Flooding in the Minnesota River Valley has created maintenance and mobility challenges for MnDOT and local communities for decades. The city of Henderson has been hit especially hard in recent years with area road closures reaching an all-time high. In 2019, both Hwy 93 and Hwy 19, two main routes into Henderson, were closed for a total of 61 days between March 16 and July 5. In 2020 there were five closures for approximately 22 days. 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.
In 2017, MnDOT partnered with local communities including the City of Henderson, Sibley County, Scott County, and Le Sueur County to conduct a Flood Feasibility Study to investigate transportation improvements in the Minnesota River Valley that would minimize closures due to flood events. The study focused on three alternatives: raising either Hwy 19 or Hwy 93 or County Road 6 above the 100-year flood elevation.
Of the three alternatives, raising Hwy 93 provides the best benefit-cost ratio. The cost to raise Hwy 93 was estimated at $14 million (2017 dollars). When adjusted for estimated inflation and additional flood mitigation measures for the Rush River, the cost is estimate to be $24.8 million (2023 dollars).
Because a grade raise of Hwy 93 for flood mitigation couldn’t be supported by MnDOT south central district’s annual program allocations, the City of Henderson pursued funding from the state legislature. In October 2020, a bonding bill was passed for transportation infrastructure, with Henderson flood mitigation as a part of it. With $24.8 million secured through the bonding bill, MnDOT is moving forward with a two-year flood mitigation project (2023-24) to raise Hwy 93 approximately 8 feet, putting it one foot above historic high-water events.