As water runs down roofs, over driveways and patios and off other impervious surfaces, it might pick up pollutants as it flows directly into streams, wetlands, lakes and groundwater aquifers.
Stormwater runoff from impervious surfaces has been routed directly to streams through stormwater pipes and ditches with little infiltration or treatment, according to Derek Godwin, Oregon State University Extension Service water management and conservation specialist. That's because municipalities focused on getting the water off the property as quickly and efficiently as possible.
However, stormwater runoff has become the No. 1 source of residential pollution for waterways. It also increases potential flooding. Municipalities have responded, installing rain gardens, a type of green infrastructure, in public and commercial spaces to slow down and treat the water before it enters streams, wetlands, lakes and groundwater aquifers. They encourage homeowners to build them, too.
Designed and installed properly and planted with the correct plants, rain gardens are like tiny water treatment facilities. Water gathers in the rain garden, soaks into the soil and is taken up by plants. The water not used by plants moves into deeper soils and groundwater or flows more slowly to nearby streams. The plants and soils filter nutrients, sediments and toxic materials from the runoff before it gets to waterways.
"Homeowners interested in treating stormwater runoff with rain gardens should first familiarize themselves with how runoff from their roof, driveway, sidewalk and roads are currently being routed and treated," Godwin said. "Runoff water moving on the surface could be incorporated into a rain garden design with sufficient area and infiltration rates. Runoff drains into the rain garden downslope from foundations and, if it can't all be absorbed, flows out to a safe, designated location at a slower rate than from impervious surfaces."
Runoff water being piped underground to a street curb and stormwater drain would need to be modified by disconnecting the downspout and routing the water to a rain garden. Godwin recommends checking with your local jurisdiction to see if building and routing runoff through a rain garden would benefit water quality, reduce flooding and be permitted for individual property conditions. If approved, the municipality will provide any requirements you must follow such as where to safely route water during large storms to prevent erosion and protect nearby homes, roads and other infrastructure.
