Impact loads are imposed on the structure by objects carried by moving water. The magnitude of these loads is very difficult to predict, but a reasonable allowance must be made for them in the design of retrofitting measures. Loads can be classified as:

• No impact, which occurs in areas of little or no velocity or debris
• Normal impact, which are isolated occurrences of typically sized debris or floating objects striking the structure
• Special impact, which occurs when large objects or conglomerates of floating objects, such as ice floes or accumulations of floating debris, strike a structure
• Extreme impact, which occurs when large, floating objects, such as runaway barges or collapsed buildings, strike a structure