Number of fractions
At least one fraction must be specified. The number of fractions can be controlled using this parameter, or by adding or removing lines in the table from the Sediment fractions definitions menu. When this number of fractions is reduced, the last rows of the table are removed accordingly.
When morphological update is not included in the simulation, the Sediment transport module only computes a transport capacity, without any effect on the bed level.
When morphological update is included, the bed level is continuously updated depending on local erosion and deposition, and therefore affecting the calculated hydrodynamic conditions. The method used to update the bed level is specified in the Bed parameters menu.
Note: the morphological update affects the flow area, flow width and hydraulic radius values used in the hydrodynamic simulation, but it does not directly update the geometry of the physical cross sections. Therefore, the effect from the morphological update can be seen in the corresponding hydrodynamic result items (flow area, width, radius), but not on the shape of cross sections shown in the result files.
Maximum concentration allowed due to erosion
This parameter limits the erosion that can take place during a morphological time-step in such a way that the erosion cannot occur if it causes the sediment concentration to go above the specified maximum value. The limit applies to both bed load and suspended load.
For bed load it is applied in the form of translating the maximum concentration into a change in the sediment mass in the bed during the morphological time-step.
For suspended load the limit is used directly on the erosion function appearing on the right-hand side of the advection-dispersion equation.
The maximum concentration allowed due to erosion parameter is critical for morphological stability, but should be used with caution, as very low limits will suppress physics.
Skin friction model
The following options are available for the skin friction model:
· Total friction
· Law of the wall (full depth)
· Law of the wall (skin friction depth)
Egiazaroff hiding function
When multiple sediment fractions are simulated, the Egiazaroff hiding function can be applied.
Kinematic viscosity
The kinematic viscosity is used for calculation of the settling velocity for the sediment.
d90/d50
The d90/d50 value is required when modelling a single fraction.
