Sometimes a highway construction project does not go with the flow.

After a years-long study, the Connecticut Department of Transportation (CTDOT) has narrowed down the possible design options for a long-term overhaul of the congested, crash-prone interchange of Interstate 84 and Connecticut Highway 8 in Waterbury, known as the Mixmaster.

Both alternatives, the Modern Crossover Interchange and the Naugatuck River Shift, would involve unstacking a series of highway bridges, reducing the number of ramps and opening access to the river, among other changes, according to Jonathan Dean with CTDOT's Bureau of Engineering and Construction.

A key difference between the two options, which will now go through the environmental review process, is that one calls for the adjacent Naugatuck River to be moved eastward to create space for Conn. 8 to be unstacked and reconstructed on the river's west bank.

It would not be the first adjustment of the river: CTDOT officials said it was moved once before when the Mixmaster was first built in the 1960s.

What is the Process for Moving a River or Stream?

Kevin Carifa, the agency's director of environmental planning, told CT Insider for an Oct. 16 article that moving a river or stream involves building a new channel and redirecting the existing watercourse to the new one. The process, he added, is more common than some may think.

"It is typical for a transportation project to relocate a watercourse," he said.

One example, Carifa noted, was the realignment of sections of the Mad River and Beaver Pond Brook as part of a project several years ago to widen and straighten out a stretch of I-84 in Waterbury, not far from the Mixmaster.

"We put this river system into some really crazy configurations," he said. "That had to be done with a lot of hydraulic review."

Shifting the Naugatuck River would be a much larger effort, Carifa acknowledged, and CTDOT will not be able to say whether it is the best option until it is vetted through the National Environmental Policy Act process, which is expected to take two to four years.

And exactly how the river could be moved has yet to be determined.

Either the Naugatuck River Shift or Modern Crossover Interchange would cost an estimated $3 billion to $5 billion, in 2022 dollars. Dean said the river shift would be the "slightly more expensive" option.

Actual construction work to rebuild the interchange's core is not expected to begin for at least a decade, CT Insider learned.

During the environmental permitting process, Connecticut's transportation agency must show federal and state regulators how it will mitigate impacts to a natural resource like a watercourse, according to Carifa.

For the I-84 widening project in Waterbury, crews used sandbag cofferdams — or barriers — to isolate construction areas and prevent pollution in the river, he said. CTDOT also worked with the state's Department of Energy and Environmental Protection (DEEP) to install features for fish, including "root wads."

Carifa described root wads as tree trunks that are cut or salvaged from construction sites and placed in a river system.

"And essentially what they do is create habitat for the fish [to] go underneath, to have shading, have an area of refuge [and] to take breaks as they're meandering up [or down] the streams," he said.

At another Connecticut project — the replacement of a bridge over Strongs Brook in East Haddam — brook trout were physically moved from the stream.

"Before the contractor started work, (DEEP) came out and they did this technique called ‘electrofishing,'" Carifa said. "They shock the fish — it's safe, it doesn't kill the fish or anything like that. [Then] they collect and … move those fish out of the way so they're not impacted by the construction.

"The success story afterwards is that the site is definitely seeing some migration of the native brook trout back into the stream," he said.

The East Haddam project also involved a bypass pump system that took water from an area upstream of the construction site and discharged it downstream.

During the design process, CTDOT will specify which materials a contractor will use when reconstructing a watercourse, Carifa said. Rounded stones, for example, may be preferred over crushed rocks because they look more natural.

The goal is to not just recreate a stream but add improvements, he explained.

For instance, invasive vegetation could be replaced with native plants. An old dam could be removed to allow more fish passage upstream. Boulders could be placed in a stream to help create pools for fish or shelves could be built into the riverbank to provide shade.

"When it comes to relocating a river, we need to prove to the agencies that we're going to make a betterment," Carifa said.