City to Dredge Lower Cedar River this Summer

Thanks to a grant form the King County Flood Control District, the city of Renton is planning to do some dredging on the lower Cedar River this summer that officials say is not only overdue but should reduce the risk of seasonal flooding.

The plan is to remove 120,000 cubic yards of gravel that has accumulated on the river bed since the last time the river was dredged in 1998. The dredging will occur on a 1.25-mile stretch of the lower Cedar from Lake Washington to the Williams Avenue Bridge.

“Rivers move gravel, it’s a natural process,” Renton Surface Water Utilities Manager Ron Straka said recently.

According to Straka, following extensive flooding of the river in 1990, an environmental review by the Army Corps of Engineers showed that dredging the river, along with constructing levees and flood walls, was the best solution to the flooding issues.

In the Cedar, which is a man-made channel built in the early part of the 20th century, the grade of the final stretch is relatively flat and the river regularly deposits debris from the upper reaches in that stretch as the water slows down before entering the lake.

Straka said the plan is to work from the airport side of the river, its east bank, so as to keep the parks and trails on the west side open, though some temporary closures may be necessary through the course of the project.

“Our goal is to keep the trail open if possible,” he said.

Straka said along with the dredging, mitigation plans also include bank stabilization work and new habitat plantings along the banks.

The work will be done with a trapazoidal dredge with an average depth of 4 feet. There will be a gradual slope from the North Boeing Bridge to Logan Avenue, with a steeper transition from Logan to Williams Avenue.

Straka said the city was currently advertising for bids on the project, which is expected to cost between $7.8 million and $8.6 million. Work is expected to begin mid-May, but the in-water work can only legally take place between June 15 and Aug. 31, so the dredging is completed before the salmon begin this fall’s spawning run.

The project will be funded by a grant form the King County Flood Control District.

Source: Renton Reporter.com