Stormwater & Natural Drainage Systems (NDS)

What is stormwater and why is it a problem?​

Stormwater is water that falls during a rainstorm or melting snow. In developed areas such as Seattle, we have many hard surfaces such as roadways and rooftops that do not allow water to soak into the ground. Flooding occurs when a lot of water runs over hard surfaces.

The runoff from drizzling or pounding rain also picks up fertilizers, pesticides, soaps, and other pollutants from the ground. It transports them to the nearest storm drain and local waterways, contaminating water quality and harming fish and other wildlife.

The City of Seattle is working to reduce the amount of polluted stormwater runoff flowing into Thornton Creek and Lake Washington.

Natural Drainage Systems (NDS)

Natural Drainage Systems (NDS) hold and clean polluted stormwater, removing pollutants before they can reach Thornton Creek. NDS offer multiple benefits to local neighborhoods and ecosystems, including:

  • Increased landscaping

  • Lower risk of flooding

  • Creation of habitat along our streets

  • Healthier creek ecosystems

  • Traffic calming

  • More street trees


NDS installations include spongy soil and deep-rooted plants that clean and filter toxins in water. How a typical NDS planting installation changes over time: