Numerical Study on the Flow and the Sedimentation During 2008 Flood in the Koshi River in Nepal

This study has attempted to replicate the flooding and the sedimentation during the 2008 flood by using a numerical model. A two-dimensional morphodynamic model, which can treat the bedload and suspended load transport of non-uniform sediment, has been applied to simulate the flood flow and the sediment transport induced by the levee breach. By using this model, we have investigated how this flood propagates on the floodplain and how much sediment was supplied from the levee breach point. The volume of the flood flow and the sediment transport into the floodplain has been estimated. In addition, we have conducted a case study, which focuses on the effect of the bed level difference between the riverbed and the floodplain to the volume of the flooded sediment and the bed evolution dynamics in the Koshi River. The proposed model predicts the flood discharge due to the levee breach reasonably well; however, the amount of the floodplain sedimentation appears to be under-predicted. The result also reveals that the bed level difference between the riverbed and the floodplain strongly affects the sedimentation volume on the floodplain and the channel evolution dynamics in Koshi River