Determining the Zone of Scour

The movable bed limits in the HEC-RAS sediment transport module define the transition between incision and scour. Inside of the movable bed limits, the channel is modified by the movable bed model (incision and deposition translated into vertical node movement). Outside of the movable bed limits, scour equations are used⁵. The model is very sensitive to the selection of these limits.

The scour equations in the USDA-ARS BSTEM that are implemented in HEC-RAS compute lateral bed change of the wetted nodes outside the movable bed limits for cohesive or cohesionless soils based on a radial shear distribution.