Bed Strength

Bed strength (shear) represents the internal strength of the bed. It is determined by the amount of internal frictional resistance within the bed material. Bed strength depends on the sediment composition and the state of consolidation of bed. Shear strength increases when sediment grains are tightly packed together. Silt and clay particles, if present in a bed material, tend to stick together as a result of cohesive (attractive) electrochemical forces between the particles and so help in erosion resistance. Under normal flow conditions, there is a balance between the erosive power of the flow and the strength of the bed material. The changes in the channel form during major flood events, when the erosive power of the flow is greatly increased, depend on how much resistance is provided by the bed and banks. Bed erosion takes place when the bottom shear stress exceeds the strength, i.e., resistance forces, of the bed. The shear strength of the cohesive sediment bed is generally a...