Central Corridor project offers chance for 'green' stormwater management

The coming of the Central Corridor light-rail line linking the Twin Cities' two downtowns is providing a unique look at the often overlooked issue of stormwater management.

The challenge for urban planners will be to take advantage of the burst of redevelopment along the rail line — to be known as the Green Line — to promote so-called "green infrastructure," which seeks to reduce the volume of polluted stormwater runoff into the Mississippi River.

One such effort nearing completion is the Central Corridor Stormwater and Green Infrastructure Planning Project, commissioned last year by the Corridors of Opportunity. The Metropolitan Council is spearheading the initiative and the St. Paul and McKnight foundations are providing the funding.

The project's goal is to establish a method of stormwater management in which separate property owners clustered around a transit node could join a common system using green, above-ground systems rather than building traditional individual underground holding tanks.

The above-ground techniques, such as rain gardens, catch basins and tree-filled infiltration trenches, are used to filter out polluting nutrients, bacteria and sediment from the runoff, as well as cutting its volume.

Under the shared stormwater concept, developers would benefit by not having to solely shoulder the financial burden of building their own management systems, while cities would benefit from the creation of new green spaces that fit their livability goals.

Led by the city of St. Paul and carried out by the Minneapolis-based SRF Consulting Group, the Central Corridor study — expected to be completed next month — got an "advance screening" for an audience of water resources professionals Tuesday at a University of ­Minnesota conference.

The big problem with trying to create above-ground stormwater systems is the lack of space for individual property owners to do so, Giese said.

"So we asked what if instead of every parcel doing their own stormwater management on their own property, is there a chance for adjacent parcels to share facilities? And further, could the stormwater that we're capturing be used to create a shared amenity?"

To help answer those questions, the study team focused on two redevelopment efforts along the Central Corridor — a planned 200- to 250-unit multifamily housing project from the Cornerstone Group near the Prospect Park station in southeast Minneapolis and the Curfew Commons site in St. Paul near the Westgate Station at University Avenue just west of Hwy. 280.

The centerpiece of the Cornerstone proposal would be the transformation of a two-block stretch of 4th Street SE. into "Green Fourth," a tree-lined corridor that would integrate stormwater management, urban gardens, pervious pavers, and pedestrian and bicycle uses, while still allowing for some vehicular traffic.

Cornerstone President Colleen Carey said in January that she was "excited about the potential pilot project for Green Fourth," and adding that it could demonstrate how "vibrant a street can be" by using rain gardens and urban agriculture.

In that scenario, untreated stormwater would be brought to the surface and held in bio-retention basins and a "great lawn," where it would be re-used and filtered by vegetation. Its landscaping would feature passive open spaces dotted with trails and public art.

"The concept addresses the need to infiltrate and re-use water where possible," Filipiak said. "We found that the system would re-use about 40 percent of the water that showed up at the site."