Type: Capital Project
MWMO Funding: $408,582
The City of Minneapolis is installing a series of stormwater-absorbing tree trenches along portions of Fillmore Street NE, Buchanan Street NE, and Lincoln St NE (south of 37th Ave NE) in Hoyer Heights as part of a street reconstruction project. This pilot project, supported by a $408,582 grant from the MWMO and a $113,459 Minnesota Clean Water Fund grant through the Board of Water and Soil Resources, will be among the first in the city to capture and treat runoff directly from the street in a residential neighborhood using a type of stormwater best management practice (BMP) called a tree trench.
The project was planned by the Northeast Stormwater Management Initiative, which seeks to improve water quality and flood resiliency in Columbia Park (including Columbia Golf Course) and the surrounding neighborhoods. Hoyer Heights was identified as an area that would benefit from flood mitigation measures, with stormwater modeling suggesting that street flooding will occur in a two-year storm or greater. Hoyer Heights also lies within a watershed that receives very little water quality treatment prior to discharge to the Mississippi River. The MWMO and the City of Minneapolis saw the opportunity for a project partnership, in that the city had been planning to reconstruct the streets and replace the sanitary sewer lines in the Hoyer Heights area (part of the Waite Park neighborhood) in 2020. Three of the streets, which are currently wider than typical residential streets, were slated to be narrowed for traffic-calming purposes. This provided an ideal opportunity to install new stormwater BMPs in the expanded boulevard space.
Design plans include curb cuts with pretreatment structures that will allow stormwater runoff to feed directly from the street into the tree trenches, which then absorb water and filter out pollutants. A variety of native deciduous trees, grasses, sedges, and flowering plants will be installed in the trenches, which have about 4.5 feet of soil media for stormwater to filter through. If there is more runoff than the trees and plants can use, the excess will flow into an 8-inch perforated PVC drain pipe, which is surrounded by stone to prevent clogging, at the bottom of the soil media. The deep-rooted plants selected for this project will provide excellent food and habitat for pollinators and other wildlife. The project will also help the city and the MWMO evaluate the effectiveness of tree trenches as a stormwater BMP, assess their maintenance needs, and determine their life cycle costs. In urban settings, trees are often put in spaces that are too small or don’t receive enough water; this stormwater BMP project will give trees a better chance at reaching maturity and provide important co-benefits like shade, carbon storage, improved aesthetics, and energy absorption. Construction of the tree trenches began in July 2020.
The city held three open-house meetings regarding the project, contacted the individual homeowners on the streets where the tree trenches will be constructed, and applied their input in selecting planting schemes. The property owners will be responsible for regular maintenance, such as watering after establishment during drought conditions, pruning, mowing or cutting back (typically no more than once or twice per season), and removing any accumulated sediment. MWMO staff will help conduct education and outreach to help residents learn how to monitor and care for the tree trenches. Minneapolis Public Works will inspect the BMPs on average once a year and remove large accumulations of sediment, inspect underdrains, replace plants, and perform any necessary repairs.