Rising sea poses more urgent risk to downtown Olympia than previously thought

As sea levels continue to rise, so does the threat of flooding in downtown Olympia. The threat might be more urgent than the city previously believed.

“We’re suggesting a more-heightened sense of urgency in our response,” said Andy Haub, water resources director for the city’s public works department. “The current risk is higher for downtown flooding than previously thought.”

The potential worst-case scenario could leave much of downtown under water, especially areas bordering West Bay and Capitol Lake.

At a study session Tuesday with the Olympia City Council, public works employees outlined the latest projections for downtown’s vulnerability to flooding. No decisions were made.

The annual update included possible steps in developing a more formal sea level response plan.

According to the National Climate Assessment, global sea levels could rise as much as 4 feet by 2100. Other scenarios peg the rise as high as 6.6 feet. The Intergovernmental Panel on Climate Change reports global sea levels have been rising at a rate of 3.2 millimeters per year.

In Olympia, even a 1-foot rise could have devastating consequences, said Eric Christensen, planning and engineering manager for the public works department. To further complicate the problem, downtown Olympia appears to be sinking at a rate of nine-tenths of an inch every decade, he said.

At this time, downtown Olympia is most vulnerable to flooding during high tides such as the one that reached 17.6 feet in December 2012. The city reports the highest recorded tide in Olympia was 18.2 feet Dec. 15, 1977.

If local sea levels rise by 1 foot, downtown Olympia could see major flooding up to 30 times a year. If sea levels rise by 2 feet, flooding could occur more than 150 times a year, he said.

Capitol Lake increases downtown Olympia’s vulnerability to flooding, said Christensen, who noted that the Fifth Avenue Dam is key to controlling floodwaters. Raising the elevation of the adjacent Heritage Park could curb flooding, he said.

Olympia has been discussing the impact of rising sea levels since the early 1990s, and reports have been issued over the years. The topic is addressed specifically in the Comprehensive Plan, which serves as a policy blueprint for the city’s goals.

Haub and Christensen said the city needs to adopt a “first line of defense,” such as requiring elevated floor plans for downtown buildings, modifying storm drains, installing flood barriers or even creating an elevated roadway.

As for next steps, they suggest public outreach as well as working with the city’s Utility Advisory Committee on a program that targets rising sea levels. That includes identifying possible funding sources and financial needs for such a plan.

Rich Hoey, director of public works, said city staff will present a plan of action to the council during a study session in July.

This story was originally published February 10, 2016 at 10:44 AM with the headline "Rising sea poses more urgent risk to downtown Olympia than previously thought."