A $5.9 million city of Kent project to improve the Upper Mill Creek Dam will help reduce flooding and restore salmon populations.
The City Council unanimously approved a low bid on Aug. 7 by Aberdeen-based Quigg Bros. Inc., to raise the height of the dam by about 5 feet along the east side of 104th Avenue Southeast near Southeast 267th Avenue, according to city documents. Crews will add a reinforced concrete wall to the top of the dam to increase flood storage by about 50 percent and install a fish ladder.
“It’s one of a multitude of projects to help solve the flooding downstream in Mill Creek which floods 76th Avenue and Woodford Avenue,” said City Public Works Director Tim LaPorte to the council. “We will be raising the dam, installing a fish ladder and doing a lot of concrete work.”
Other projects by the city include dredging Mill Creek in 2020 to reduce flooding in the Kent Valley – an estimated $10 million project.
Crews will begin work on the dam with utility relocation this year, but most of the construction will be done next summer.
“As the dam is an active stormwater flood control facility, there is a narrow seasonal construction window that we have available to perform the work,” said City Engineer Steve Lincoln, who is overseeing the project, in an email. “Therefore, we expect construction to take up to two years, with completion in 2020. However, the dam will be functional at current capacity during the wet season.”
Kent received six bids for the project, with the highest coming in at $7.8 million. City officials estimated the cost at $5.3 million.
“The engineering estimate didn’t account for inflation,” LaPorte said.
The city will pay for the project from its drainage fund. Residential rates are $12.51 per month for the storm drainage fee. Commercial businesses and multi-family complexes pay a fee based on impervious surfaces.
Crews built the dam in 1974. The dam was upgraded to its current structure in 1989, Lincoln said. The improvements will increase flood storage to about 150 acre feet or 49 million gallons.
“The dam provides flood risk reduction in the area spanning from Earthworks Park to Central Avenue and from Titus Street to James Street,” Lincoln said. “This area includes the Kent Senior Activity Center, Mill Creek Middle School and a number of homes and businesses along Mill Creek.”
Fish passage is included in the project to comply with environmental permitting requirements from the state Department of Fisheries, the U.S. Army Corps of Engineers and from consultation with the Muckleshoot Indian Tribe, Lincoln said. The original dam and flow diversion structure does not have a formal fish ladder facility.
“The new fish ladder included with this project will increase opportunities for fish habitat and passage to other reaches of Upper Mill Creek,” Lincoln said.
When the work is done in a couple of years, residents should see a difference.
“We are really looking forward to completing this project,” Lincoln said. “It will reduce flooding along Mill Creek in concert with the Mill Creek Reestablishment Project (dredging, diversion of the creek) that is currently in design. The dam improvements will also aid in the ongoing regional efforts of restoring Puget Sound’s salmon populations.”