Bioswale design is being implemented more and more in the Bay Area. Its design function is to help reduce pollutants that otherwise would flow freely to waterways and eventually to the Bay and the ocean.

Rain water that runs of solid surfaces like roadways parking lots and sidewalks collects dirt and other contaminants such as metals and oils. The turbulence caused by fast moving water will keep these pollutants suspended in the water. If the water-flow is slowed down it gives time for the dirt and other pollutants to settle out of the water This is what bioswales are designed to do.