Madison, Wisconsin: A City of (Rain) Gardens
Last Friday I, along with about a dozen others affiliated with The Nelson Institute for Environmental Studies at the University of Wisconsin-Madison, was treated to a tour of some of Madison’s stormwater control projects, hosted by Greg Fries, the principle engineer for the City of Madison’s Storm and Sanitary Sewer Section. I’ve seen a lot of rain gardens in my day, but I was especially interested in hearing from Greg and seeing Madison’s projects.
For me, one of the most interesting aspects of our tour was to see stormwater management through the eyes of a city that takes it seriously. Madison is surrounded by freshwater lakes that, like so many others, have been plagued by excessive phosphorus and the resulting cyanobacteria (“toxic algae”) blooms. Whereas a city like Milwaukee, which still has a combined sewer, looks to rain gardens and green infrastructure primarily to decrease stormwater volumes, Madison, which has a separated sewer, is primarily focused on infiltrating stormwater into the ground where it can be naturally scrubbed of phosphorus and other pollutants before entering area streams and lakes.
The city started building rain gardens well over a decade ago and has taken pains to document its costs, techniques and results. Greg told us that, early on, the incremental cost of building a rain garden in the public right-of-way along the edge of a city street was about $20,000. Much of this cost was attributed to the hugely time-intensive effort of working with community members to explain the project’s goals, allowing them to have input into the design, and listening to their concerns. In addition, because they were new at the business of designing, building and maintaining the gardens, the first attempts were over-designed, with redundancies that added to the cost.
Today the process is much simpler, and is only a tiny fraction of that initial cost. When the city is ready to install a rain garden, it simply sends the adjacent homeowner a letter alerting them to the upcoming construction and asking them to select from a template of styles. Rather than having to convince homeowners to accept a rain garden, Greg now has the opposite challenge: Homeowners are calling his office wanting to know when they’ll be getting “their” rain garden.
I was especially excited to learn that Madison’s stormwater team has made it a practice to work closely with their colleagues who have responsibility for streets. Rather than have separate planning and construction processes, Greg’s team studies the city’s list of streets that are scheduled for reconstruction and focuses their rain garden installations on those streets. By piggy-backing on the street work and merging the construction contracts, the city saves valuable time and money. This is the exact recommendation that I’ve been hearing for years and years, but very few cities actually put this simple step into action. It allows them to move much faster, and in fact this small city now has hundreds of rain gardens in place.
Greg also shared with us a USGS study published in 2010 based on Madison rain gardens. The study was designed to put some solid data behind the twin questions of whether species composition matters, and whether soil type matters in rain garden design. You can read the study for yourself, but the answer boils down to “yes.” Having porous soils that include ample sand increases infiltration rates over those that have an impeding clay layer. That’s probably not very surprising, but it’s good to have data. They also showed that native prairie plants, with their deep roots, doubled or even quadrupled the water infiltration rates compared with gardens planted in turf grass. Root structure really does make a difference. Turf grasses have fairly shallow roots; examination showed that their roots did not go through the clay layer. Native prairie species, on the other hand, had deep roots that grew straight through the clay, creating micro-channels for water to seep through. And, of course, they are much prettier than turf!
Never ones to rest, Madison is now teaming up with USGS to study leaf management. When leaves fall into the street or, heaven forbid, are raked into the street, fall rains leach phosphorus from the leaves and carry it along to the storm drain and straight to the lakes. They are testing a wide variety of methods to see which will work best for keeping phosphorus in the ground and out of the water. I’ll have to check back in a year or two to see what they’ve learned!
This is my final blog posting on The Johnson Foundation’s site, under the banner of “On the Waterfront.” However, you can join me over at Broadview Collaborative, Inc where I will continue blogging on the sustainability questions on the top of my mind. After a brief hiatus my next post will be on a 2MW biogas facility that is being privately operated right in the heart of Milwaukee. I hope to you’ll stay in touch!