As more and more cities across the nation struggle with water runoff management, Portland Oregon is taking steps toward a long term sustainable solution. This ‘Green Infrastructure’ is not only a financially responsible solution, saving the city millions of dollars in the past two decades, but it also prevents much of the pollutants in the city’s water runoff from ever reaching nearby streams.
Introducing: Bioswales If you’ve been outside in Portland recently, you may have noticed unusual concrete structures sunk in to the sidewalks, outside LEED buildings downtown, or in newly constructed areas. These are bioswales, part of a country-wide effort to implement green infrastructure. The EPA defines “Green infrastructure [as using] vegetation, soils, and natural processes to manage water and create healthier urban environments”.[i]
Portland’s implementation of bioswales throughout the city were in large part a response to the 1.4 billion dollar “Big Pipe” constructed in 2011, a project which was intended to more effectively manage ground water and sewage. The main function of a bioswale is to reduce the amount of water runoff that reaches storm-water pipes. This is achieved by placing a trench filled with vegetation and soil next to concrete sidewalks and other impervious surfaces. This way, rather than sending water runoff into sewer pipes or directly in to the river, much of this water can be absorbed in to the bioswales. Every year, almost 4 million gallons of water are removed from Portland’s storm water system. An additional function of this infrastructure is to filter out water pollutants before they reach streams and rivers, and also reduce thermal pollution (water that is too warm to be healthy for our water sources).[ii]
The Impervious Problem Rainfall can either hit a pervious or an impervious surface on the ground. Pervious surfaces are those that act like the natural environment. They let rainwater through to the groundwater as it would if there were no manmade structure. Conversely, impervious surfaces are those that let no water through, but the water needs to go somewhere. Every year, billions of gallons of water strikes these impervious surfaces and run into pipes that take it to Portland’s water plants. At this point in time, Portland’s water practices dictate that any new construction with more than 500 square feet of impervious surface must have some way to manage storm water on site (such as bioswales).[iii] The goal is to reduce the amount of water that runs directly from impervious surfaces, heating up and collecting pollutants along the way, into our streams.
The Real Cost of Going Green Opponents of the bioswale movement often cite their high cost as a reason not to build them. While the cost of adding a bioswale ranges from $3-10 per square foot, the cost benefit of using a bioswale as opposed to the sewer system allows them to pay for themselves. With any commercial or private space, a major cost of ownership is water runoff management. In normal construction, this includes things like manhole covers and water pipes that run into the city’s water runoff system. With bioswales, however, this cost is reduced dramatically because in most cases a large amount of water is treated and managed within the bioswale itself with very little overflow ever reaching the water runoff system. An example of this is when OMSI renovated their parking lots in 1991, their goal was to manage 100% of water runoff on-site. All of the water is filtered in the bioswale and then sinks in to the groundwater. Only during heavy storms does water overflow and go in to the Willamette. In building costs alone, $78,000 was saved implementing bioswales versus a traditional water management system.[iv]
Conclusion The positive effects of bioswales aren’t limited to environmental benefits. They also improve the health and safety of Portland citizens. Streets that include bioswales between a sidewalk and the roadway are an improved street design for pedestrians.[v] Health and Community Design says that streets can have two purposes, one “to move people and goods between destinations”, and two “to serve as a stage for social interaction in a public setting”. Bioswales help shift the focus of streets from cars to the pedestrians that walk along them, by separating pedestrians from the flow of traffic. This certainly has a positive effect on the overall health of the community. Imagine a Portland where every drop of rainwater travels through a natural filtration system before going into our waterways. This is exactly what bioswales have to offer. They make fiscal sense for the city and its residents, because they cost less than big-budget projects like the Big Pipe to implement and cut down on water management costs. If every new private and commercial property being built also had storm water management built along with it, we would never have to worry about the environmental cost of water runoff. Bioswales are the most sensible solution fiscally and environmentally. As Portlanders it makes sense to take care of the place we live.
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Sources: [i] “What Is Green Infrastructure?” EPA.gov. Web. 17 May 2014.
[ii] “Watershed Friendly Landscaping: Bioswales.” Upper Des Plaines River Ecosystem Partnership. Web. 17 May 2014.
[iii] “2014 Stormwater Management Manual.” PortlandOregon.gov. 2014. Web. 17 May 2014.
[iv] “Oregon Museum of Science and Industry (OMSI) Parking Lot Swales.” PortlandOregon.gov. 6 Jan. 2005. Web. 17 May 2014.
[v] Frank, Lawrence D., Peter O. Engelke, and Thomas L. Schmid. Health and Community Design: The Impact of the Built Environment on Physical Activity. Washington, DC: Island, 2003. 156. Print.