"It is used as a more earth-friendly means of providing drainage as opposed to concrete linings," said Carol Presley, an environmental engineer for Santa Clara Valley Water District.

Vegetated swales are used all over the state and nation, but most people don't even know they exist.

In rural areas the swales are used near farms and roads, and in urban areas they are commonly found near driveways, parking areas and other commercial and residential developments with impermeable surfaces such as concrete and asphalt. The vegetated swales are required by regional water-quality control boards and some cities.

They were not required by the city of Sunnyvale until recently. Sunnyvale now requires new developments and redevelopments to use swales or other flood management practices.

Typically, swales are not identified by signs, such as the one in the Cupertino library's parking lot, but Jason Chou, Cupertino public works associate engineer, guesses that a sign is there because someone questioned the use or the aesthetics of the land.

Without vegetated swales--sometimes called vegetated buffers--there would be more flooding, and water quality would decline.

Swales are typically covered with turf or other grasses and often include shrubs or trees. The vegetation is multi-purpose. It provides watershed management and pollution control, and it is supposed to be aesthetically pleasing.

"Bare dirt is lifeless. Vegetation opens up the soil," Presley says.

Population growth and suburban sprawl have covered significant portions of land with buildings, sidewalks, concrete gutters, driveways, roads and parking areas.

Where land once was available to absorb winter downpours and allow water to naturally percolate down, vegetated swales and other landscape flood and erosion controls now serve to slow water from running off hard surfaces and into creeks.

Creeks and storm drains are incapable of handling episodic events such as those that can come with the region's rains and will flood if not managed carefully.

"Creeks are being asked to take on a much larger volume than [they] normally would," Presley says.

Cobblestones placed at the end of a downspout, such as found at the Sunnyvale Senior Center, slow rainwater falling from the roof, in much the same way as swales slow water flow from parking lots.

In addition to flood and erosion control, swales also protect the water that ultimately flows into San Francisco Bay.

Motor oils, greases, antifreeze, hydraulic fluid and other lubricants drip or leak from vehicles to the pavement. Rain washes these off the pavement and into the swale or storm drain, but drains lead directly to the bay.

Fifty percent of the deposits of heavy metals such as cadmium and copper are directly linked to cars. They are bioaccumulative in invertebrates such as worms, clams and crawdads that live in the bay muds and creek bottoms, Presley says.

Birds and fish eat the invertebrates and thereby move the metals up the food chain.

The metals are natural components of the earth and in small quantities benefit the human metabolism, but higher concentrations can be poisonous.

Plants and microbes in the swales absorb and break down potentially toxic substances.

Fertilizers run off of lawns and gardens and cause algae bloom in creeks. The overabundance of algae sucks up the oxygen that fish need to survive.

Plants living in swales act as filters for nutrients, fertilizers and other chemicals that might otherwise go directly to water sources. Vegetated swales are more easily maintained and controlled in growth than miles of creeks, creek beds and other bodies of water where algae bloom occurs.

Presley says native perennial grasses such as purple needle grass are excellent choices for swales. The roots of the purple needle grass can grow more than 7 feet long. Roots absorb and hold on to water, sustaining the plant during drier months.

Native plants are more drought-tolerant, which means they require less water, aid in erosion prevention and are not likely to be invasive and spread uncontrollably, choking out all other growth.

Chou says anyone filing a building permit in Cupertino receives a list of best management practices that includes the recommendation, and requirement in some cases, of vegetated swales that may look like just a strip of land--but do a whole lot more.

El Camino Hospital