I am simulating a sill downstream bridge piers in 2DH simulation with crest level of the undisturbed bed.
I simulated this sill in three different ways
1- by fixing the cells in the cross-section of the weir (no erosion to the cell) 2- using a weir (2D weir model) 3- using a local weir
Most of this sill is under the bed in the cross-section of the river as I simulated it in a cross-section where a central bar in the middle and scour on both sides to study its effect in mitigating the bars formed and redistribute the bed.
But there is something strange to me. In some simulations most part of the weir is covered under the bed and however that there is a water head of around 3 cm away from the bridge piers effect. I notice this when I simulated it as a 2D weir and a local weir as well.Only local weir simulation gives me satisfying results in 2D but when I fixed the bed or using a local weir it did not give me good results was thinking about the shortcoming of using these structures because they mentioned in the manual they are simulated by overall influence by the energy losses due to the weir. These energy losses are described as an additional quadratic friction term in the momentum equations.