The Minnesota Department of Transportation (MnDOT) and general contractor S.M. Hentges & Sons are working on a project along Highway 93 near the small town of Henderson, Minnesota, about 60 miles southwest of Minneapolis. Although Highway 93 is just 5.6 miles long, the route is vital for Henderson since it connects to U.S. 169, a major north-south highway that runs from Minnesota to Oklahoma. The project will increase reliability and keep Highway 93 more consistently operational.
Henderson and Highway 93 are located in the vicinity of the Minnesota River and the Rush River, making flooding common in the area.
According to the MnDOT website, Highway 93 and Highway 19 in Henderson were flooded and closed for 61 days between March 16 and July 5, 2019. In 2020, there were five closures that lasted around 22 days. The website says that the closures “are often for multiple days and weeks at a time when flooding is caused by high waters of the Minnesota River. Closures occur more frequently, but for shorter durations, with flash flooding of the Rush River.”
Due to the flooding, MnDOT and the local towns conducted a feasibility study in the Minnesota River Valley to explore transportation improvements that would minimize closures. Ultimately, the decision was made to raise Highway 93 because it provides “the best benefit-cost ratio,” according to MnDOT.
The project involves a few key elements:
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- Reconstructing 3.6 miles of Highway 93 from Highway 169 to Elm Street
- Raising the Highway 93 roadway up to 8 feet (1 foot above historic high-water events)
- Replacing Rush River Bridge
- Constructing additional overflow bridge to allow for Rush River flood relief
The average daily traffic on two-lane Highway 93 is 2,200, with most traffic being local.
“This project was originally meant to be standard mill and overlay, but the state legislature secured funding to get it done sooner than initially projected,” MnDOT Construction Engineer Adrian Anderson said. “We knew something needed to be done because the Rush River lives up to its name, as it’s quick to rise and fall. The flooding is a yearly event and typically leads to closures for up to three weeks a year.”
The issue is complicated because Highway 19, which runs perpendicular to Highway 93, typically floods at the same time.
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There are only four ways into Henderson: from the south on Highway 93, from the east and west on Highway 19, and from the north on Sibley County Road 6. When coming from the west, travelers will encounter bluffs.
“When there’s a flood, there's often only one way in and out of town, and that's going up a bluff, which can add 20, 30 minutes onto people’s commute that is normally only 5 to 10 minutes [for those going south],” Anderson said.
There have been storms that impacted all four routes in and out of Henderson, leading some residents to use boats to get out of the community and take their children to school and buy groceries.
Due to the soil in the Rush River, the team needed to use unique drilled shaft foundations for the bridge. The drilled shafts are 6 feet in diameter and go down 98 feet.
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“We have to worry about scour on the drilled shafts, so we put a 40-foot-long protective sleeve on the shafts,” Anderson said.
As the team was preparing to drill down and lower the drilled shafts, they realized that the foundation footings of the previous bridge were larger (by about 2 feet) than shown on the as-built plan. The team is leaving the footings from the previous bridge in place.
“After about a week, the bridge office developed a redesign, and we were able to shift the drilled shafts over 1 foot each to avoid the conflict,” Anderson said.
As part of the project, the city of Henderson is getting a partial levee realignment, which was necessary to preserve several houses on the south side of town. The team has had to track surcharging and embankment placement across 19 separate sections of the roadway.
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“Some of the segments have multiple stages of surcharging or embankment placement, including one that we had 89 weeks of total settlement time,” Anderson said. “It's broken into two sections: get up to Stage 1 fill height, leave it for 60 weeks. And then once that's done, we can place the rest of it and wait another 29 weeks.”
Anderson added that this is the main driver of the schedule.
“If we stack the dirt too quickly, it can lead to instability and safety issues, so it was a lot of tracking,” he said.
Ultimately, the team only had to wait 54 weeks, rather than 60.
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Another challenge, Anderson noted, was working in the floodplain. Work has been halted due to flooding multiple times.
The bridges, which are just 1,000 feet apart, are relatively small. The Rush River Bridge is 197 feet, and the overflow bridge is 269 feet. The overflow bridge is on a section of Highway 93 that typically floods first.
Construction on the project began in the summer of 2024. Soon after the project began, the area experienced a historic flood event. It set a record for the city of Henderson's river gauge by over 1 foot, and floodwaters came within 1 foot of the top of the levee.
“It was the worst time we could have had a flooding event,” Anderson said. “We wondered how long we would need to be shut down, and it raised schedule concerns.”
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Ultimately, the project was shut down for six-plus weeks. Even after the floodwaters receded, the team was challenged by doing grading work in an area that had just flooded. Getting equipment to the area was difficult.
MnDOT and the general contractor, S.M. Hentges & Sons, held monthly meetings to review the overall schedule. For over a year and a half, the meetings focused on the schedule and the ways, if any, they could regain time. At this point, the team expects to complete the job in fall 2026. The original expected completion date was summer 2026.
S.M. Hentges & Sons is very familiar with the area, as their headquarters is about 20 miles northeast of Henderson. The contractor has partnered with MnDOT multiple times and completed many bridge and road projects in the vicinity of Henderson.
Anderson has a good working relationship with the contractor, which he said has benefitted the current project.
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“They've done a good job of proposing value engineering proposals,” Anderson said.
One such proposal was accepted, saving the department approximately $350,000. Anderson explained S.M. Hentges & Sons’ proposal below:
“Perimeter control of construction stormwater is a unique challenge on this project, as nearly the entire project is located right next to wetlands or environmentally sensitive areas,” he said. “So, we've got some pretty robust perimeter control in the form of 1 cubic yard sand totes, which helps ensure no embankment leaves the site and keeps floodwaters out.
“The sand totes are cumbersome to install. And, once you raise the road grade, the challenge is how to remove them. We were 40 feet away from where we placed them and 8 to 10 feet higher. Hentges proposed an alternative method that involved a concrete Jersey barrier wrapped in geotextile, known as Super-Duty Silt Fence, to replace the sand totes. The Super-Duty Silt Fence will be easier to remove in the locations it was emplaced.”
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The $32.5 million project is slightly over budget due to the design changes related to the issue noted above. Nearly $25 million was covered by bonding from the State of Minnesota, while the federal and local governments are also contributing. The city is paying for the levee portion.
When the project is complete, Henderson residents will experience more consistent access along Highway 93. The road will also have an improved pavement and safety. They can use their boats solely for fishing and other recreational activities, rather than for getting in and out of town, even during high-water events.
- Owner/Engineer: Minnesota Department of Transportation
- General Contractor: S.M. Hentges & Sons, Jordan, Minnesota
- Designer: Bolton & Menk, Mankato, Minnesota
