A drop in temperature didn’t stop work this week from occurring on the $343 million Twin Ports Interchange reconstruction project.
Instead, the rat-a-tatting hammer of steel sheet pile being driven into the earth filled the air in Lincoln Park.
A hard-hatted Pete Marthaler stood along the bank facing the St. Louis River, pointing out the subjects of the day.
“This is Coffee Creek; that's Miller Creek,” the major projects construction manager for the Minnesota Department of Transportation in Duluth said, pointing to outlets of water not far from each other. “So what we’re doing now is enclosing the outlet end of the new combined outlet.”
The rerouting and merging of the creeks is among the most complex and challenging aspects of what will be four years of reconstruction.
The News Tribune spoke with engineers to better understand the project — learning about the history of underground creeks in Duluth, the fish involved, and how the new work is an improvement for the way it will introduce an open channel of Coffee Creek through the lower part of the neighborhood for the first time since 1891. Miller Creek is open near the Duluth Transit Authority bus garage.
"We're creating an open channel area of Coffee Creek, before it gets to Miller Creek, which will be beneficial to the native fish," Marthaler said.
It’s necessary to divert Coffee Creek, because its current configuration bends through a field of Interstate 35 bridge piers where hundreds of ground improvement columns will be installed as crews demolish the "flyover bridges" of I-35 and rebuild it at ground level.
The rerouting of the creeks will be some of the first work visible to travelers next spring and summer. It will cause I-35 to be brought to single-lane traffic in each direction throughout the summer to accommodate the work in the neighborhood between 21st and 27th avenues west.
"Starting in April, we’ll be working on both the outlet end and switch traffic so we can work on the inland end, too," Marthaler said. "We just don’t have enough real estate to put four lanes of traffic out there, so we have to have one lane each way."
Next fall, I-35 will reopen to four-lane traffic, after lower Michigan Street is prepped over the summer to become the southbound bypass.
The new combined outlet for Coffee and Miller creeks into the St. Louis Bay will require a subtle shift of Miller Creek. Meanwhile, a new Coffee Creek path through Lincoln Park will be heavily excavated for hundreds of feet to merge into a new four-channel box culvert that will run under Interstate 35.
“It’s an element that we as a project team had to put our arms around and mentally wrangle with it — how we’re going to do this in the most efficient and economical way that’s sensitive to the environment,” Marthaler said.
The new open channel portion of Coffee Creek was a requirement with the Minnesota Department of Natural Resources telling MnDOT that if it was going to have to reroute the creeks, they’d need to be improved.
“One of goals for the DNR throughout the whole project was for Miller Creek to have fish-passable culverts,” Matt Meyer, MnDOT environmental coordinator, said. “We had an opportunity to do something positive here.”
Miller and Coffee creeks originate near the airport and old Shopko, respectively, snaking their way down through Lincoln Park before outlets into the river just north of the Western Lake Superior Sanitary District campus.
Storm water mixes with creek flow on the way down. Food washes down the creeks, too, bringing steelhead trout and other fish into the culverts as far up as the Miller Creek waterfalls in the neighborhood park.
“It’s not what we think of as picturesque,” Tom Johnson, senior engineer with the city of Duluth, said. “But it’s shaded, so it’s cool and it’s got food that washes down.”
The new four-barrel culvert offers three times the current capacity and will replace culverts currently filled with water as the Lake Superior water level remains historically high. When lake levels drop, the new culverts are designed to keep a recess of water for fish to travel.
Johnson is a veteran of Duluth’s underground creek and storm water tunnel network. He called Duluth "blessed" to have 16 trout streams which Johnson said never managed to converge because Duluth is so steep.
The creeks most central in the city, such as Miller, Coffee, Brewer, Clarkhouse and Chester creeks, have portions buried in the name of development in the late 19th century, starting in 1891, in ways that couldn’t be done today.
“These streams were close to downtown and they were ravines, so they would build these stone brick tunnels and fill over top," Johnson said. "They wouldn’t have to build a bridge over a stream that way.”
Only as one moves farther east and west do creeks in Duluth remain completely open to the world, Johnson said.
Johnson described the network of tunnels throughout Duluth as being made with rows of brick arches and polished stone walls. As residents began to populate up the hillside, they continued to bury the creeks themselves in corrugated steel, cast iron or concrete pipes. Some city residents can hear the creeks flow beneath their homes during a heavy rain.
The tunnels run thousands of feet each, with lengths that can be walked by a person. Marthaler showed the News Tribune different points near Piedmont Avenue and West Third Street where running water disappeared into yawning tunnel openings leading underground from the rocky creek beds.
“The craftsmanship of the storm tunnels — they’re in perfect shape,” Johnson said. “To build something like that today, we don’t have stonemasons of that era.”
Sadly, the old brick and stone portions of Coffee Creek being abandoned will be destroyed and filled in as part of the project.
“They don’t want voids underneath the new I-35 roadway,” Johnson said.
New culverts for Coffee Creek will be installed underneath and along 22nd Avenue West for two blocks between West First Street and Michigan Street across two construction seasons beginning next year.
This won’t be the first time Coffee Creek has been diverted. It was rerouted to avoid bridge piers when the interchange was built in 1967.
Work to construct the massive sections of four-barrel culvert by the river will start on both sides of the freeway beginning next spring until October 2021. The middle section of four-channel culvert will be installed between October 2021 and October 2022.
Currently workers are focused on the new outlet of the creek, adjacent to Miller Creek’s current outlet into St. Louis Bay. The current Coffee Creek outlet is about 30 yards away.
“They’re building a cofferdam, so once they get all the sheet piling in it will hold back water,” Marthaler said. “They can pump out the water in the middle, so they can build all the way inside and it’s dry.”
Work on the Twin Port Interchange reconstruction project is expected to last until 2024.
The project was designed to improve safety and freight movement and replace aging, weight-restricted bridge infrastructure. All exits are moving to the right, and construction will eliminate blind merges.
Moving Coffee Creek was required, in part, because of the way the roadway above it is being configured for better driver safety.
The News Tribune asked the city engineer, Johnson, about the prospect of opening the creeks entirely. He described it as being too far-fetched for the current Twin Ports Interchange project, but not out of the question for another day.
"Miller Creek is an 1,800-foot-long tunnel (through lower Lincoln Park)," Johnson said. "The thought of opening up every road crossing and having to build a bridge would be tens of millions of dollars to do that. But it may happen someday. Lincoln Park has great energy right now. Someday there may be a great desire to do that."