Type: Capital Improvement Project
MWMO Funding: $295,000 Capital, $75,000 Engineering
The MWMO and its partners are implementing a pilot project to introduce green infrastructure into downtown Minneapolis street design. One block of South 8th Street will be reconstructed with stormwater planters that will infiltrate polluted runoff and provide greening in a busy downtown corridor. Once completed, the MWMO will monitor infiltration and vegetation growth in the planters to evaluate their effectiveness.
MWMO staff spent several years working with the City of Minneapolis and the Downtown Improvement District (DID) to identify opportunities to install green infrastructure on downtown city streets. After evaluating several potential projects, the partners chose the South 8th Street reconstruction to serve as a pilot. The city planned to reduce the width of the vehicle lanes and widen the sidewalks, pulling the curb-line out into the roadway and minimizing utility conflicts. This made it possible to install stormwater planters without impacting pedestrian needs.
The infrastructure will be located in city right-of-way (just behind the curb-line), and will capture and treat runoff from the street. The design calls for five stormwater planters — large bioinfiltration basins with recessed soils to allow space for stormwater to pond before it infiltrates. Each of the planters will contain trees and sedges, which assist with infiltration and treatment of the stormwater that drains into them. The planters will capture and treat runoff from South 8th Street from 5th to Portland Avenues, along with the alleys and sidewalks that drain to it. Initial estimates are that we’ll remove more than 200 pounds of total suspended solids and one pound of total phosphorus each year. The modular design allows for easy replication in other areas, if those opportunities arise.
The project will help further DID’s goal of adding green spaces downtown to soften its largely hardscape environment, promote wayfinding, and make the streets feel more human in scale. One of the ways this project helps accomplish that goal is by planting trees in large “planters” rather than a more traditional 5-foot-by-5-foot opening in the sidewalk. This also matches up with Minneapolis Park and Recreation Board Forestry Department’s goals of helping provide better soils (and more of them) in order to grow larger, healthier trees.
The stormwater planters will be supplemental to the street stormwater infrastructure, capturing street and boulevard runoff in catch basins to remove sediment and debris. From there, pipes move water into the planters, which are structured with galvanized steel frames with an open bottom, allowing the trees and the water to take advantage of additional space outside of the planters themselves. The MWMO will monitor the stormwater infiltration at each of the five planters, observe vegetation growth, and use information gathered to inform future similar projects.