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Health / Safety

Flood-damaged trees cause safety concerns

September 18, 2013

As many communities along the Front Range and in northeast Colorado deal with the aftermath of recent flooding, one concern that should not be overlooked is the risk of trees falling due to the erosion caused by rushing water.

Ash trees surrounded by flood waters. Photo taken by the City of Boulder.Community Forestry Program Manager Keith Wood of the Colorado State Forest Service said heavy flooding can soften soil and wash it away from roots of trees, weakening tree stability and eventually killing any roots that become exposed to the air. Conversely, other trees may slowly weaken or die if their roots have been in standing water for long periods of time or are smothered by a thick layer of newly deposited soil.

Loss of root structure

“In flood-impacted areas, there will be trees at risk of falling over due to the loss of root structure, which presents a safety risk to affected communities,” said Wood. “Besides the immediate threat, weather events such as early winter snows and down-sloping winds create an extended risk of weakened trees falling.”

Evaluating tree health concerns

  • Look for signs that a tree has been compromised and may require an inspection, which include a new lean to the tree, mounding of soil near the trunk, cracks in the soil as it dries out or obvious soil grade changes near the tree.
  • Use only an insured, International Society of Arboriculture-certified arborist to inspect trees for flood damage. Professionals often are listed in the phone book under “tree services,” and a listing of ISA-certified arborists can be found online.
  • Avoid approaching trees adjacent to creeks, ditches or areas where flood waters are receding.
  • Keep an eye on any trees of possible concern for the next few months, especially in riparian areas, and be aware of the lingering risk of falling trees, especially in high winds.
  • Look out for broken or cracked branches caused by water pressure, water weight or previous recovery and rescue efforts.

To deal with trees of concern, arborists may recommend trenching to remove standing water, removing excess soil on top of root systems and replacing soil lost over root systems.

For more information about tree care and protection, visit the Colorado State Forest Service website.