Sediment removal¶
Basins and structures can act as "sediment traps" because the water flow kinetic energy and turbulence (hence, dynamic forces acting on sediments) in the basin or before the structure are much lower than in the river branches or sewer links.
Only the bed load is affected by sediment removal, and hence only non-cohesive sediment fractions are affected.
The sediment removed can be reported in the ST output file as removed sediment load or total removed sediment mass (instantaneous or accumulated) for each fraction separately and accumulated for all fractions.
Sediment removal in nodes¶
MIKE 1D does not simulate sedimentation in basins and manholes. However, effect of basins on sediment transport (non-cohesive bed load only) may be emulated by defining a sediment removal efficiency in individual basins. This function removes the specified fraction of the inflowing non-cohesive (ST transport) sediments. The efficiency is defined as:
Equation: Sediment trap efficiency of a basin.
Where:
- \(E\) — sediment trap efficiency
- \(w\) — fall velocity
- \(Q\) — discharge into the node
- \(A\) — surface area of node
- \(n\) — turbulence constant indicating the settling performance of the basin
The turbulence constant takes the following values:
- \(n = 1\), for poor performance
- \(n = 3\), for good performance
- \(n > 5\), for very good performance
- \(n = \infty\), for ideal performance
The removed sediments are taken out of the computations. No morphological modelling takes place of the removed (deposited) sediment and it is not possible to re-suspend this sediment.
Sediment removal in structures¶
Structures such as weirs can act as efficient barriers for bed load transport, as the weir crest level can be significantly higher that the reach invert level. This means that significant part of non-cohesive sediment cannot be transported over weirs. This is typically applied in sewer context.
MIKE 1D simulates effect of weirs on bed load transport by defining a constant sediment removal efficiency factor or removal efficiency factor as function of weir discharge.