Minnesota Is Getting Wetter. Are Cities Ready?
The imperative to update stormwater infrastructure is urgent, and both private owners and public agencies have a lot at stake
By Jon Commers | September 21, 2023
The Minnehaha Creek Watershed District is working with Alatus, the City of Hopkins, and other partners on a transit-oriented housing development on Blake Road with stormwater as a centerpiece. Photo by Andy Clayton-King—Associated Press (AP).
DESIGN DATA
Minnesota’s 50 largest cities are all oriented to prominent bodies of water: Metropolitan cities emerged around the core of St. Paul and Minneapolis and the convergence of the Mississippi and Minnesota rivers. Duluth is inseparable from Lake Superior. And Rochester, Mankato, Moorhead, Owatonna, Austin, Winona, Faribault, and Farmington developed as river towns.
As a result, when we think of flood risk, most of us conjure images of volunteers filling and stacking sandbags along rivers. But stormwater has quietly assumed a much larger role in our urban life—in those parts of our cities nearest lakes and rivers, and those places more distant. Addressing the implications of and crafting responses to expanding inland flood risks will involve all of us—especially those designing city spaces.
Minnesota is getting wetter. Average annual precipitation has increased by 3.4 inches since 1895, a shift occurring at an accelerating rate. According to the Minnesota Department of Natural Resources, the state has experienced at least 11 “mega-rains” since 2000, defined as “events in which six inches of rain covers more than 1,000 square miles in 24 hours or less, with at least eight inches falling somewhere in that area.”
Emblems of these severe rain events include the 2012 flood in northeastern Minnesota. Over two days, 7.2 inches of rain fell in Duluth and up to 10 inches in surrounding areas, causing more than $100 million in damage to private property and public infrastructure. Five years earlier, a mega-rain delivered over 15 inches in southeastern Minnesota in the state’s largest recorded rain event. That episode triggered flash floods in communities including Rushford and Hokah, killing seven people and causing over $200 million in damage.
The Duluth and Rushford events are familiar to most of us. What may be surprising is the pace of change in stormwater conditions in Minnesota, and the rising stakes in designing places to accommodate increasing and more erratic volumes of stormwater. As annual rainfall increases and the frequency of large rain events grows, existing stormwater management systems are inadequate to stop flooding in inland areas. In Minnesota’s downtowns, neighborhoods, parks, commercial districts, and other areas, there is increasing risk to property, infrastructure, and safety. That the stakes are high isn’t news to state, regional, and local governments, where some leaders have made strides—even within regulatory structures and development timelines that can be slow to move.
The Duluth and Rushford events are familiar to most of us. What may be surprising is the pace of change in stormwater conditions in Minnesota, and the rising stakes in designing places to accommodate increasing and more erratic volumes of stormwater.
Development of Minnesota cities over the last 200 years followed patterns reflective of a drier climate with fewer extreme weather events. In older urban areas like the cities of St. Paul, Minneapolis, and Duluth, stormwater pipes are embedded in dense networks of underground infrastructure, which makes upgrading those pipes particularly challenging. Regulatory frameworks, like the updating of FEMA maps currently underway in Minnesota, are arduous to develop, slow to implement, and reflect current conditions but not changes anticipated in the immediate term and years to come. Responsibility for collection, retention, and management of stormwater often falls across multiple departments within local governments, magnifying the variation among cities, with some demonstrating dramatically stronger planning and response than others.
In Duluth, leaders have undertaken a transparent process to update FEMA local flood risk maps. In Shoreview, streets have been constructed with permeable materials, significantly reducing the need for curbs and stormwater infrastructure in the design. At the Metropolitan Council, planners have built a suite of Climate Vulnerability Assessment tools to support local innovation, including a localized flood map screening tool.
In what is likely to become a landmark case study, the Minnehaha Creek Watershed District has pioneered a path by acquiring land near the Blake Road light-rail station for the Green Line extension. Across a 16-acre site, the district is partnering with developers at Alatus, the City of Hopkins, and others to feature stormwater as a centerpiece in a transit-oriented development involving housing and green space. Minnesota’s watershed districts link across city and county boundaries to provide regulation and support innovative projects with grant funds.
Still, like so many pressing issues today, the implications are too broad and interdependent to anticipate that government agencies alone can fully meet the need for more robust and dynamic stormwater management practices. The most meaningful progress in this work in Minnesota has come about from state Minimum Impact Design Standards (MIDS), which require projects to capture and treat 1.1 inches of rainfall on impervious surfaces onsite. This change established a public-private cost-sharing system that increases predictability and reduces damage from extreme weather events. It also forms a framework for response to increasing precipitation in the future that aligns incentives for private and public parties involved in site development.
Building on new approaches is imperative. As elsewhere in the U.S., Minnesota weather events are triggering increases in insurance claims that carriers describe as unsustainable under the current system. Our past approach—to prioritize moving stormwater to the nearest riverway rather than retaining it onsite or nearby—is one cause of aquifer depletion that threatens Minnesota’s future. In designing urban space for the coming decades, architects, planners, developers, and public officials will need to develop and advocate for approaches to stormwater that are both more aggressive and more flexible.
Jon Commers’ urban analytics firm Visible City performed a scope of work for the Minnehaha Creek Watershed District in an early iteration of the Blake Road project mentioned in this article.
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