Sediment transport initial conditions

Initial conditions need to be specified for the bed layers and cohesive sediment concentrations. Initial conditions only apply if:

• There is at least one cohesive sediment fraction, and/or
• There is at least one sediment layer

No initial conditions are specified for the initial non-cohesive sediment concentrations, as these are set internally equal to the equilibrium concentrations initially.

Initial cohesive concentrations do not necessarily matter in a model, especially if it starts at low flows and runs long time-scales compared to the influence time-scale of the initial concentration.

The initial conditions for the bed layers are important, and the process involves setting the initial thicknesses of the layers along with particle size distributions for the layers.

There are many tricks that can be used:

• In many cases, one does not have detailed information about the bed layers.
• It is possible in a 2-layer model to only specify a thickness of one of the layers along with a particle size distribution; the bed layer model will automatically balance the active and passive layer thicknesses during the first time-step.
• The depositional problems the initial bed composition may not be important.