Engineers grapple with how to build climate resilience into Michigan’s stormwater infrastructure

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Local municipal water engineers are in a tough spot these days. Bound by often-outdated county and municipal drainage codes while managing aging infrastructure, there’s only so much they can do when planning for a warmer, wetter future in Michigan.

“I think many municipal engineers, especially those responsible for stormwater systems, are probably quietly panicking a little bit right now,” said Ric Lawson, a watershed planner with the Huron River Watershed Council. “They’re just waiting, knowing that a big storm around the corner will blow everything up, cause a big flood or basement floods, whatever. And that fingers may be pointing back to aging infrastructure and what they haven’t done to maintain that.”

Metro Detroit and the rest of the country face a changing rainfall regime, with storms increasing in intensity and duration. The region’s aging stormwater infrastructure will be called on to deal with more rainfall. We’re likely to see more catastrophic floods in low-lying places like river corridors. In areas with combined sewers like Detroit, we’re more likely to see basement backups like those experienced in June of 2021.

Source: Southeast Michigan Council of Governments

The past can’t predict the future

Stormwater engineers are limited by local drainage ordinances that prescribe how large pipes must be to handle increasing stormwater volumes and how much rainfall should be retained on site. Those local codes draw from the American Society of Civil Engineers (ASCE) standards based on historical rainfall patterns.

That means that local engineers typically look at what rainfall has been like in recent decades when designing stormwater systems, not what it’s like now or is likely to be in the future. And, Lawson said, requiring developers to exceed those standards could leave municipalities open to lawsuits.

Some municipalities avoid liability by building safety margins into their designs. “Instead of saying, ‘Well, we’re going to use larger rainfall numbers,’ they build in a margin of safety that is trying to account for the fact that we know that we’re using old, historical storm figures and that the actual storms that these systems are going to take on are going to be much bigger,” Lawson said.

But a better approach is needed, according to Dan Walker, a vice-chair of the ASCE Committee on Adaptation to Changing Climate and chair of the ASCE Committee on Climate Intelligence for Codes and Standards.

“It’s widely acknowledged that most codes and standards for guidance documents for engineering design were written at a time before an understanding of how changes in weather and climate extremes are being driven by climate change,” Walker said.

In practice, this means stormwater engineers may be designing pipes for a 1980-rainfall world when they should be thinking about what rainfall will look like in 2050.

“If we’ve used 40 years of data to define what we think will be the maximum flood or maximum precipitation in engineering design, that’s not a valid assumption because the climate is changing. You can’t use the last 40 years to predict the next four years. And that’s the biggest challenge because the vast majority of practicing engineers are not taught that in school.”

Most municipal engineers rely on NOAA Atlas 14, which describes precipitation distribution, to design and size stormwater systems. “But that product is historically based. And it doesn’t account for climate change,” Walker said.

Walker is working with ASCE and the National Oceanic and Atmospheric Administration (NOAA) to address ways to serve engineers’ information better needs when it comes to weather and climate while updating ASCE standards to be more sensitive to climate change.

In the absence of a systematic effort at the federal level, local municipalities and regions have begun to develop their own techniques for predicting rainfall. In Michigan, the City of Ann Arbor has developed a stormwater model that allows city planners to enter various rainfall scenarios to identify where the city should invest in upgrading infrastructure and increasing rainfall storage capacity. But Walker believes a comprehensive effort on the federal level is needed.

“Local communities get together and find resources to try to solve the problem on their own, and that’s inefficient,” Walker said. “And it makes it difficult for engineering firms working in different regions because they have different guidelines to follow.”

It also creates an environmental justice issue because wealthier areas have more resources to develop models for predicting future rainfall than poorer ones, Walker said. Places like Seattle, New York City, and Miami Dade County can afford to create their own standards, “but if you’re in rural Mississippi or some of the Midwestern states where their economic base isn’t the same as it used to be, you’re kind of on your own. And so the idea is if you have a federal effort, and there’s more consistency, then underrepresented, underserved communities can get the same level of information as a wealthy community.”

