San Francisco Could Find Downstream Benefits in Innovative Street Paving

Source: Chicago's <A href="">Green Alleys Handbook</a>Source: Chicago’s Green Alleys Handbook

During the heavy rainfall season, San Francisco faces some daunting challenges: Draining the water, keeping the roads from getting slippery, and containing and treating the runoff. Some storms are so severe that the city can’t keep pace. That’s when we see flooding in the Muni tunnels and sewage discharges into the bay.

But the solution — or at least part of the solution — could be as simple as changing the material that we use to pave our streets.

The city considered a wide variety of low-impact-design techniques for managing water at community meetings held in 2007. Among the solutions was permeable pavement, a technique dating back centuries that fell out of favor during the fast-and-cheap highway booms of the last few decades.

As Miles Chaffee, President and founder of Milestone Imports explained to Streetsblog, the benefits of permeable paving are numerous. "It decreases impervious land coverage, provides a more stable load-bearing surface, and allows the water to go into the ground," he said. "It eliminates the need for detention ponds, which require additional space. And it takes off a lot of stress from the sewer systems when it’s done correctly."

In addition, permeable paving can be made lighter in color, which reduces the urban heat island effect. It can be made of recycled materials, such as concrete and rubber, and by filtering the water, it removes pollutants. There are advantages for bicyclists as well: "It takes that film of water off the ground that makes it slippery," Chaffee said.

Municipalities around the country are starting to notice the benefits of permeable pavement. In Maryland, Montgomery County’s "Rainscapes Reward" program offers homeowners a subsidy of up to $1,200 for converting a driveway from impermeable asphalt.

An alley in Chicago, before and afterAn alley in Chicago, before and after

San Francisco has already begun work on projects with permeable paving, including innovative green streets construction on Leland Ave. and Newcomb Ave. According to the SF Planning Department’s Andres Power, "Newcomb will be the first true green street in San Francisco. From a policy and design perspective, there has been a sea change; it is infinitely easier to be able to talk about this stuff. Good design feels much less like an impossibility."

The upcoming Cesar Chavez redesign will incorporate green street techniques as well, stretching from the 101 interchange "hairball" to Guerrero.

And San Francisco homeowners will be expected to pitch in: a new landscaping law requires that at least half of newly-constructed front lawns be water-permeable, whether through pavement, bioswales, or raingardens.

Cities like San Francisco, Chicago, and Portland can boast about early adoption of permeable pavement. The technique has long been favored in Europe (where some streets retain cobblestones dating back hundreds of years), but is still viewed with skepticism in the United States.

"They haven’t quite gotten to where they’re convinced that they can do streets that are low-maintenance," said Milestone’s Chaffee.

Milestone imports porphyry, highly-durable paving stones that, when bonded by Propoxy, form a permeable pavement. In addition to its water management benefits, porphyry boasts another ecological advantage: reusability.

"When they have to dig up an asphalt street, they typically can’t reuse that asphalt," Chaffee said. "Whereas with a permeable pavement, they dig up the cobbles … fix whatever it is underneath, put everything back in — including the exact same stones — and reuse everything." Despite being called "cobbles," modern porphyry pavement isn’t bumpy or roughly textured: it’s ADA-compliant for wheelchairs, which means it’s also easy on bikes.

Pavers like porphyry are just one of many solutions. A report by Curtis Hinman at Washington State University identified four successful surface types for constructing water-permeable pavement:

  • Permeable asphalt — Used for light traffic roads and parking
  • Permeable concrete — A well-regarded, generally-successful material
  • Permeable pavers — Best used for low-speed traffic
  • Flexible plastic grid systems — A grid filled with gravel or soil, sometimes planted with grass

Whichever method is used, it requires a thorough hydrological analysis prior to installation, since drainage and water flow can vary widely from one street to the next. It’s wise to augment pavement with other ecological best practices such as rain gardens, bioswales, and street trees, all of which absorb, retain, and help to clean storm water. Rain barrels and eco roofs also provide a significant boost to pavement-based water management techniques, which is why San Francisco’s Public Utilities Commission offers subsidies and instructions to residents interested in harvesting rainwater on their property.

Portland has also positioned itself at the forefront of innovative water management techniques. "We can talk about all the multiple benefits that greenstreet facilities provide, but the bottom line is it saves taxpayers’ dollars," said David Elkin, a landscape architect with the city’s Bureau of Environmental Services. "Instead of just a patch or trench in somebody’s street, we’re going to leave behind a green, vegetated facility."

Chicago is taking steps to improve its urban watershed as well, with its much-admired "Green Alley" program. Featuring 5,000 alleyways comprising around 1,900 miles of pavement, the city’s goal is to convert flood-prone asphalt into hydrologically sensitive conduits that include permeable surfaces, strategically-placed drainage pipes, and recycled pavement.

Vancouver's <a href="">Country Lane</a>Vancouver’s Country Lane

Another city on the forefront of modern water management is Vancouver, which was once home to a dense network of creeks and streams. One tiny side street, Country Lane, has become a success story often cited by studies seeking to replicate the project’s implementation of permeable pavers, plastic grids with grass, and subsurface drainage.

