Moorhead officials are preparing for climate change and more likely extreme weather events in the future.

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

But the project will not protect the city from extreme rainfall, which is now occurring more frequently due to climate change.

“We will generally find that the storm sewer system is overloaded during heavy rains, that is, rainfall that is greater than the amount of rain it is designed to handle, and that water collects on the streets,” said city engineer Bob Zimmerman.

While temporary flooding of streets is a nuisance, if homes or businesses are under water, the disruption and costs can be significant, Zimmerman said.

With the help of grants from the Minnesota Pollution Control Agency, Moorhead developed a detailed stormwater management plan.

The geography of the Red River Valley presents an additional challenge. Heavy clay soils limit the amount of rain that infiltrates into the ground, making rain gardens or green spaces less effective. And the land on which the city is built is very flat.

“Typically, storm drains drain by gravity,” Zimmerman explained. “If we were to design storm drains in this part of the world for major events, extreme events, the pipes would be so big and the cost of expansion would be so high that it would basically be uneconomical for urban growth.”

The city’s plan calls for strategic storm sewer improvements combined with temporary stormwater storage.

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

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

Borrowing for the construction would double the monthly stormwater fees for residents. There is also the unpopular option of levying special taxes on properties.

“It’s a tool in our toolbox that we could use,” Zimmerman said, “but definitely one that we’d rather not use.”

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

However, almost 90 percent of respondents said they had experienced the effects of climate change in the form of extreme rainfall or droughts.

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

Kate Knuth, MPCA’s climate director, knows that’s just a small down payment on the statewide cost of mitigating climate change. 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 would be.

“A flood control project is not exactly the same in Duluth as it is in Moorhead and Mankato,” she said. “So this is an ongoing part of our work.”

According to Knuth, it is clear that the state must invest in infrastructure to help cities mitigate flooding and other impacts of extreme weather events.

“If we plan and build infrastructure and other projects that help communities prepare for the impacts of climate change, we will see benefits,” Knuth said. “Not just for six months or a year, but for decades.”

The government is also developing metrics to measure the return on investment when infrastructure improvements prevent flooding.

This can be complicated.

“Measuring resilience is not just about numbers, but also about the impacts we see on the ground, or maybe not see at all,” says Amanda Farris, deputy director of the Climate Adaptation Partnership at the University of Minnesota.

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

Farris said Minnesota is one of the few states developing ways to measure investments in climate resilience.

Measuring resilience will evolve as more projects are undertaken and more data is collected, she said. Farris believes it’s critical to not only measure end results, but to give local governments a way to measure progress in what could be a long struggle.

“Then they work to collect that data and information over time, and they also plan in such a way that as they’re implementing, they can go back to the plan and reflect on the progress they’ve made. They may consider where they want to adjust their investments, where they’ve been successful,” she said.

Moorhead engineer Bob Zimmerman thinks about what climate change means for the future and how best to decide what size stormwater pipes to put under the street. That planning process is being turned on its head by climate change.

“In the past, storm drains have been sized using standards that take into account past rainfall and then based on that data, tell us that a 100-year event could be 6.5 inches per day,” he explained. “The difficult part is estimating what climate change means for that number.”

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

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

However, the city still needs to find a source of funding to replace the aging pipes.