Sediment flushing is one of the proposed methods for preserving the storage capacity of dam reservoirs. In flushing with water level drawdown, the incoming flood erodes a flushing channel in the deposited sediment. Flow pattern as well as flushing channel formation procedure in shallow reservoirs is complex phenomenon due to the dynamic interaction between flow field and bed changes. In the present study, the flow field and flushing channel formation procedure were investigated in various shallow reservoir geometries using physical experiments and numerical simulation. A fully 3D numerical model which applies Finite Volume Method (FVM) was utilized. Reasonable agreement was found between the numerical and experimental outcomes. The results would be useful to understand the influence of geometry on flow pattern and flushing process to conduct more efficient sediment management strategies.