Eco-roofs and rain gardens can help mitigate runoff

Cities and municipalities are increasingly taking greener steps to treating stormwater with contaminants onsite before it heads back into our water supply. For multifamily developers there are plenty of opportunities to implement some of these practices with green roofs, parking lots or structures built with permeable pavement, landscaping and even the sidewalks around the building.

While there are many different ways for developers to handle stormwater, dealing with it is mandatory in some cities, with rules and regulations varying from state to state and even city to city.

“Cities used to think of rainwater as a curse,” said Linda Dobson, program manager for the city of Portland, OR’s Sustainable Stormwater Management. “But now we have moved beyond the narrow application of stormwater mitigation—it’s really a whole new approach to how we’re designing our urban environments now with a green infrastructure approach. Green infrastructure is a term we use a lot, and it applies to trees, eco-roofs, green streets and the like. It’s our way of focusing on watershed health.”

Not only do all of these green infrastructure elements help filter contaminants from rainwater, they also help cut down on flooding and can even help cut down on water costs by gathering rainwater and pumping it back into the building for reuse, such as water for flushing toilets.

Capturing H20

One way of dealing with stormwater is to simply build an underground infrastructure to collect rainwater and send it off to a treatment plant. But as Dodson points out, some of that rainwater is clean, so it doesn’t need to be treated, and if builders can treat the water onsite, many cities will give tax credits or breaks on water bills. For example, the city of Portland will give developers and/or builders 30 percent off of their water bill (the amount of the bill that focuses on treating stormwater) if they contain and treat the stormwater onsite.

Old solutions to new problems seem to be the best answer. Before cities turned into concrete jungles, there were actual jungles or forests there that would soak up the stormwater as it fell from the sky. But today the water pools and collects on the cement and causes all sorts of problems that need to be dealt with. Developers have numerous ways to treat this water, such as rain gardens, holding ponds, permeable pavers and green roofs.

“Capturing water at the source, before it even hits the ground” is one of the best options for dealing with stormwater, according to Dobson. Managing wastewater closer to the source saves on moving the water to a different facility to be cleaned. “Wastewater isn’t really waste; it can be a great thing.”

Dennis Wilde of Gerding Edlen estimates that the use of green roofs and bioswales can delay the runoff time by up to any hour and transfer up to 25 percent of rainwater back into the atmosphere. This greatly cuts down on the risk of flooding and preserves streets and sidewalks.

By installing a green or eco-roof on the top floor of a building, developers can capture and treat a great deal of stormwater onsite as the soil and plants pull out harmful contaminants. Treating the stormwater onsite, as mentioned earlier, will not only save money in utility bills, but Wilde claims a green roof can double the life expectancy of the roof.

ground solutions

Rain gardens are another option, and they can be installed on the street level, in patio space, or along parking lots or structures. Rain gardens operate in the same basic way as eco-roofs. In addition to collecting the rain that falls directly into the gardens, by leaving spaces, or cutaways, in the concrete surrounding the rain gardens, water from the that area can then flow into the gardens as well. Parking lots and streets make up the majority of impervious sections in cities, with each offering staging areas to collect and treat rainwater.

Disconnecting downspouts and sending water directly into planters is an easy way to treat stormwater. In a student housing facility near Portland State University, the downspouts flow into four connected rain gardens spaced out down a slight incline. Each garden filters more stormwater, and then at the last garden an underground cistern collects and then pumps the water back into the building to flush toilets. The gardens are responsible for treating 8,000 square feet of street-level water.

Dobson estimates that by turning a cement curb extension into a rain garden or bioswale, one could very successfully manage all of the stormwater for a 200-foot block.

Healthy infrastructure

“Another thing people don’t focus on very much anymore is, as cities urbanize, the food, cover and shelter for different species decreases. Eco-roofs are a great way to reintroduce structure back to the city and bring back pollinators, birds, and reintroduce the natural environment with the urban environment,” Dobson said.

Not only do rain gardens and eco-roofs help reintroduce wildlife into the city, they also create an atmosphere—one that green-minded clients are willing to pay for.

“From a developer’s standpoint, it makes bottom-line dollars and sense. They won’t have the added expense of an underground infrastructure to deal with the water, which is extra money when building, and at the same time you’re creating a much more attractive community and you get higher prices or rent for the spaces. They (the builders) are going to have manage their stormwater no matter what, so they might as well manage it to create an aesthetic appeal at the same time. “

Wilde agrees: “It just makes sense. We think it’s critical to creating a building environment that’s compatible with its neighbors.”

Gerding Edlen has done 12 green roofs in the Portland area and built the majority of its landscaping to help deal with stormwater.

Aesthetics and function

“It’s great to walk through the city and see all the nice landscaping,” Dobson said. “You can get really artful with the water features. And if they’re really successful, you’ll see these landscapes throughout the city and you don’t know that they’re also a functioning stormwater facility. They most likely would’ve done the landscaping anyway, but now they’re contributing to the green infrastructure.”

The landscaping and onsite water treatment also helps make the neighborhoods more pedestrian-friendly by not only cutting down on the amount of water on the sidewalks, but also giving the area curb appeal.

Let’s face it: When it rains, it pours, and when tenants are routinely looking for the greenest options on the market, eco-roofs, bioswales and rain gardens can be a smart decision both environmentally and financially for multifamily developers.