Numerical modelling of induced rip currents by discontinuous submerged breakwaters

Submerged breakwaters are one of the shore protective structures. Any discontinuity in these breakwaters causes changes on current parameters including speed and water surface profile. In this paper, discontinuous submerged breakwaters were modelled to investigate the changes in the wave and flow pattern. To investigate the phenomenon, three models including a shore with constant slope, a shore with continuous submerged breakwater and a shore with discontinuous breakwater were used. Extended Boussinesq Equations were used for wave generation. The results of the models showed that in the shore without breakwaters transient rip currents are produced across the shore. By addition of the breakwater, the wave breaking happens on the crest of breakwater which leads to dissipation of their energy. This in turn creates calm shore currents. However, constructing a gap in the center of breakwater causes some changes in the system of shore currents. This phenomenon generates a pair of flow vortices and a powerful return current called rip current. Rip currents not only threaten the life of swimmers, but also play an important role on the sediment transportation and erosion of the sea bed around the breakwater gap and may lead to destruction of the whole breakwater.