TribTown: Columbia’s drainage can
handle heavy rains
Experts have confidence in system’s overflow capacity
By ANNA JOHNS
Issue date: Tue, Jan 31, 2006
The Tribune
While some homeowners in Portland are wary as they watch the water rise in
nearby creeks and rivers, managers of the Columbia River flood plain aren’t sweating
this winter’s wet weather.
The Multnomah County Drainage District manages all the water that flows through
13,000 acres of flood plain, from the Sandy River to the Rivergate Industrial District
at the Port of Portland. It also maintains 37 miles of levees that keep the Columbia at
bay.
“Basically the drainage district is nothing but a big bathtub,” Deputy Director Dave
Hendricks said.
The Columbia flood plain lies on bowl-shaped land, similar to the landscape of the
city of New Orleans, which flooded when its levees failed following Hurricane
Katrina last September.
While the layout of the land is similar, the levees are very different. Columbia River
levees are of “earthen design,” or sand, which soaks up water and allows some of it to
pass into the flood plain. In New Orleans, the levees were a combination of earthen
design and flood wall. They were built only 1 foot higher than flood level, a
difference called freeboard.
“If we have a 500-year event, we still have 11 feet of freeboard,” Hendricks said.
Still, the drainage district is considering making the levees higher and wider in the
future to provide even more strength to the structures and prevent erosion of the sand.
In 2003, the district completed an $8.5 million bond project to update its pump
stations.
Eleven pump stations now run on computer programs that measure water levels in
the Columbia Slough and drainage ditches. The programs detect when water levels
rise and pump accordingly. During flooding, the pumps can move 1 million gallons of
water per minute.
“Right now we’re pumping 200,000 gallons (per minute),” Hendricks said. “We’re
not even close to maximum.”
While the drainage district has spent millions of dollars to update and streamline its
operations, it’s currently in a holding pattern on one major project that will save
money on operating costs and improve the environment. The district plans to lower
the banks of 22 miles of ditches that carry storm water to the pump stations. This will
widen the ditches, creating more water storage capacity and a wetlands habitat.
“We store the water rather than having to pump it out real quick, which saves
money on electricity and maintenance costs,” Hendricks said.
The district started construction on the ditches five years ago but hit a roadblock
with the city of Portland’s environmental zone rules. Officials have been working to
reword the environmental zone rules to allow for the project, but the city’s Bureau of
Planning said a change in code is still one or two years away.