Water Bureau to build new pipe deep below Willamette, current pipes could fail in quake

PORTLAND, Ore. — The Portland Water Bureau says a Cascadia Subduction Zone earthquake could ruin or damage the pipes that bring water from the east side to customers and businesses on the west side. Their solution? Dig deeper.

The problem, according to Tim Collins, a geotechnical engineer with the bureau, is liquefaction. The pipes sit in the very soft soil around the Willamette River. It’s the same soil much of inner-Portland is built on. In a large earthquake, that soil can liquefy, causing major damage, and water pipes to break.

“It's likely they will have some damage, some impact to capacity, some of them will be completely broken,” said Collins.

There are currently six pipes delivering water to the west side. Some go underneath the river and some are on the Ross Island Bridge. According to the city documents, their greatest concern is the three central city crossings which have a 48 percent chance of failing simultaneously during a Cascadia quake.

Collins has been working on what’s known as the Willamette River Crossing Project. To fix the liquefaction problem, the bureau is digging a water line deeper underneath the river to avoid the soft soils.

“We're going into the solid bedrock, then up on the other side, avoiding these really loose-filled soils sitting on either side of the Willamette,” said Collins.

The pipe will be about 4,500 feet long, and sit 80 feet below the river bottom.

The bureau is expected to pay a contractor $73.5 million. City Council will vote on approval of the contract Wednesday. Collins says the entire project will cost closer to $90 million. The bureau will not need to ask for more money to complete the project.

Construction is expected to begin in about 12 to 18 months. Contractors will use what’s called Horizontal Directional Drilling, or HDD. No work will be done in the river.

The new pipe would become the backbone of Portland’s water system, and provide a reliable source of water to the west side in an earthquake. There are about 32,000 customers on the west side, three hospitals, one-third of employment, and billions of dollars in economic activity.

“I went to New Orleans. I know what it's like for a city to not have water for months. That is not a good place, and we don't want to be like that here. So, we need this,” said Collins.

Dan Douthit, a spokesperson for the Bureau of Emergency Management, says anything the city can do to prepare is a good thing. He says they look to other cities for inspiration, like Alaska.

Two weeks ago, Alaska dealt with a 7.0 magnitude quake that caused severe damage. Alaska is also home to the largest earthquake in U.S. history.

“They've been able to rebuild and get everything up and running so quickly because their infrastructure is in a better spot than ours, and their building codes are stronger,” said Douthit.

He says it takes years for a city like Portland to improve its infrastructure, and this is one step of many the city needs to take.