The Layers layout define the number of layers used in the simulation:
· Active and passive layers: this option requires at least two sediment fractions
· Active layer only: this option is always available
· Fully alluvial model (no layer): this option can be selected when only one sediment fraction is simulated and that fraction must be non-cohesive
The bed material may be represented by two layers, an active layer in which sediment transport occurs overlying a passive layer. Each layer is divided into the number of fractions specified in the Sediment fractions definitions menu.
Target thickness of active layer
The following parameters are required for the target thickness of the active layer. Global values are mandatory and applied throughout all calculation points in the river network unless local values have been defined. Local values may be applied at specific locations defined by Branch name and Chainage. The target thickness is calculated as a factor on the current water depth, though always within the range defined by the minimum and maximum value. To give it a fixed value, set Minimum and Maximum values to the desired fixed value.
Factor on depth
The factor to multiply on the current water depth to get the target thickness of the active layer during simulation.
Minimum value
The minimum allowed thickness of the active layer during simulation.
Maximum value
The maximum allowed thickness of the active layer during simulation.
The morphological update method is applied only when the morphological update is included, in the General parameters menu.
A global method must be specified. Three options are available:
· Horizontal distribution: sediments rest on the cross-section's bottom with a flat sediment surface. Primarily for use in cross sections with a fixed underlying bed, e.g. bottom of cross section made of concrete or sediment transported in pipes.
· Uniform distribution: erosion and deposition are evenly distributed along the cross section.
· Proportional to depth: erosion and deposition are proportional to water depth. This method uses the Floodplain level definition, specified in the cross sections. Primarily for use in cross sections with floodplain to exclude the floodplain from sediment transport calculation.
The global method is applied throughout all calculation points in the river network unless local methods have been defined. Local values may be specified in the table. Local values are applied at specific locations defined by Branch name and Chainage.