Bed parameters influence the processes going on near or at the bed.
Porosity
Ripples
Critical Shields parameter
Inertia coefficients
The sediment porosity controls the Littoral drift output as sediment drift is given in volume.
The output from a Transport in point defines transport capacity which is given in solid material.
The effect of ripples on the bed shear stresses may be included.
The four constants C1, C2, C3 and C4 are used for assessing the dimensions and the effect of wave ripples, if any. It is usually not recommended to change the default values.
The criterion for sediment in movement is that the critical shear stress for erosion is exceeded corresponding to the driving forces exceeding the stabilising forces. The default value is 0.045.
In case of shingle sized material, the inertia forcings may influence the dynamics and the critical Shields parameter is calculated internally based on the inertia coefficients. For sand particles, the critical shear stress for erosion is constant throughout the simulation.
When simulating shingle sized material, the individual grains are considered to be of a size where inertia will begin to have an impact of the movement of the sediment.
You have to define the following five inertia coefficients:
1. Dynamic friction coefficient
The dynamic friction coefficient, md, is related to the dynamic friction angle for the bed sediment, md = tan(fd).
2. Static friction coefficient
The static friction coefficient, ms, is related to the static friction angle (angle of repose) for the sediment, ms = tan(fs).
3. Alpha coefficient
The Alpha coefficient is a non-dimensional coefficient.
4. Drag coefficient
The drag coefficient, cd, is about 1.4 for shingle sized sediment.
5. Hydrodynamic mass coefficient
The hydrodynamic mass coefficient, cm, is about 0.5 for shingle.