FlatironDragados and joint venture partner Aecon finalized a $691 million contract with the U.S. Army Corps of Engineers, Seattle District, to deliver the Howard A. Hanson Dam Additional Water Storage Fish Passage Facility in Ravensdale, Wash.
Employing the Integrated Design and Construction method developed by USACE, this collaborative approach brings together the designer of record and contractors from the early design phase through construction. The model improves coordination, helps mitigate risk and enhances cost and schedule certainty — supporting early alignment among project stakeholders and more informed decision-making throughout the project.
"We are excited to start construction on the Additional Water Storage Project at Howard A. Hanson Dam," USACE Seattle District Commander Col. Kathryn Sanborn said. "Howard A. Hanson Dam serves as our primary line of defense against catastrophic flooding in the Green River Valley, holding a record pool and decreasing peak flood by over 5 feet during the record-breaking flows in December 2025. This project significantly expands our water storage, ensuring a reliable supply for thousands of homes and supporting the future economic growth of the region, while also providing salmon access to nearly half of the Green River habitat above the dam."
"The Howard A. Hanson Dam project is a complex, multi-benefit infrastructure initiative," said Richard Grabinski, FlatironDragados chief operating officer. "In partnership with Aecon, we worked closely with USACE, Tacoma Public Utilities and other stakeholders throughout the collaborative design phase. As we advance to construction, we will continue that approach through the IDaC delivery model that will enable ongoing coordination, proactive risk mitigation and safe, efficient project delivery for the Green River watershed."
Following successful completion of the collaborative design phase, the project now is advancing into construction to deliver enhanced fish passage, ecosystem restoration, water supply reliability and flood risk reduction.
Located about 35 mi. southeast of downtown Seattle, the project will improve passage for juvenile out-migrating salmon in the Green River. The facility will allow salmon to bypass the existing dam, supporting conservation of key species while maintaining flood risk management for the region. The facility will include a fixed multiport collector, steep slope bypass, deceleration tunnel and outfall stilling basin structures. This project enhances environmental resiliency in the Pacific Northwest.
Construction is expected to begin in the second quarter of 2026.
