Numerical modeling of Sediments flow in a desilting chamber (settling basin)
 

I am doing the numerical modeling of sediments (checking the effectiveness of desilting chamber, whether the design and shape of the desilting chamber can effectively settle the sediments of size more than 0.2mm or not, so to reduce the impact on runners of the Hydropower plant). The water is coming from the intake of the concrete gravity dam to the desilting chamber. The water in the dam is the direct runoff river from the mountains that contains sediments of any sizes and types.

I am not sure about how to input the sediments data or choose the right physics model to get the correct results. Do I use multiphase models, if then how to proceed with it?

I'd say - it should be either Eulerian-Eulerian Continous-Dispersed (full Eulerian, not DMP, not MMP) model or DEM (probably with Coarse Grain approach).

From what I can imagine your dimensional and time-scales are expected to be pretty large (to run it transient) - so Eulerian-Eulerian might be a better option because there is a chance of convergence for steady case, while DEM is purely transient.