Final stages of Greenway project involve unique work in Big Sioux River

This piece is sponsored by Lloyd Construction.

The steady flow and depth of the Big Sioux River through downtown Sioux Falls wouldn’t exist without a critical piece of infrastructure: the low-head dam.

“Without any low-head dam, the water level is down to a stream, a creek, in the downtown area,” said Josh Roozeboom, senior project manager for Lloyd Construction. “It’s the reason the river looks like it does downtown.”

Right now, however, the river’s appearance isn’t thanks to the existing dam, which is north of Sixth Street. Instead, Lloyd Construction is managing a temporary diversion dike that redirects the river while work continues on a new low-head dam.

“It’s definitely a first for us,” Roozeboom said. “Doing something like this dam project in the river, working on a lot of uneven bedrock and the design of the dam to make it all work while diverting the flow of the river is definitely an interesting project.”

Limoges Construction, the project’s concrete contractor, has played a key role in executing the complex build.

“They’ve done a really good job wrapping their heads around the best way to approach it to produce the right end product,” Roozeboom said.

At the same time, the construction team also built a coffer dam, allowing BNSF Railway to make critical repairs to the bridge pier that spans the river.

“This keeps the work area dry so they can work on bridge abutments that needed repair because they’re getting older,” Roozeboom said. “We built our coffer dam in a way that let us push the water over the completed portion of the new low-head dam and installed culverts over an access road so we could work from both sides of the river — because the river still has to have somewhere to go.”

That kind of coordination has minimized disruption, said Tory Miedema, park development specialist for the city of Sioux Falls.

“BNSF had this maintenance work to do, and for them to do it on their own, they would have had to go through the same permitting process we did with the U.S. Army Corps of Engineers and build roughly the same coffer dam,” Miedema said.

“This way, we’re only disrupting the river once instead of having to come back and tear up the park to get the work done. Plus, our new low-head dam could have gotten damaged. This way, by August, everything should be done, and the river should be back and flowing like it should.”

This type of work is rare, Miedema added.

“It’s a hard place to work, and before the River Greenway, we didn’t do much heavy construction along the river or in the floodway,” he said. “We do annual maintenance work, but that’s not the same as actual development, pouring concrete and installing permanent structures in the river.”

It also was time for the low-head dam to be replaced, he continued.

“It was over 100 years old. It was a historic structure, but it was deteriorating pretty fast,” Miedema said. “This keeps a consistent river level, and for more than a decade, we had seen it continuing to get lower and lower. We were starting to get some breaches, so we knew the time was coming for a replacement.”

When the River Greenway development moved forward from Sixth Street through The Steel District and Falls Park, the time was right to address the dam.

Lloyd Construction, which is overseeing the entire River Greenway project, completed part of the new low-head dam last fall and will finish the rest this year.

In the meantime, Lloyd Landing — a multiuse public space — was completed last year.

It features a shelter for picnics or gatherings, a multipurpose synthetic turf lawn, a small dog run, seating and a photo station. Plans also include public art and activities like outdoor fitness, food trucks and live music.

“All those improvements were completed up to the pedestrian bridge on the far north end, and that’s as far as it could go until we finish work on the dam and remove the temporary access road,” Roozeboom said.

“Then, we’ll make the final sidewalk and boardwalk connection to the work they’re wrapping up at Jacobson Plaza, and it will all tie into the sidewalks that go down to Falls Park and back up to Phillips Avenue.”

Repairs to the BNSF bridge are expected to be complete in May. Assuming no further delays, the full River Greenway project and new access to Falls Park via the boardwalk will be finished later this summer.

Interpretive panels also will be installed to share the story of the original century-old low-head dam that helped shape the modern look of the Big Sioux River downtown.

“The project has gone great,” Miedema said. “Lloyd actually opened a portion of it more than six months early, and they’ve been working quite a bit ahead of what we anticipated throughout, so as far as the construction, they’ve been doing a great job.”

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