How Our Trees Clean Our Water

Published on July 14, 2017

Trees as a Filter

Arlington County recently installed its first forest buffer as a stormwater Best Management Practice (BMP) at Bluemont Park’s new baseball field. This forest buffer not only looks great, but also serves an important function for this park and our community.

To help improve the Chesapeake Bay Watershed, and the water we depend on, trees are being used on larger projects that allow water to flow into a forest or forest buffer. The trees improve our water in many ways, along with providing other benefits of air pollution control, shade, beauty and wildlife benefit.

Bluemont Forest Buffer
Bluemont Forest Buffer

The First Rain: Interception and Evaporation

Every tree catches the rain as it comes down, but did you know a mature White Oak (Quercus alba) can intercept up to 12,010 Gallons of water every year? That’s just a single tree! This water stays in the leaves until it’s absorbed by the tree or evaporates to cool our air. This is the first line of defense, as this prevents this water from needing to be piped or treated by other stormwater infrastructure. According to our i-Tree Eco study, our trees in Arlington alone capture 80,267,230 gallons every year!

Keeping it in the Soil and Filtering: Infiltration and Storage

Trees are designed by evolution to make the best use of every drop that falls on their canopy. Their leaves and branches act like a giant capturing device to get precious water to the tree’s roots. This helps trees provide one of the greatest stormwater benefits: infiltration and storage. Through filtering the water with their roots and soil, pollutants get trapped and diluted which reduces the impact of water pollution.

Additionally, storing all this water makes it available for the tree and other plants around it. This stored water can then be used to grow the tree and evaporate this water back into the air, once more preventing it from impacting our stormwater system.

Stormwater Benefits of Trees
Stormwater Benefits of Trees: Source: Deeproot

Forest Buffers as a Stormwater Device

In the case of Bluemont’s baseball field, there were some restrictions to using this tool, but it was perfect for this project. These are some of the restrictions to using forest buffers for stormwater credit:

  • You need a fairly flat slope and space to accommodate the water to slowly flow through
    • Very flat slopes (1-4%) can use a 35 ft buffer
    • Moderately flat slopes (4-6%) need 50 ft
    • Steeper slopes (6-8%) need 65 ft
  • Soils must be able to drain and store the water

Wider Benefits

These solutions can have a great positive impact on our community and has many benefits over traditional stormwater infrastructure:

  • This technique is a non-engineered, nature-based solution to stormwater
  • Near streamsides, forest buffers can significantly improve tree canopy and our natural habitat
  • Lower cost than engineered solutions, in most cases

Learn More

How Trees Tame Stormwater by the Arbor Day Foundation

Benefits of Forest Buffers by the Chesapeake Bay Foundation

Forest Buffers presentation to the Urban Forestry Commission

The streamside Forest Buffer. Source: USFS(GIF, 351KB)
The Streamside Forest Buffer. Source: USFS

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