How Minneapolis’ simple change to newly built boulevards will improve water quality
If you’ve walked along Grand Avenue in southern Minneapolis recently, you may have noticed a subtle change in the boulevards along the newly rebuilt street.
Instead of a continuous curb along the length of the grassy area that separates the street from the sidewalk, the boulevards have cutouts in the curb with special drains that will make the water from the street run out into the boulevard itself, instead of along the gutter to a storm drain.
The boulevard rain gardens – technically known as “bioretention areas” – are part of a city-wide effort to take a more environmentally friendly approach to managing rainwater runoff. In the two-mile stretch of Grand Avenue Reconstruction, which runs from Lake Street to 48th, the city has installed 126 of the boulevards’ rain gardens.
Rainwater runoff is easy to ignore in an urban environment. When everything works properly, it runs in storm drains and out of sight. But the water that can be polluted by everything from lawn fertilizer to car fluids needs to go somewhere. In Minneapolis, it flows into water bodies such as the lakes, Minnehaha Creek and the Mississippi River, where it can damage the aquatic ecosystem and cause excessive erosion.
The boulevard rain gardens are designed to reduce the flow of water to storm drains by absorbing some of the contaminated water in the soil, where it can be filtered by plants and soil and the water returned to the soil. Allison Bell, who oversees the projects as a green infrastructure coordinator between Minneapolis’ surface, water and sewer division and transportation, planning and programming team, compared the gardens to what would have happened naturally before the city was built. “The heart of green infrastructure is that it tries to emulate what happened before we evolved before we lay roads and houses and buildings,” Bell said. “Water, when it rained, would basically penetrate into the ground or go into rivers, lakes and streams without collecting a lot of pollutants that we have now introduced.”
For this purpose, the rain gardeners also make use of native plants. Since native plants are naturally adapted to the ecosystem of the area, they require less maintenance. As an added bonus, the plants fight weeds.
“They’re just more resilient,” Bell said. “And the reason they are is because they have these really deep root structures. So they seek water, and where there is peat in the ground, these go like feet, feet down into the ground.”
According to Bell, the bioretention pools along the Grand have already stopped nearly 500,000 gallons of water from entering the city’s storm drain.
Rain gardens are not the only green rainwater management technique used by the city. In some cases, crews build what are called “wooden graves” along roadways. Wooden ditches are more reminiscent of traditional boulevard plantings in that they have trees, but they also have curbs to allow rainwater to filter down into the boulevard soil. Wooden trenches were installed in Hoyer Heights in northeastern Minneapolis during road reconstruction last year.
MinnPost Photo by Tom Nehil
In the two-mile stretch of Grand Avenue Reconstruction, which runs from Lake Street to 48th, the city has installed 126 of the boulevards’ rain gardens.
Working the green projects into already planned road conversions helps lower the cost of the new infrastructure for the city. “They increase the size of the boulevard, they reduce the crossing distance for pedestrians, and all of this moves the curve a little closer together, giving us more space to work with,” Bell said. “We’re not talking about exorbitant costs. We usually just adapt what should already be there or in some cases, which makes it cheaper because we make native plants instead of concrete.”
Currently, Bell says the installation of rain gardens and wooden trenches is a “voluntary effort” by the city. But that will change next year when a new executive order requiring this form of rainwater management comes into force.
The new executive order means that Minneapolis residents can expect to see many more of these types of projects as roads are rebuilt in the coming years. Ongoing projects and the projects set up for the next six years are listed on a recently launched website of the department.
For residents who do not see a project in their neighborhood, Bell said the city is more than happy to guide them in creating their own rain gardens or tree pits. And while the city will not fund these projects due to budgetary constraints, Bell said they will make resources available to guide members of the community, including conducting design reviews.
“If a community wants to take on a project, if it’s something as simple as transforming their boulevards into sustainable landscapes, they can actually do it on their own, ”Bell said. “They do not need a permit. They can consult with landscape gardeners if they want to, or they can just do it as a joint event. We have seen successful programs with it.”
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