Embankment breaching is a composite process coupled by hydraulic processes and sediment transport processes. Erosion is the link in the interaction between breach flow and embankment material. Surface erosion starts in the initial breach phase and triggers the initial damage of the embankment. As the surface erosion develops completely, the headcut erosion leads the breaching process by cutting the embankment slope and deepening the crest level finally. The helicoidal erosion undermines the side slopes of the breach and widens the breach in lateral direction by triggering the breach side slope to collapse. In order to reduce the scale impacts in the lab and defects from the prototype experiments in the field, there were 5 runs of large-scale sediment (sandy clay) models (2m high, 3m long) conducted in the flume (3m×3m×60 m) to investigate the cohesive embankment breaching mechanism. The breach hydrodynamic processes (discharge, water level, velocity) were measured in the experiments and topography changes were recorded with 3D scanner every 5 minutes. The results for each runs of the breach experiments were good validations of the 3 types of erosion (surface erosion, headcut erosion and helicoidal erosion) in the cohesive embankment breach.