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Large Woody Debris (LWD)

What is large woody debris?

Large woody debris (LWD) refers to the fallen trees, logs and stumps, and root wads, found near or within stream and river channels, as well as along the edges of lakes and Puget Sound.

Why is large woody debris important ecologically?

LWD helps stabilize shorelines and provides vital habitat for salmon and other aquatic organisms. Preserving and even increasing the amounts of LWD in streams and along shorelines is important for keeping our aquatic ecosystems healthy, in addition to improving the survival of native salmon and wildlife.

Large Woody Debris

Some key benefits of LWD to fish and other aquatic biota include:

  • Provides refuge for juvenile and adult fish at a wide range of river flows, such as flood events
  • Creates pools for juvenile fish and hydraulic complexity and roughness along the river bank
  • Provides food sources and habitat for aquatic insects and wildlife along shorelines
  • Stabilizes shorelines and reduces excessive streambank erosion

Large woody debris is delivered to aquatic ecosystems in various ways:

  • Wind-throw: when wood is blown down in large wind storms
  • Streambank erosion
  • Beaver activity
  • Trees dropping branches
  • Mass wasting events or landslides

What interferes with the recruitment of large woody debris?

  • Shoreline armoring can keep LWD from reaching streams or may prevent it from lodging in one place
  • Washout due to high storm flows in urbanizing areas with excessive stormwater runoff
  • Reduced water flow (through diversions or withdrawals)
  • Removal of shoreline vegetation, especially on unstable slopes, can prevent the delivery of wood to shorelines
  • Removal for firewood or other human uses
  • Removal when it poses a safety concern