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This story was originally published by Mother Jones and appears here as part of the Climate Desk collaboration.
In 2021, on San Francisco’s wettest October day on record, an “atmospheric river” dumped a stunning 4.02 inches of rain downtown, causing highways and neighbourhoods in the area to flood. Cars were stranded in standing water. And the city’s sewers, which carry both stormwater and sewage, overflowed in the low-lying Marina neighbourhood. Officials estimated that 1.4 million gallons of untreated water could have escaped into the bay. For the approximately 700 municipalities in the United States with combined sewers, overflow can happen during periods of heavy rainfall and can lead to polluted waterways, closed beaches, and tainted drinking water. And with climate change, heavier storms are on the horizon. So about 10 years ago, San Francisco began to turn, in part, to a simple solution: planting dozens of public rain gardens.
At the most basic level, rain gardens function like sponges. They are typically made by digging five or so feet into the ground, adding layers of rock and soil mixes designed to absorb and filter water, and topping the layers with flowers, trees, and shrubs. A finished rain garden should dip like a bowl about half a foot below ground level so that when it rains, the garden can temporarily fill up, allowing water to percolate into the ground rather than run into the street.
And, research shows, the gardens are remarkably effective at capturing runoff. When San Francisco’s Public Utilities Commission, for instance, installed 30 new rain gardens along a 12-block strip in the city’s Outer Sunset neighbourhood, the corridor reduced the amount of stormwater entering the sewer by 95 per cent for the area, taking in about six million gallons — more than the volume of the iconic Lincoln Memorial reflecting pool in Washington, D.C. — per year. On a smaller scale, individual homeowners who install rain gardens to collect runoff from roofs and gutters can expect to soak up an estimated 30 per cent more water than they would with grass lawns.
Plus, rain gardens, which often include low-maintenance native plants, offer a wealth of other benefits. “Some people think of rain gardens as just kind of glorified ditches,” said Jennifer Cooper, who manages the Landscape Architecture Bureau for San Francisco Public Works. “But they can be more.” They’re commonly used to filter runoff pollution, and they can also reduce urban heat, offer habitats for pollinators, and serve as scenic gathering spaces for people.
Cooper and her colleagues designed one of the Outer Sunset rain gardens to double as an outdoor classroom. Situated across from St. Ignatius College Preparatory high school, the 1,200-square-foot garden is shaped like a kidney bean and is full of Cleveland sage, yarrow, coyote brush, sticky monkey-flower, toyon, and rosemary. It includes four rows of benches, a handful of boulders, and as Cooper pointed out to me when I visited in October, stepping stones made from recycled granite street curbs. (Wildlife seems to like the place, too — my rain garden tour was punctuated by a visit from a blue heron.)
San Francisco is far from the first place to collect its rain. Portland and Seattle were among the first cities in the United States to adopt rain gardens and other water-absorbing features like green roofs and permeable pavement, which allows water to seep through it rather than pooling on top. Today, cities around the world, including Denmark, Poland, Singapore, and Brazil, among others, are incorporating rain gardens into their urban landscapes.
But convincing city officials to choose green infrastructure over more traditional, “gray” technology, like concrete pipes, hasn’t come without challenges. Rain gardens require green space, which may be limited in dense urban areas, and workers often need special training to maintain them. Plus, they can look a bit unconventional: Native shrubs planted in a hollow ditch aren’t exactly the pristine, manicured look desired by some people.
Many of the experts I spoke with said a major hurdle is the task of convincing planners to embrace a new way of thinking. Even with “very strong” data supporting rain gardens’ benefits, the default among regulators, designers, and engineers is often traditional drainage pipes, according to Brendan Shane, the climate director for the Trust for Public Land, a national non-profit aimed at expanding access to nature.
As climate change brings increasingly heavy rain, cities would be wise to suck it up. Consider: Two months before San Francisco’s heavy rain event in October 2021, New York City issued its first-ever flash flood emergency warning. The storm killed at least 13 people in the city, mostly in flooded basements, in part because, given that nearly three-quarters of the city’s surfaces are made of impervious material like concrete, the water had few places to go. In July 2022, St. Louis saw record-breaking rains, and days later, floods in Kentucky killed dozens of residents.
Major flooding events also occurred last summer in Las Vegas, Arizona, and Texas. In fact, heavy rain events have increased in much of the country since 1958, according to a 2018 federal climate report, with the biggest increases in the Northeast, by 55 per cent, and the Midwest, by 42 per cent. Often, it’s low-income communities of colour, where decades of underinvestment means greenery is scant, that suffer disproportionately from these events. According to a 2021 analysis of 38 major U.S. cities, for instance, formerly red-lined neighbourhoods have 25 per cent more homes at risk of flooding than non-red-lined, mostly white neighbourhoods.
Rain gardens, of course, are only part of the solution; a 10-foot-wide depression in the ground won’t solve, say, the drivers of climate change or environmental racism, and it can’t on its own protect us from megastorms. The good news is that, for cities able to dig for it, money for green public works is available. In addition to the billions of dollars in existing funding options with the Environmental Protection Agency, Congress’ Bipartisan Infrastructure Law includes more than $50 billion for water-related projects, while the 2022 Inflation Reduction Act includes $2.8 billion in funding to help underserved communities become more climate resilient. While grants are up to individual agencies to award, said Lydia Olander, director of nature-based resilience at the White House Council on Environmental Quality, “there are a number of places” where rain gardens could fit under both new laws.
