The force generated on the tree by flowing water is at least 3.5 times the force generated in air at the same velocity. Additionally, as one tree falls over, the force of falling puts additional stress on downstream neighboring trees. A domino effect of tree toppling may occur. The flow of flood waters carry solid materials that can abrade and injure trees. The force of the moving water propels floating materials, rolls or moves solid items along the bottom of the flow, or suspends materials.
Small particles can act as sand-paper, tearing at the bark.
Wave actions can also injure stem and root crown areas. Flood flow can bring a wide range of chemicals and dissolved solids to the tree and its soil resources. Simple sediment deposition is made more damaging by organic and chemical loads from up-stream. Although most materials are extremely diluted, some materials in the water can have long lasting effects. Floods of mixed industrial areas can bring many things down-stream and in contact with trees and soil resources.