The woes of storm water

Trees intercept storm water
Trees intercept storm water

What happens to all the rain that falls on streets, driveways, rooftops and other developed land? It’s one of the most widespread challenges to water quality in Washington state, and it’s called storm water runoff. It carries oil, grease, fertilizers, soaps and waste from pets and failing septic systems into streams and other bodies of water.

DNR works to clean up and restore natural areas in Puget Sound communities, because the clean water that originates in the upland forests we manage can become polluted as it flows through urban and suburban areas.

One of the best ways to mitigate the negative impacts of urban and suburban storm water runoff is to reduce how much of it ends up in natural waterways. Trees and shrubs are part of the solution.

Since October is Urban and Community Forestry Month, it’s an excellent time to recognize the many benefits that trees provide, including reduction and filtration of storm water runoff, because trees:

  • Slow down runoff rates by intercepting rainfall in their canopies.
  • Reduce runoff volume by absorbing storm water through their roots.
  • Absorb and store pollutants carried by storm water, transforming them into less harmful substances.
  • Create healthy soil conditions that allow rainwater to filter into the soil so that less flows down streets, sidewalks, gutters and storm sewers.
  • Reduce erosion of streambanks and soils.

Here’s what you can do to help the trees in your community do a better job of filtering and managing storm water runoff:

  • Decrease the amount of hard surfaces (like concrete) that block water from soaking into the soil.
  • Advocate for planting more trees and vegetation in your community.
  • Preserve healthy, established trees through proper maintenance and care.
  • Minimize the clearing of trees and vegetation ­– you’ll also help reduce soil erosion.
  • Avoid over-fertilizing or over-watering your trees and lawn.
  • Route excess storm water to a natural retention area, such as a vegetated area with healthy soil which can filter out pollutants, reduce runoff rates and volumes, and prevent soil erosion.
  • Retrofit parking areas and other locations with extensive hard surfaces with new plantings of trees, shrubs and other plants — strategically located, they can intercept storm water and allow it to filter into the ground.

For more tips and ideas, visit DNR’s Urban and Community Forestry Program, which operates with support from the US Forest Service.