Regional collaboration needed

Kelly Karll is the manager for environment and infrastructure at the Southeast Michigan Council of Governments (SEMCOG). She’s been working to publish future rainfall predictions for mid-century and end-of-century for the SEMCOG region to help local municipalities and engineers prepare for what’s coming and disseminate guidance and recommendations for engineers.

“We need to work more collaboratively to determine what this means for engineering and infrastructure planning and design,” Karll said. “How do we incorporate increasing rain events into our planning and design?”

To that end, Karll is coordinating a SEMCOG Water Infrastructure Task Force to focus on “short and long-term actions needed for sustainable water infrastructure systems in Southeast Michigan.” The group will prepare a supplement to the region’s 2018 Water Resources Plan for Southeast Michigan, including recommendations for needed regulatory and legislative reforms, investment priorities, asset management protocols, and ways to build public confidence.

“Changing how we do business is a process. And we’re at a time where we need to do that,” Karll said.” But also, we can’t just make quick decisions on this. We need to know what best practices are and what works.”

Lawson would like to see more municipalities follow the lead of Washtenaw County and the City of Ann Arbor, which have required onsite infiltration of stormwater into their standards for six years. Macomb, Oakland, and Wayne counties have recently updated their stormwater standards to include infiltration to comply with federal requirements. But Lawson said those standards are not as aggressive as what he’d like to see, and what Washtenaw County requires.

“More storage and infiltration will go far as long as you’ve got groundwater that can accept it,” he said, noting that places at lower elevations with higher groundwater tables, such as those found in the Detroit area, may limit the amount of infiltration possible. He said that using green infrastructure like bioswales and rain gardens to infiltrate stormwater may be more of a challenge in these areas.

“Green stormwater infrastructure, from our perspective at the Watershed Council, is great – we want as much of that as we can get,” Lawson said. “But there’s also a need for gray infrastructure in the older, built-out parts of the watershed, which is certainly true the closer you get to Detroit.”

And Lawson said that while it’s theoretically possible for green infrastructure to help fix Detroit’s basement flooding problem, it “has to be done on such a large scale because so much of the area has been built out without any stormwater infrastructure – and it’s hard to get it done at scale.”

Funding future resilience

Most municipalities in Michigan don’t have a specific source of funds to pay for stormwater infrastructure outside of general funds.

“For water utilities and wastewater systems, you have utilities in place to collect the revenues to take care of those. For stormwater, most municipalities don’t have that,” Lawson said.

Two exceptions include the Detroit Water and Sewer Department and the City of Ann Arbor, which have implemented drainage fees and credits systems to fund stormwater operations. Michigan’s narrow definition of a utility has caused reluctance among many water infrastructure managers and municipalities to adopt such a funding strategy. A 1998 Michigan Supreme Court Case, Bolt v. City of Lansing, found that Lansing’s stormwater charges were invalid. That’s had a chilling effect on Michigan’s broader adoption of stormwater utilities. That may only change with the adoption of enabling legislation, something Lawson said has not been successful.

The Clean Water State Revolving Fund, a low-interest loan program, is the primary source for stormwater improvement. The upcoming federal Infrastructure Investment & Jobs Act will funnel an additional $115 million for water infrastructure through this fund.

Lawson also points to the state’s Stormwater, Asset Management, and Wastewater (SAW) Program, a grant program for municipalities that funds stormwater and wastewater systems asset management. The program allows cities to identify where investment in projects to upsize pipes and put in detention are needed.

“Because there are a lot of communities that didn’t know the status of their stormwater infrastructure, you know, how old the pipes were, what kind of shape they were in,” Lawson said.

Other small grants and programs at the state and federal level are not enough to fill the gap, according to SEMCOG, which estimates a third of the region’s water infrastructure is in poor condition, with $3.5 billion needed annually to keep drinking water, wastewater, and stormwater pipes to good or fair condition, not including costs for wastewater treatment plants and flood control.

And that’s to keep up with the status quo. “For storm sewers, if we’re looking at potentially upsizing, you could add another couple billion. Our regional investment needs are really on the order of about $5 billion annually.” Karll said.


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