Assessment of a Measure for Water Exchange Strengthening of Artificial Headland Bays Based on Shoreline Change and Flushing Time

Artificial headlands are used around the world to form headland bays to contain beach materials. However, the artificial headland would weaken the water exchange in the bay and in some cases would make the water quality deteriorate. In this paper, we propose reserving a tidal channel in the landward end of the artificial headland, thus enabling the tidal current to pass through the channel, as a solution. The effects of the tidal channel on the weakening of beach protection and the strengthening of water exchange were investigated via numerical studies based on a beach nourishment project. A shoreline change model was set up to investigate the weakening of the beach protection. Four project schemes were simulated, and the results indicated that weakening of the beach protection is acceptable and the response of the shoreline to the tidal channel is influenced by the state of the beach. A three-dimensional (3D) flow model and a 3D constituent transport model were applied to evaluate the strengthening of water exchange using flushing time as the indicator. The results indicate that the reservation of the tidal channel induces an approximate 50% reduction in flushing time. The specific reduction amount of the flushing time is influenced by the length of the tidal channel, the tidal condition, and the direction of the artificial headland. The conclusions suggest that the tidal channel is a feasible and effective measure to strengthen the water exchange in an artificial headland bay at the cost of an acceptable loss of beach protection effect.