Additional notes on impact forces:

• The value for the velocity of flood-borne debris is the same as in hydrostatic force computations
• The type of construction (e.g., timber, concrete, steel) is an important factor in impact force calculations
• American Society for Civil Engineers (ASCE) 7-10 Commentary contains guidance on calculating impact forces and selecting proper size of debris
• FEMA P-259, Equation 4-11, is simplified from ASCE 7-10 Commentary using reasonable assumptions.