Put a LID on Stormwater

A stroll down a stretch of 2nd Avenue Northwest in Seattle is practically a walk in the park. The slightly meandering residential street is lined with wide strips of native grasses, small shrubs, and trees. Along the shoulder, interspersed among parking spots, are ponds and swales—gentle depressions—that fill with water during a downpour. What you won’t find are sludgy gutters brimming with muddy water and trash, or deserts of black asphalt stretching from property lines to the roadway.

The street was the city’s first experiment in what it calls “natural drainage systems.” A decade ago, the block was jackhammered up and rebuilt to catch and clean stormwater the way it’s done in a forest: by helping rainstorms soak into the ground, get sucked up by plants, or captured in their branches and leaves where the water evaporates slowly. The project—called SEA Street—has been wildly successful, nearly eliminating stormwater runoff even during heavy rains. That’s right, runoff on this street was reduced 98 percent during winter rains.

Natural drainage systems are cropping up slowly on streets across Seattle. And other Northwest cities are doing similar projects to curb runoff without pipes and holding tanks. The city of Portland even has an “ecoroof” blog site geared toward innovative stormwater solutions. Vancouver, BC, is building rain gardens at bus stops, among other projects. It’s all part of a movement called “low-impact development” or LID.

For years we’ve known that traditional infrastructure for funneling stormwater away from buildings and roads and into lakes and bays by using pipes and ditches doesn’t work. It fails for people: the systems are regularly overwhelmed, leading to flooded basements and raw sewage pouring into public waterways. It fails for nature: salmon and other species are poisoned by the polluted stormwater and quiet streams are transformed into torrents of filth.

The logic of LID is to try to replicate what Mother Nature does naturally by using engineering tricks and limiting sprawl.

Washington is at a crossroads for low-impact development. The state Department of Ecology, working with a technical advisory committee, is crafting a set of requirements specifying where and how to use LID. The stakes are high. If Ecology comes up with stringent standards that require widespread use of legitimate LID strategies, Puget Sound could reap great benefits. If it doesn’t, the fight to save the Sound could be lost due to the steady drumbeat of destruction from stormwater.

“Time is not on our side,” said Tom Holz, a stormwater/LID expert who’s on the advisory committee. “We may lose the battle just simply through dallying.”

Dealing effectively with stormwater requires a two pronged approach:

1. Stop sprawl—In an undeveloped setting, stormwater is essentially non existent. The best way to reduce runoff is to minimize the footprint of development.
2. Use low-impact development—When development does happen, it must be LID. Already built neighborhoods should be retrofitted over time using LID techniques.

Both strategies are important. Limiting development is critical because you can’t cut down very many trees or lay much pavement before getting damage from stormwater. In fact, top stormwater scientists say that when as little as 10 percent of a watershed is covered by impervious surfaces, streams and wildlife begin to suffer.

That realization led local stormwater experts to develop what is called the “65-10-0” rule or just the “65-0” rule for development. It’s shorthand for the need to leave 65 percent of the landscape in vegetation, while allowing a maximum of 10 percent “effective” impervious surface, which should result in zero runoff. (See this explanation of the science in a paper by University of Washington professor Derek Booth).

Right now the 65-10-0 rule is just a recommendation, not a requirement, in Ecology’s “Stormwater Management Manual for Western Washington,” the document that serves as the stormwater-regulation bible for the state’s largest cities and counties. But that could change with the work being done to update Ecology’s LID rules, an update that’s required because of a successful legal challenge of the existing guidelines by a coalition of conservation groups. The new rules are expected next summer.

So how do we get to 10 percent effective impervious surface in new development, and what on earth does that actually mean?

It means taking surfaces that normally repel water—roofs and driveways—and making them spongy. For roofs, that can mean building green roofs that are covered in soil and plants that trap and hold water where it falls. Seattle’s City Hall, the new Bill & Melinda Gates Foundation building, and the Portland Building are all capped in green roofs. Other LID strategies include downspouts hooked to rain barrels to store the water that does run off, or perhaps the downspouts flow into a rain garden landscaped with ponds that are lined with specially engineered gravel and soil that soak up larger volumes of water. Driveways are built from a lattice of pavers that leave some of the soil exposed. There’s also permeable concrete that allows water to soak through it, which can be used for sidewalks and roadways.

To reach that 10 percent goal, buildings need to get smaller, perhaps going vertical to shrink their footprint but maintain space indoors. These strategies generally are applied to new development, but are also applicable to retrofits of built areas.

The use of LID could get a
boost when Washington’s lawmakers convene next month. They’ll be considering legislation that would create a fee for petroleum products. Forty percent of the fee would be would available to cities for LID retrofit projects that cleanup and stop oil pollution from stormwater.

What’s great about LID is that when you consider all of the benefits from these strategies, it’s actually cheaper than the traditional storm-drains-and-pipes infrastructure. So you get the benefit of helping salmon and preventing flooded basements, all while saving money! And there are now lots of examples of affordable, successful LID projects from around the Northwest—examples that we’ll share in more detail in a post next week.

This post is part of a series on stormwater. Please also see:

• “Smart, Cheap Stormwater Fixes“
• “Water Pollution Enemy is Us“
• “Jesus Walking Salmon and Stormwater“
• “Stormwater’s Costly, Stinky Wake-Up Call”
  

SEA Streets photo courtesy of Seattle Public Utilities. New development in Snoqualmie photo courtesy of Flickr user midd1999 and driveway pavers photo courtesy of Flickr user Jamiriquai under the Creative Commons license.