Portland’s Willamette River Crossing to Ensure Resilient Water Supply

By TBM Staff September 10, 2019

Portland’s water mains that cross the Willamette River are more than 50 years old and will probably not survive a major earthquake. The Willamette River Crossing Project, which will build an earthquake-resilient water main deep under the Willamette River, is part of the City of Portland Water Bureau’s commitment to preparedness. This new water pipe will help ensure that we can deliver safe and abundant water to the west side, even after an earthquake.

The greatest seismic hazard to existing river crossings is a Cascadia Subduction Zone (CSZ) earthquake. It’s been 317 years since the last CSZ earthquake, and there is a 30–35 percent chance its fault will rupture in the next 50 years.

In May 2019, the design/build team of James W. Fowler Co. and Stantec Consulting was given notice to proceed on this challenging project. Currently in the design phase, there will be a geotechnical probe performed this fall to provide information about the soil conditions under the river and help the team determine the best path for the pipeline.

The team was selected because of its innovative proposal to combine two modern construction methods—horizontal directional drilling and microtunneling—to bury pipe deep in bedrock, where it will be more protected from earthquake risks and have less impact on businesses, the public, and the environment.

The river crossing is anticipated to have a length up to 4,500’ and a depth of about 80 ft below the bottom of the river. The length and width of available staging for pipe laydown, assembly, and pullback is constrained by limitations on available city street right of way.

Besides the river crossing, the project includes variable lengths of open cut construction to connect into existing pipelines that are referred to as the west side and east side headers. Pipeline appurtenances, including isolation valves, will be required at the connection on both sides of the river.