Floods of mixed industrial areas can bring many things down-stream and in contact with trees and soil resources. Biological and chemical hazards may be present in flood water that can injure trees and clean-up crews. Removal of soil from around roots that mechanically hold the tree erect under tension, will reduce root-soil friction, reduce soil strength, and allow for increased movement of roots and the tree. Removal of soil from around basal roots that are holding the tree erect under compression will increase the probability for root bending, shearing, fracturing, and tree toppling. Standing trees generate intense vortexes in flowing water that can remove large amounts of soil from around the stem base and from around large roots.
Erosion can make the tree much more susceptible to wind and water pressure failures.
Erosion can also lead to tree structural failure after flooding when normal moisture conditions have been regained. Structurally unstable trees can be at great risk for unexpected collapse. Flood clean-up operations can be endangered from damaged trees, as can people and property around the structurally damaged tree. The risks associated with structural problems can be compounded by other types of damage, by time, and by other site changes. Several years may be needed to fully determine the extent of flood damage to trees and any increased liability risks.