Slowing the Flow of Pollution Runoff to the Bay

Jan 1, 2009
Sejal Choksi
by Sejal Choksi

While the rainy season in the Bay Area can mean an end to nice weather and much-loved outdoor activities, it’s an important and productive time for our environment – rain prompts new plant growth after many dry months and replenishes water reserves for drinking and irrigation. In urban areas like ours, however, rain also becomes polluted runoff as it hits our streets and driveways, washing grease, oil, trash and fertilizer residue into San Francisco Bay. All our roads, buildings and parking lots are covered with concrete and asphalt, impervious surfaces that do not allow water to filter slowly into watersheds but instead send rainwater rushing to creeks and the Bay along with all the pollutants and trash it picks up along the way. Storm water runoff is the greatest source of water pollution for the Bay and for many of the important waterways in California and throughout the nation.

San Francisco Baykeeper has recently joined forces with Bay Area governments and agencies to promote an innovative approach to storm water management called Low Impact Development, or LID. The term refers to techniques that attempt to replicate nature’s way of dealing with runoff, which is to allow rainwater to pool or penetrate the ground’s surface slowly and be filtered through the soil before reaching creeks and the Bay. By using design elements that capture and manage runoff close to its source, low impact development can prevent storm water runoff into creeks, rivers and the Bay. These practices increase groundwater recharge, prevent soil erosion and reduce the amount of pollutants delivered to waterways by rainwater.

You may be familiar with low impact development techniques such as replacing paved surfaces with native grasses or gardens – including installing a green roof, a practice which is gaining fame in the Bay Area after a large-scale garden was planted atop the new California Academy of Sciences building. The Academy’s garden uses native plant species to cover the 197,000-square-foot roof and will provide a habitat for Golden Gate Park’s surrounding wildlife, as well as  annually absorbing an estimated 3.6 million gallons of rainwater that might otherwise turn into polluted runoff. But you don’t need to build a multi-million dollar structure to incorporate LID practices into your home or business. And, LID techniques aren’t just meant for new buildings and development: they can be incorporated into existing structures with only a few adjustments.

One simple LID technique that can be used on nearly any building is collecting rainwater for household use. By redirecting your home or building’s gutters to deliver storm water to a rain barrel or cistern, rainwater can be stored for landscape irrigation during the dry season or used for indoor plants during the rainy season. Best of all, the technology is readily available and relatively affordable. The City of San Francisco recently launched its Rainwater Harvest Campaign that includes a partnership program with a local hardware store to subsidize the purchase of rain barrels for local residents. The City expects that the program will allow for 325 sixty-gallon rain barrels to be purchased by residents. Each of these barrels will amount to thousands of gallons of captured and reused rainwater, preventing polluted runoff and conserving tap water.

Another do-it-yourself LID project is building a rain garden, which aims to slow down rainwater with shallow plains, plants, rocks or temporary ponds. Rain gardens give water a chance to percolate through the ground instead of being channeled straight to the nearest creek or Bay. This percolation process naturally filters pollutants out of the water and nourishes plant life. An added benefit is that rain gardens double as mini wetland sanctuaries for both animals and humans – a nice reprieve from concrete and pavement in our urban surroundings.

When homes and buildings around the Bay Area are fitted to capture and absorb storm water, the amount of polluted runoff to the Bay is significantly reduced, which means a healthier marine environment for the birds, seals, sea lions and fish that live in the Bay. Additionally, these LID practices can collect a significant amount of water that will help ease the growing demands on California’s water supply.

Storm water runoff is a low-profile but high-impact source of pollution to our waterways. San Francisco Baykeeper is the Bay’s pollution watchdog, working to reduce the negative effects of storm water runoff as an essential step toward keeping Bay waters clean. For more information visit

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