Of course, features such as these cost more than a simple asphalt surface. Porous concrete is estimated to cost between $2 and $6.50 per square foot, interlocking pavers from $5 to $10. But according to Chaffee, the cost of installation is dwarfed by the alternative: deteriorating storm drains and overburdened water treatment plants that require expensive maintenance. That’s consistent with findings in Chicago, where city officials observe that the high costs of improving alleyways is offset by decreased maintenance and operational costs.

Money is one obstacle to installing ecologically sound pavement. Time is another.  The San Francisco PUC’s water management charrettes were held three years ago, and feasibility studies continue to this day.

But perhaps the greatest obstacle is public awareness and confidence. Many people simple don’t know of permeable pavement or its benefits. Chaffee believes that word will spread once more high-visibility projects appear in cities around the country. "There’s going to be a tipping point," he told Streetsblog, "people are going to start seeing the benefits. It might start in neighborhoods first. And neighborhoods will push it forward through the city."

  • Michael Baehr

    The PUC famously did the math and calculated that it would cost less to ship everyone who wants to surf to Hawaii for a week than it would to cut the number of yearly combined-sewer overflow events from 8 to 7. As a surfer, I’m still waiting for my ticket.

    Ergo, adding any more capacity to the system at this point is prohibitively expensive. We can only really look at cutting down on water input. If we want to make any improvements, we need to look into things like porous pavement, downspout disconnection, rain catchment, etc.

    That, or we can settle for occasionally discharging nearly-untreated raw sewage into the ocean. Eww.

  • “a new landscaping law requires that at least half of newly-constructed front lawns be water-permeable” meaning you can’t pour conrete over the front yard for off-street parking? Sounds good to me.

  • I heard that the soil underneath had to be removed every 5-6 years b/c its so contaminated from dirty runnoff? Does anyone know if this is true?

  • Nick

    What effect would this have on cars leaking oil into the street? Wouldn’t it soak into the groundwater when it rains?

    After all, those expensive “street cleaning” machines that rumble by at 5AM aren’t designed to keep the street visibly clean. Their purpose is to attempt to clean car oil off the street so that it doesn’t flow into the storm drains once it rains.

  • Jym Dyer

    @Wai – It already is illegal to pave over the front yard to provide parking, but that law goes unenforced and is routinely violated. It is, however, legal to cover the front yard with pavement if a garage is installed. This should be amended to require permeable surfaces. It would also help prevent garage/basement floodings!

  • ZA

    @ Nick –

    *Within reason,* petroleum products do break down over time, and arguably present less of a risk to the Bay by slowly working through soil layers with hungry bacteria than dumping all of it into a stormwater channel that exceeds a wastewater treatment plant designed decades ago.

    I still think there shouldn’t be leaked oil to begin with – and as the first rains demonstrate every year, all of San Francisco’s drivers should be taking better care of their cars.

  • Michael Baehr

    Our wastewater plants aren’t obsolete, @ZA. The Oceanside plant, for one, is one of the more advanced in the country.

    It’s just too damn expensive to add any more capacity to the system. We’ve already made great strides as it is; there used to be 50-60 overflow events in a year.

  • ZA

    @Michael Baehr – I was writing in the generic. Also, the Bay isn’t fed by San Francisco alone. The sewage spills from Marin County and San Jose are partly due to old infrastructure.

    Permeable surfaces, as with any technology, have appropriate and inappropriate uses.

    For San Francisco, I think almost every ancient creek covered with asphalt road should have a permeable surface. The old ponds now covered with houses and basements kept dry only by (energy inefficient) sump pumps need to be thought over carefully.

  • Permeable pavements have a lot of advantages, but they also require good maintenance. If they aren’t cleaned, vacuumed, repaired, etc., on a regular basis, they will cease to infiltrate water and will function more like conventional pavement.

  • For another option to reduce run off to sewers, SFPUC is offering discounted cisterns and rainbarrels for sale through the Urban Farmer store. Rain water is great for watering the garden.

    I’m not sure why, but this program seems to be going completely under the radar.

  • Rasty

    Dripping used motor oil is a problem. Not just for the petroleum which might eventually get broken down by bacteria. But don’t forget it also contains metals and other toxics. (And we also see dripping coolant with rust particles…)
    But the cars that account for most of the problem are just the ones that won’t get fixed. If you own a car with a blue book value of $700, you won’t and probably can’t afford to spend $400 getting gaskets changed out.
    Nick has a point worth studying here. After all, old military bases where chemicals were purposely or carelessly dumped on the ground are still Superfund sites 60 years later.

  • Permeable pavers with a proper substrate will filter out anywhere from 65 – 80% of all harsh metal pollutants. A company by the name of Permpave ( I understand has been doing a great job in this area with their permeable paver lines. Anyone interested should look into them as i understand they just worked with the City of Chicago and Miami as well as Citifiled in NY and the results turned out pretty well

  • I’m curious to know more about what this does to the ground beneath the absorbing pavement. I really want to have a rain garden for my house, and then use red wiggler worms to make a rich compost for the garden. I can just imagine the plants that would come from that.

  • Fantastic, Your article is very informative. You have described the installation process perfectly with the help of picture-gallery. Good Luck with the upcoming updates.


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