With a setback storm wall impact wave loads can occur which cause much higher loads than with a straight vertical wall. Empirical formulas for a first estimation exist, but they do not consider the geometry of the structure (height storm wall, length quay) or are not applicable for negative freeboard, or both. Due to this limitation, the main research question of this research is “What is the influence of the geometry of a retreated storm wall on top of a quay wall on the wave forcing exerted on the storm wall?”. The main method used for this research is numerical modelling using DualSPHysics (Smoothed Particle Hydrodynamics). This model is validated using a laboratory experiment. The result of the thesis is are formulae for rough first approximations of the horizontal force for the conceptual design.