1,300 hours of dive time to complete this project.