A numerical simulation of the shape of submerged breakwater to minimize mean water level rise and wave transmission

Abstract: It has been widely reported that coastal erosion causes problems worldwide. In order to solve these problems, breakwaters have been constructed in such regions. However, it is also a fact that breakwaters adversely affect the environment and scenery. To be able to prevent coastal erosion, while still preserving the environment and the view, submerged breakwaters have been introduced. However, submerged breakwaters have been shown to have a major flaw: they tend to increase the mean water level behind the breakwater, which in turn is a factor causing further erosion of the coast. One example of such a scenario is the west coast of Niigata, Japan. In order to minimize this mean water level rise, a number of studies have been carried out, but most of them do not reduce either the mean water level or the wave transmission sufficiently. Therefore, this paper aims to develop the shape of the submerged bank to minimize both the mean water level rise and the wave transmission. A numerical calculation in two dimensions has been carried out under the assumption that the submerged bank is of great length. Calculations are done for both submerged banks modeled after existing banks in Niigata, and for long, low submerged banks with several vertical impermeable plates. The obtained results were compared to each other in regards of spectrum analysis, mean water level, significant wave heights behind the bank, and significant wave height in long waves. The newly-introduced submerged bank showed high efficiency in minimizing the mean water level and wave transmission. Furthermore, the submerged bank could minimize the transmission of long waves, which shows great promise for future implementation.