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Multnomah County’s downtown Portland bridges need extensive maintenance and seismic upgrades to remain operational over the next 20 years, but they won’t come cheap, according to county engineers.

A recently released draft of the updated Multnomah County Willamette River Bridges Capital Improvement Plan recommends 53 projects totaling $1.3 billion. The plan looks at the current conditions and maintenance needs of the county’s six crossings over the Willamette River between 2015 and 2034 and the bridges’ risks of sustaining damage in an impending high-magnitude earthquake near the Oregon coastline.

Plan recommendations include seismically retrofitting the historic Broadway, Burnside, Hawthorne and Morrison bridges. All four bridges are in danger of failing in a high-magnitude earthquake, county engineer Brian Vincent said on Thursday in a briefing to the Multnomah County Board of Commissioners about the plan.

鈥淚t’s not unreasonable to assume this could happen,鈥� he told county commissioners. 鈥淚t’s time to do something now. They are vulnerable. I think we understand that. There is something to do about that. Unfortunately, it’s phenomenally expensive.鈥�

The draft capital improvement plan is available on the county website and officials are seeking additional public comments through an online survey before finalizing the document in June. It will then be integrated into the county’s transportation improvement plan.

In recent years, county officials have focused on replacing two of the neediest bridges. The Sauvie Island Bridge was rebuilt in 2008 and the new Sellwood Bridge is scheduled to open in January 2016. The updated capital improvement plan centers on the county’s four other bridges 鈥� the Broadway, Burnside, Morrison and Hawthorne 鈥� and includes seismic evaluations of them. All four are listed on the National Register of Historic Places. The Hawthorne and Broadway bridges are more than 100 years old.

鈥淢ost importantly, this is a road map over the next 20 years, what to do with these aging structures to keep them in service,鈥� Vincent said.

A top priority in the plan will be spending $547 million to either seismically retrofit or replace the Burnside Bridge so it can withstand a high-magnitude earthquake. The crossing takes precedence in the plan because it has been designated as a regional lifeline over the Willamette River that should remain intact after an earthquake, Vincent said. The plan calls for less robust seismic upgrades to the Broadway, Morrison and Hawthorne bridges.

Recommended funding for bridge projects over the next 20 years would be split between $650 million for seismic resiliency work and $650 million for preservation and maintenance efforts.

The $547 million price tag for work on the Burnside Bridge is the highest in the plan followed by an anticipated $236 million to repair the Morrison Bridge, $212 million for the Broadway Bridge and $195 million for the Hawthorne Bridge. The newer Sauvie and Sellwood bridges would require less maintenance and upkeep over the next 20 years, and are anticipated to total $3.9 million and $1.5 million, respectively. The plan also calls for spending $70 million in projects on multiple county bridges.

David Evans and Associates Inc. Vice President Mike Baker, who contributed to the plan, told county commissioners developing the document involved a comprehensive assessment of the condition of each crossing and gathering input from various stakeholders. Needed projects were then identified and prioritized based on factors that included the cost, available funding, urgency, and benefits of the improvements.

Projects outlined in the plan favor preserving the county’s aging bridges instead of replacing them, Baker said.

鈥淲e were aware of the iconic, historic nature of the bridges,鈥� he said. 鈥淟et’s make good use of what we have before we replace.鈥�

Top priority projects in the plan include completing a feasibility study this year for work on the Burnside Bridge, a rehabilitation effort in 2016 and a seismic upgrade in 2017. County officials plan to paint the Broadway Bridge in 2015 and replace the rall wheels in 2016. A paint and structural rehabilitation of the Morrison Bridge is planned for 2017.

The estimated $1.3 billion cost of preserving and retrofitting the county’s bridges may be daunting, but the plan calls for breaking it down into manageable chunks, said Ian Cannon, county bridge engineering services manager.

鈥淭hat’s a lot of money over the next 20 years,鈥� he told commissioners. 鈥淭he good news is it’s smaller at the front end so it’s more approachable. That’s really key 鈥� starting now to make sure we have success later in the program.鈥�

The need for the county to invest in its bridges is evident in how often the structures are used, Cannon said. The four downtown Portland bridges combined experience 200,000 daily crossings, he said.

County Commissioner Judy Shiprack said hearing that fact helped her justify the high cost of maintaining the bridges.

鈥淭his is not a political discussion. This is an engineering discussion,鈥� she said. 鈥淭hat number is phenomenally expensive, but again we’re dealing with something that’s phenomenally used.鈥�

The plan outlines the urgency for seismic upgrades to the bridges, Commissioner Jules Bailey said.

鈥淚 think it’s clear that we have to act,鈥� he said. 鈥淵ou’ve shown us that we can’t wait.鈥