Beach response to breakwater layouts of drainage pipe outlets during beach nourishment

Managing drainage pipes to optimize beach nourishment is a complex problem. In this study, the ‘salient’ landform is explored as a feasible plan that considers beach nourishment and breakwater geometry of the drainage pipe outlets. The XBeach model was used to establish an idealized model for analyzing the beach response to three typical breakwater layouts (straight, landward convex, and seaward convex). The seaward convex breakwater layout was found to be the most effective option because it can accumulate the largest volume of sediment behind the structure. The seaward convex layout was also used to analyze the beach response to incident wave angles ranging from 0° (normal to the shore) to 60°. As the incident wave angle increases, the volume of sand salient accumulated in the leeward of the breakwater and the flow speed in the cross-show direction gradually decrease, while the wave height and the flow speed in the along shore direction gradually increase. However, there is a critical angle of approximately 50° at which opposite trends of changes in bed level, wave height and Eulerian flow occur.