River deltas are among the most important environments on earth, housing productive ecosystems and a large fraction of the human population. The key process for delta development is the deposition of mouth bars in front of delta distributaries. Predicting mouth bar formation on marine coastlines is complex because of the interactions between waves, tides, water and sediment discharge. Here we study the effects of waves on mouth bar growth with the coupled sediment transport and wave model Delft3D-SWAN. Our results show that wave characteristics (height, period, and direction) play an important role in the formation of mouth bars. In our numerical experiments waves affect bar development in three ways: by modifying the direction of the river jet, by increasing bottom shear stresses at the river mouth, and by changing bottom friction and hence increasing jet spreading. We further show that high waves with long period prevent the formation of mouth bars; in particular, wave angles between 45 and 60 are the least favorable to bar formation, likely producing a deflected river mouth.
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