[With Video] Low Impact Development and Green Infrastructure on three types of roadways
September 03, 2020
September 03, 2020
Rural, suburban, and urban: Different transportation projects require unique solutions to deal with stormwater runoff and reduce damage to waterways
In my last blog, I talked about the best Low Impact Development (LID) and Green Infrastructure (GI) techniques for roads. These LID and GI techniques mitigate damage to our waterways from increased development. Road runoff contains sediment and other pollutants. If you are designing or retrofitting a road, you can use these techniques to slow down, soak up, and clean stormwater runoff.
But how, exactly, can you apply these techniques? How can they fit into the streetscape? In this blog, let’s look at how we can use these practices in different transportation contexts—on rural, suburban, and urban roadways. The techniques you use depend on what situation you’re working in. Let’s also dive into some real-world examples by considering several retrofit and new design projects on roadways in the province of Ontario, Canada.
In rural areas, there is usually more room on either side of the road for GI facilities. Rural roads don’t usually have a curb and gutter, and rural municipalities typically use some form of swale—a simple grass channel (ditch)—to convey and control stormwater.
Here’s an example of a rural roadway in Oakville, Ontario. William Halton Parkway is being extended, and an interim two-lane design is currently under construction. The interim two-lane strategy requires LID within the right-of-way area to provide water quality and protection against 100-year storms (which produce an onslaught of rainfall). Wetland/enhanced swales are a natural fit for the project, due to the number of watercourses along the proposed expansion and the amount of space beside the road. Enhanced grass swales have additional structures like check dams and longer vegetation to slow down water and allow for sedimentation, filtration, evapotranspiration (where water is transferred from land to the atmosphere), and infiltration.
Since this section of road will eventually expand to four lanes, there is two lanes’ worth of space for GI facilities. The wetland swale design has wide, low slope bottoms to encourage water quality treatment, infiltration, and flow control structures for detention. Interestingly, the swale acts like a wetland in terms of treating, conveying, and slowing down water. The weir structures—which are built of wood and change the flow characteristics of water—control both for slope and volume. The wetland swales send water to watercourses via vegetated swale.
In suburban areas, there is usually some room on either side of the road in the boulevard for GI facilities. These boulevards are getting smaller and smaller as our suburban neighborhoods get denser with more infrastructure within them, but there are still very good opportunities for GI in these areas. Suburban roadways typically have a curb and gutter and can range from small neighborhood roads to suburban collector—or arterial—roads.
Here’s a good example of GI and LID in a suburban roadway context, where we’ve been able to take advantage of larger boulevard areas in London, Ontario. The City of London implemented a retrofit bioretention (rain garden) pilot project on Waterloo Street as part of a planned utility upgrade. Bioretention is a process that removes sediment and pollutants from stormwater by filtering the stormwater using soils and plants. Due to the large mature trees and utility boxes along the street, we brought in regular gardens where rain gardens were not feasible to give the street a cohesive look. The City contacted the local neighborhood association to carry out the routine maintenance on the GI facilities.
These techniques will mitigate damage to our waterways caused by pipes carrying pollutant-laden stormwater directly to our lakes and rivers.
In areas where there is less boulevard space due to road widening or utility conflicts, LID can be used within the road right-of-way. Dixie Road, located in Peel Region, Ontario, is a major arterial roadway that has been widened from four to six lanes.
As part of the widening work on Dixie, we’ve installed LID measures in the form of a sewerless storm system. This system consists of a rock trench to infiltrate up to a 10-year storm event, with a StormTech chamber—an arched chamber that stores water and enhances GI techniques—on top to convey a 100-year storm. To control grades and direct surface runoff drainage of stormwater, we installed the system with less than a 1% slope and drops at each manhole. We added a catchbasin insert in every catchbasin to provide pre-treatment for the system and ensure the rock trench would not get blocked up by sediment.
We used another type of underground system (the kind that can work well in suburban situations because of the lack of surface boulevard) on Dundas Street in Burlington and Oakville, Ontario. We added underground infiltration chambers to treat and infiltrate the stormwater prior to discharge in multiple sensitive creeks with several animals and plants considered ‘species at risk.’ The LID system provided an estimated savings of $1.2 million over more traditional stormwater methods like offline detention ponds.
In an urban landscape, boulevards are often a lot smaller. These roads also have many demands on them, with street parking, pedestrians, bicycles, storefronts, and transit stops all potentially incorporated into that public realm space. At times, trying to fit LID in at the surface can be difficult. If it’s possible to incorporate LID, it’ll often be used to achieve more than one purpose.
For example, while working with the City of Newmarket, Ontario, we used LID on Yonge St. during a streetscaping and redevelopment project for the city. Along the street, we’ve implemented planters and soil cells to help city trees grow in a healthy way that doesn’t compress the roots. These street trees provide nice aesthetics, shade for pedestrians, and some protection for cyclists on a separated bike lane. But at the same time, these trees and planters can also filter stormwater as well as provide water quality treatment and filtration.
Redevelopment projects provide an opportunity to use surface LID or GI features—even if it’s in a compact manner. For example, for our work on the Vaughan Metropolitan Center in Vaughan, Ontario, we’ve used rain gardens to treat water from the street. These bioretention planters look like concrete street planters and they provide infiltration and filtration.
On urban projects, these bioretention planters can fit into streetscapes. They’ll often be concrete-driven—as opposed to the gentle slopes seen in rural or suburban contexts—and small. But they still get the job done.
As we’ve seen above, with careful design, LID and GI can be used on roadways of any size. These techniques will mitigate damage to our waterways caused by pipes carrying pollutant-laden stormwater directly to our lakes and rivers. It’s fascinating to see which strategies work best for different situations, and I’ve enjoyed learning about these distinctions throughout my career.