Overgrown vacant lots and foreclosed homes — you know, those blighted bank-owned properties that serve as magnets for disease-carrying insects and/or indoor pot growers — are being considered in a handful of Midwestern cities as a means of protection against storm-related municipal sewer backups that wreak havoc upon happily occupied homes.

In attempt to improve its increasingly overwhelmed stormwater management system, the City of Milwaukee, a city that's no stranger to outside-the-box civic solutions, recently released a 20-page feasibility study revolving around the idea of converting the basements of long-abandoned homes into underground stormwater cisterns —"BaseTerns," if you will. Runoff from heavy rainstorms would be diverted to the holding tanks and be kept there until rains cease and the risk of sewer backups and localized flooding has passed. To be clear, any aboveground structures on the lots would be demolished; only the cellar-turned-cistern would be retained. Community gardens (irrigated with reclaimed rainwater, naturally) could potentially replace the razed homes making for an intriguing mash-up of urban agriculture, blight-remediation and stormwater management. 

As detailed by NPR, Milwaukee, like many other cities, has a combined sewer system that handles both domestic waste and storm runoff. During and after heavy rainstorms, basements are sometimes left with a particularly nasty remainder: a soupy and stinky mix of raw sewage and rainwater that bubbles up through floor drains when the system is overstressed.

Eric Shambarger, deputy director of Milwaukee’s Office of Environmental Sustainability, conceived The BaseTern concept after noticing that much of the city’s most severe basement flooding happens to occur in close proximity to a large number of foreclosed homes in a north-central section of the city. Many of these beyond-repair homes —"blighted houses that cannot be economically saved" — are in the process of being demolished by the city with plans to, among other things, transform the vacant lots into small-scale urban farms.

Shambarger explains to NPR: "If we are going to demolish the house anyway and there's going to be a vacant lot there, why not keep the basement portion of it? Let's get water into those basements, and in the process keep other basements dry. We are making good use of a hole in the ground that somebody put there for us."

In his introduction to the HTNB Corp-conducted "Vacant Basements for Stormwater Management Feasibility Study," Shambarger specifically mentions the flood-related damage resulting from potent storms that rocked the Milwaukee area in 2008, 2009 and 2010. In 2010 alone, the city’s call center fielded 11,600 reports of flooded basements. City officials are bracing themselves for even more sewage backups and stormwater-related headaches in the coming years: "… with climate change, extreme weather appears to be becoming a new normal for our region."

Shambarger adds in a Civil Engineering magazine article that profiles the project: "In general, the city’s sewer system works very well, but I think our combined sewer system is designed for what’s known as the 10-year storm or the 10-percent probability storm. We’re just concerned that the frequency of the intense rain events is increasing, and now we need new solutions to manage those major rain events."

(Illustration: City of Milwaukee)

At some point next year, the city will move ahead with a BaseTern pilot project in which a single, strategically located basement will be converted into a holding tank for storm runoff. Civil Engineering elaborates on the pilot project:

It plans to follow HNTB’s 'multipurpose' alternative for the project, which calls for using a series of rain barrels to capture runoff from nearby rooftops, allowing the overflow to go into the basement along with runoff from the street. Depending on whether stone or rainwater harvesting cells are used, the basement is expected to hold between 1,800 and 6,000 cu ft of water.

The walls of the test basement will be sprayed or lined with a waterproofing material to prevent the water from seeping through, while holes will be drilled into the floor so that some of the water can infiltrate the ground. A pipe attached to the basement’s existing floor drain will allow the remainder of the water to flow slowly into the sewer system, while the water in the rain barrels will be used to irrigate the garden. A single BaseTern project is expected to cost between $34,000 and $79,000, depending on the basement conversion method used.

And it would appear that Milwaukee isn't alone. Communities in and around Chicago have also started to embrace forsaken real estate as a means of preventing costly residential flood damage. As reported by Crain’s Chicago Business, a handful of abandoned homes in the city will soon be demolished (the basements, in this instance, will not be retained) to make way for full-on rain gardens that act as giant and super-absorbent sponges during heavy storms. Covered with native plants, the gardens soak up stormwater and prevent it from rushing into streets where it overwhelms sewer systems. Officials in Cleveland are also mulling over the possibility of using vacant lots to better deal with stormwater runoff.

Brent Denzin, an attorney with the South Suburban Land Bank and Development Authority located in the Chicago suburb of East Hazel Crest, explains to Crain's that the vacant lots-turned-rain gardens are in flood-prone areas: "We're not talking about properties with a major resale value. You look at the value of that parcel (and figure out) whether it's more valuable to be rebuilt as a home and sold, or whether it will save the county money over time because they're strategically addressing a stormwater problem."

Via [NPR], [ASCE] via [Gizmodo], [Crain's]

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Matt Hickman ( @mattyhick ) writes about design, architecture and the intersection between the natural world and the built environment.

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