We are well into a rainy winter here in the Bay Area, and that means a lot of things — flash floods, erosion, and inconvenient bicycle commutes — but it also means pollution. The rain that falls on city streets, sidewalks and parking lots flows to storm drains and into the Bay, picking up pollutants like PCBs and mercury along the way. Additionally, many of our stormwater systems are aging and unable to deal with the heavy flows that come from larger storms. Over the last century we have paved over an ever greater portion of the Bay Area’s landscape. More and more water flows down the storm drain instead of being taken up by plants or filtering into the ground.
Cities around the region are beginning to adopt techniques that mimic the function of natural landscapes to help manage their stormwater loads. These systems are called “green infrastructure” because they use natural processes to move and manage stormwater, as opposed to conventional, gray infrastructure systems, where water is immediately diverted through pipes and drains.
Green infrastructure seeks to slow, capture, filter, or absorb water before it flows down a drain. Three of the most common techniques are:
- Rain gardens (bioinfiltration) are depressions filled with plants that can help take up water, reducing how much goes into the sewer system and the amount of pollution in the water. Rain gardens can be exceptionally beautiful, but require a relatively large and flat site.
- Permeable pavement is used to convert parking lots, walkways, and other light-use paved surfaces from impermeable surfaces to surfaces where water is able to filter through soil and gravel below.
- Bioswales are gently-sloped, vegetated landscapes that allow water to flow through them and filter out pollutants and silt before water enters storm drains.
Regional Stormwater Permit Mandates Green Infrastructure
Cities are growing increasingly interested in using this technology in part because the regional stormwater permit requires cities to use these techniques to reduce the amount of mercury and PCB that flows into the Bay from urban runoff. The regional permit encourages cities to reduce water repellant surfaces and maximize vegetated surfaces that will absorb stormwater, rather than letting it run to the Bay. The plants and soil will filter out toxic mercury and PCBs in what will ultimately be a more resilient and sustainable system.
Green Infrastructure in Action
Regulations aside, the flexibility of green infrastructure means that it can suit needs as diverse as those of our cities. In San Francisco where large storms overwhelm an antique sewer system and flooding is a concern, the San Francisco Public Utilities Commission has begun to install green infrastructure sites throughout the city as a part of their 20 year, 6 billion dollar Sewer System Improvement Program.
These sites are intended to slow the flow of water during major storm events. San Francisco’s sewer system treats both wastewater and stormwater together (systems that are separate in other Bay Area cities). When the combined system is overwhelmed, some of the water must be released without being fully treated.
Planners are also taking advantage of green infrastructure’s aesthetic appeal to reimagine streets as both less burdensome on water management infrastructure, but also more pedestrian and bicycle friendly, more livable, and more beautiful. At sites such as the Newcomb Avenue Green Street in the Bayview Neighborhood of San Francisco, green stormwater management is being installed in concert with streetscape improvements and traffic calming techniques. In addition to creating a more pleasant and resilient urban environment, peak flows of rainwater to the sewer at this site were reduced by more than 75%.
In San Jose where there is a housing shortage and lack of densely developed areas, the city’s plan is to develop urban villages in which public streetscape improvements accompany private mixed use development. San Jose plans to curb the amount of mercury and PCBs it releases into the bay by treating more of its stormwater through green infrastructure projects at these kinds of sites.
In the East Bay, the cities of Oakland, Emeryville, Berkeley, Albany, El Cerrito, Richmond, and San Pablo are working with the San Francisco Estuary Partnership and Caltrans on a project called the San Pablo Green Stormwater Spine. They plan to install rain gardens, stormwater planters, and other low impact development projects to filter polluted runoff and to calm traffic and provide greenery along San Pablo Avenue. These projects have not broken ground yet, but once complete they will treat runoff from more than 4 acres of impervious surface and help beautify and calm traffic along a major thoroughfare.
What Can We Expect to See?
As stronger storms, rising sea levels, and increasing development put more and more strain on our aging systems, the challenges of stormwater management will grow. Green infrastructure can help solve these problems by slowing down and cleaning water before it flows into storm drains and out into the Bay. Furthermore, green infrastructure mimics the processes of nature and benefits communities by minimizing the urban heat-island effect, calming traffic and beautifying our streets.
We need our cities to move forward with these kinds of projects now; our limitations of our gray infrastructure are real and green infrastructure technology is proven and available.
As the Bay Area experiences rapid urban growth and population expansion, investments in green infrastructure will be vital to minimize the negative impacts that development has on the quality of the Bay. Stay tuned to learn more about green stormwater management and how we can help the Bay Area better minimize polluted runoff.