The latest work to improve fish passage under state roadways in Skagit County is set to begin Monday in the Concrete area.
The state Department of Transportation this summer will replace two, 2-foot diameter culverts under Highway 20 — one on Lorenzan Creek in Concrete and the other on Fish Creek in Grassmere.
Transportation spokesperson R.B. McKeon said the cost of the projects is a combined $3.6 million.
On Monday, crews will begin work on the undersized culvert on Lorenzan Creek near Dalles Road.
The work will affect traffic and require a closure of the Cascade Trail between North Superior Avenue and E Avenue, according to a news release.
Highway 20 through that area will be rerouted onto the Cascade Trail as single-lane, alternating traffic 24/7 during construction. Cascade Trail pedestrians and bicyclists can take a 0.7-mile detour using Concrete’s Main Street.
The 2-foot diameter culvert will be replaced with a three-sided, bottomless structure 16 feet wide by 48 feet long. According to Transportation’s Fish Passage Inventory map, that will open about a mile of stream habitat for fish.
After the Lorenzan Creek project is completed, the undersized culvert at Fish Creek near the Grassmere Fire Station on Highway 20 will be replaced. Transportation officials plan to start that work in September and to build a temporary bypass road adjacent to the highway.
The Fish Creek culvert will be replaced with a box structure 19 feet wide and 44 feet long. According to the map, that will add access to 1.5 miles of fish habitat.
McKeon said Lorenzan and Fish creeks, both part of the Skagit River watershed, are used by various kinds of salmon and steelhead. Bull trout have also been documented in Fish Creek.
Project Engineer Melissa Ambler said the culverts currently beneath the highway don’t support the depth or velocity of water needed to allow fish to swim through. A formula was used to determine the size of the box culvert to put in.
“There is a lot of science behind it, and we feel this width is what is going to encourage the fish to come back through,” Ambler said.
The culvert replacement projects are the latest meant to correct barriers to fish passage under roadways throughout the state. A 2013 U.S. District Court decision made such projects mandatory.
In Skagit County, the first project aimed at compliance with the ruling was done in July 2015 where Lake Creek flows beneath Highway 9. The second was in September 2017 where Fisher Creek flows beneath Interstate 5.
Additional projects took place on Gribble Creek under Highway 9 in July 2018 and on Carpenter Creek under a private road in September 2019, the latter with support from a state grant program meant to help property owners comply with fish passage requirements.
Fish passage improvements were in progress prior to the court ruling, but have since garnered more attention and funding.
McKeon said in an email in June that the state has allocated about $1 billion for these kinds of projects to be completed between 2019 and 2023.
Additional local fish passage projects are being planned for areas of Highway 9, Highway 20, Highway 534 east of Conway and Highway 538 (East College Way).