The São Francisco River mouth is undergoing a severe erosional process that has caused the destruction of a village and the partial immersion of a lighthouse constructed in 1856. The present work comprises an historic time evaluation of this phenomenon based on the analysis of the sediment dispersion patterns caused by waves along three distinct shoreline traces. For this, we define a wave climate model based on the construction of refraction diagrams, which are assumed to be valid for the three shorelines. The resulting sediment transport patterns obtained by numerical modeling from the refraction diagrams—taking into account the angle of approach and the wave height along the coast—allow us to establish a first-order correlation between coastal dynamics and erosion phenomenon. The results also suggest that a permanent reduction in the solid river discharge, in response to the construction of large dams, probably will have two direct consequences in the river mouth region: (i) a chronic shoreline erosion downdrift of the mouth and (ii) a progressive deflection of the mouth in the downdrift direction.