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By Dan Gunderson

Moorhead officials are preparing for a changing climate and the extreme weather more likely in the future.

Moorhead will benefit from the $3 billion Red River flood diversion project expected to be complete in 2027. The diversion will eliminate the risk of river flooding.

But the project won’t protect the city from extreme rain events, now more common because of climate change.

“What we generally will see is the storm sewer system is overwhelmed by intense rain events, events that are larger than the size they were designed to handle, and water will pool in the street,” said city engineer Bob Zimmerman.

Temporary street flooding is an inconvenience said Zimmerman, but when the water floods homes or businesses, disruption and cost can be significant.

Using grant funding from the Minnesota Pollution Control Agency, Moorhead created a detailed storm water management plan.

The geography of the Red River Valley adds a challenge. Heavy clay soils limit how much rainfall sinks into the ground, making rain gardens or green spaces less effective. And the land the city is built on is very flat.

“Typically, storm sewers drain by gravity,” explained Zimmerman. “And in this part of the world, if we tried to design storm sewers for huge events, extreme events, the size of the pipes would be so large, the cost of the development would be so large, that essentially it would be not economical for the city to grow.”

The city plan calls for strategic storm sewer upgrades combined with temporary rainwater storage.

Zimmerman said some storm sewers are more than 70 years old and necessary upgrades would cost about $120 million, including the cost of rebuilding streets.

The city unsuccessfully applied for federal funding to start the work. Zimmerman says it often takes years to get federal or state funds for infrastructure projects.

Borrowing for construction would double the monthly storm water fee for residents. There’s also the unpopular option of special assessments on property.

“That’s a tool in the toolbox we could use,” said Zimmerman, “But definitely one that we would prefer not to.”

Moorhead is an early adopter in climate planning. A 2022 survey of 380 Minnesota local governments found only 12 percent had a standalone climate resilience plan.

But nearly 90 percent said they have experienced the effects of climate change with extreme rain events or drought.

The MPCA offered another round of planning grants this year and also made $35 million in grants available to help upgrade aging stormwater systems.

MPCA climate director Kate Knuth knows that is a small down payment on the statewide cost of climate change mitigation. She said the state is committed to making significant investments in climate resilience over the next decade, but the state doesn’t yet know what the total cost will be.

“One flood mitigation project isn’t exactly the same in Duluth versus Moorhead versus Mankato,” she said, “So this is an ongoing part of the work we’re doing.”

Knuth said it’s clear the state needs to invest in infrastructure to help cities mitigate flooding and other impacts of extreme weather events.

“When we plan for and build infrastructure and other projects that help communities prepare for climate impacts we’re going to see benefits,” said Knuth. “Not just for six months or a year, but over decades.”

The state is also developing metrics to measure the return on investment when infrastructure upgrades prevent floods.

That can be complicated.

“Measuring resilience is not only about the numbers, but it’s really about the impacts that we see on the ground, or those that maybe we don’t even see,” said University of Minnesota Climate Adaptation Partnership associate director Amanda Farris.

For example, it’s difficult to quantify the cost of a flood prevented by infrastructure improvements.

Farris said Minnesota is among a handful of states that are creating ways to measure the investment in climate resilience.

Measuring resilience will evolve as more projects are built and more data is collected, she said. Farris believes it’s critical to not just measure the end results, but to give local governments a way to measure progress on what might be a long slog.

“Then they’re working to collect that data and information along the way, and they’re also planning in a way that they can go back to the plan as they implement, and think about the progress that they’ve made, think about maybe where they want to adjust their investments, where they’ve been successful,” she said.

Moorhead engineer Bob Zimmerman ponders what climate change means for the future and how to best decide what size stormwater pipes to put under the street. That planning process is being turned upside down by climate change.

“Historically, storm sewers have been sized based on standards that look at previous rainfall events and then tell us based on that previous data, that a 100 year event might be 6.5 inches in a day,” he explained. “The hard part is to project what climate change means for that number.”

There are projections for what climate change might mean at the county level in Minnesota, but for an engineer, projections are less reassuring than hard data.

Moorhead is beginning to change how it does infrastructure projects. The city currently replaces streets based on pavement age and condition. Zimmerman expects in the near future the age and size of stormwater pipes under the street will become part of that decision.

But the city will still need to find a source of funding to replace those aging pipes.