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News / Northwest

Lexington dam project heads into final phase to improve flood protection

By Katie Fairbanks, The Daily News
Published: March 31, 2023, 7:33am

LEXINGTON — A $15 million project is underway to improve flood protection in the growing neighborhood north of Kelso, after more than a decade of planning.

The Lexington Flood Control Zone District hired Nutter Corporation of Vancouver to build up the South Fork McCorkle Creek detention structure at the end of Sparks Drive, according to a district press release. Once complete, the structure will have enough capacity to retain runoff from a 100-year rainfall event.

The neighborhood near the creek has seen some areas of flooding but nothing that did much property damage, which is lucky, said Patrick Harbison, diking engineer.

“Supervisors were smart enough to look ahead,” he said. “They knew as development occurred it would be a problem, so they wanted to get ahead of it.”

The plan

The detention structure normally sits empty of water, but during big storms, the gate is closed so water can back up there rather than overflowing the creek, Harbison said. As the pumps get caught up, the gate is slowly opened, sending water down the creek, he said.

In 2009 engineering firm Gibbs and Olson completed a study for the district identifying the best way to maintain the level of flood protection inside the levy with additional development coming in, Harbison said.

The study looked at three options: adding pumps to the McCorkle Creek pump station, constructing a tunnel to Dorthy Lake and increasing the dam height, Harbison said. The third option was recommended as the most economic and efficient engineering-wise, he said.

It took 10 years to get a permit from the U.S. Army Corps of Engineers, which was not an unreasonable length of time, Harbison said. Area legislators helped push the federal agency to issue permits, he said.

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The district split the project into three construction phases because of funding concerns, Harbison said.

The first phase, completed in 2020, was to preload the area on the north side of the creek that didn’t previously have a dam.

In October, crews began the second phase of building the basic structure of the new section to the same height as the existing dam. Construction is expected to wrap up in mid- to late-May, Harbison said.

The third phase will include raising the entire structure by 13 feet and replacing spillway and outfall piping. Harbison said the district hopes that construction will begin late this year or early next year.

“They were looking ahead when they designed it but the need is here,” he said. “The last big parcels are being constructed on and all that water heading toward pump station, so the need for it is here. That’s why we’re pushing so hard to get it done in the next year.”

To help fund the project, in 2018 the diking district received a $4.7 million Public Works Trust Fund loan with a low-interest rate that it will pay back over 20 years. Increasing construction costs mean the district is using more of its own money on the project, but assessments will stay steady, Harbison said.

The district is looking for funding options to complete the $15 million project, potentially through a state loan or grant, he said.

“The district does understand it is a big impact on lives, the traffic that’s going through,” Harbison said. “We appreciate peoples’ patience and hope to finish as soon as possible.”

How to learn more

Residents can reach Harbison with any questions at 360-577-3030 ext. 6536 or harbisonp@cowlitzwa.gov.

The Lexington Flood Control Zone District board meets the first Monday of each month at the Public Works Administration Building, 1600 S. 13th Ave., Kelso.