Fundamental flow characteristics in the surf zone of spilling (SP) and plunging (PL) breakers are compared using a well-validated numerical model named COBRAS. The main objective is to investigate how beach slope affects flow characteristics (streamline topography, vorticity evolution processes, TKE dynamics and reverse flow) in the surf zone of plunging (PL) and spilling (SP) breakers. The major results are of four categories: (1) the streamline topography of PL waves is mostly similar to that of SP. For both types of breaker, a convergent stagnation point (CSP) always appears in the offshore direction after the generation of a divergent stagnation point (DSP). The location of a DSP is generally underneath the front face of wave crest. Both DSP and CSP move to the inner surf zone following wave propagation. (2) the main difference of vortices evolution is that clockwise (CW) vortices after wave breaking are stronger for PL waves but mild for SP waves . The CW vortices of SP decay upstream directly but those of PL waves advect toward the bottom slope and then degenerate upstream. (3) The TKE generated by PL waves is much larger than that generated by SP waves. The distributions of generated TKE values of SP and PL waves are similar to the corresponding vortex motions. (4) The maximum magnitude of reverse flow in surf-zone of PL waves is around 1.4 times that of SP waves.

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