Individual homeowners can make a difference, too. For those who want to add a rain garden to their yard, the EPA recommends looking for reimbursement programs through local and state public works offices. With city funding, for instance, the Trust for Public Land’s Shane paid “almost nothing” to put a rain garden capable of holding several hundred gallons of water in his own backyard in 2022. It’s one of at least 4,000 properties D.C. has souped up with rain gardens, rain barrels, permeable pavement, or other green projects in the past decade or so. “Each one is small, but when you add them up,” he said, “you start to see really big impacts on the volume of runoff, on the quality of water.”
Learn how to install and fund a rain garden on this rain garden resources page.
Comments
I have some issues with blanket environmental policies like rain gardens. They are not applicable to every urban ecosystem. They are also too often portrayed with a certain naive unicorn-like awe, but not apparently in this article which otherwise tends to portray anecdotal success in one location as universal.
Here's the situation in Vancouver, the rainiest large city in the nation. The entire Metro is underlain with rock hard glacial till. Within my 33 years in urban design, not one rain garden or rock pit worked. The reason they did not work is that percolation into the ground water is all but impossible with a 25 metre thick layer of glacial till just centimetres below the surface. Further, if you try to drill through the till you'll puncture the cap on a humongous subsurface pressurized aquifer. The water will never stop flowing -- just ask any local geotechnical engineer.
Moreover, the term "rain garden" produces glassy eyed dreams of a sustainable city in the heads of too many landscape architects, architects and planners without regard to their practicality. The low lying city of Richmond BC had open ditches lining every road and mown front lawn for 100 years, then they started diverting them into storm sewers because they were perceived as ugly. They were, in fact, dangerous to kids and car drivers. Today, they'd be called "rain gardens" and planted up with aquatic plants that in real practice will never be maintained and be soon taken over by garbage and invasive plant species.
The Godzilla of invasives is Japanese knotweed, a plant that loves ditches and spreads vegetatively on the surface (even a tiny fragment stuck to the sole of a shoe can grow a new plant elsewhere) and can send foundation-busting shoots 10 m underground in a single year. There are no native biological controls for knotweed. The only known effective control of this plant is to fence off an infested area and to make judicious multi-year applications of 24-D laden Roundup on the leaves.
Yes, the entire subject is complicated.
Still, the design consultants and planners with no field experience love their skinny, pretty ditches - er - rain gardens and bioswales. Maintenance is a dirty word to them, mainly because they download the maintenance ramifications of their plans to strata boards and commercial developments who hire landscape contractors to maintain the landscape with chemicals and noisy machinery.
So what does work? This is where joined up thinking at a larger, city-wide scale is needed. First, sustainability is so much more than glorified ditches. If open lawns with ditches are seen as a positive thing for stormwater management and environmentalism, then environmentalists would love suburban sprawl. Say what? Let's start with the fact that our cities must become more compact, walkable, energy efficient, poly-zoned and transit-rich. While this will rightfully constrain the available open space for wasteful rain gardens, the urban tree canopy can become even more effective when trees planted in narrow paved pedestrian streets have extensive subsurface vaulting for their root systems. The vaulting structures will result in healthier trees and less area of paving damaged by roots, which are otherwise directed downward into the vaults filled with a nutrient-rich growing medium and an automated drip irrigation system. Essentially, an entire street can be underlain with a gigantic conjoined tree root vault system, which will result in a solid healthy canopy of green leaves overhead. Google "Deep Root Vaulting System" for actual projects.
So how do you manage the storm water in compact towns in a temperate rainforest? First, rain gardens and bioswales must never, ever be seen as replacements for a decent storm sewer system. Many developers love them because sewers are expensive to build, and that cost is inevitably passed on to their home buyers. Then again, cities cannot afford to replace them in future without increasing local taxes, which is one of the most notable and highly unsustainable hidden subsidies for sprawling, unsustainable car dependent suburbia.
Storm water management today means underground storm sewer infrastructure is directed into artificial wetlands at the bottom of the entire system. In that light, existing natural wetlands near urbanized areas need to be preserved and new artificial wetlands constructed nearby to accept, filter and clean urban runoff before it enters salmonid habitat or the sea. Instead of building last century's subdivisions, urban designers and senior politicos need to first infill large lots and mall parking lots with Missing Middle forms of housing and commercial development in existing cities and suburbs. The subdivision planning model for greenfield sites must, in my view, be banned in favour of genuine town planning principles where compact towns and villages with all the necessary amenities of life are contained within their boundaries, and where stormwater is directed into modern sewers with large downstream wetlands.
In addition, there is so much rain on the West Coast that it's a mystery why it isn't harvested in larger quantities for non-potable uses, like garden and park irrigation, fire suppression and so forth. Some individual projects and buildings harvest and store rain water to flush toilets and water planting beds, and these are usually included in LEEDs calculations to win awards for sustainability. Why can't a city look at harvesting tens of millions of litres of rain water and storing it in water towers or large underground cisterns buried in parks to use in the fire hydrant network, mass plantings in public parks and street tree irrigation systems?
Toronto has combined sewage and runoff systems. The streets around me have been dug up for about a decade, as telephone, hydro, water and sewers are rebuilt. For some reason, they can't work in one spot and do the whole thing, street by street. Instead, each has to involve digging up the street, sidewalk and front yards of people along the street, doing the work, building a new concrete road, grinding its surface to accept asphalt, and finally asphalting ... with workmen using ill-maintained johnny-on-the-spots stinking up to high heaven the area they work in. And taxpayers pay for that to be done 5 or 6 times in a decade, instead of just once.
Of course, nothing makes as much sense as digging up this summer the asphalt freshly laid last summer. Who could begrudge so much unnecessary work for (private) international construction cos.