Hiroki Kikuchi

Study on the deformation of run-up waves near coastal shorelines using a numerical wave model

Tokuzou Hosoyamada

The west coast of Niigata has experienced significant coastal erosion since the late Meiji era. The recession of the shoreline has subsided as a result of the adoption of the surface protection method as a countermeasure, but regular monitoring and maintenance are still being carried out for coastal protection.
The phenomenon in which a wave goes over the shoreline and rises on land is called run-up wave. Run-up wave is one of the causes of beach erosion on the foreshore and is important for coastal management. In the past, laboratory experiments were conducted to calculate the wave run-up height, and formulas and charts were proposed based on the experiments. On the other hand, the VOF method, which is based on the Navier-Stokes equations, has become a popular method for numerical calculations, and in principle it is the closest to the essence of fluid flow calculations. However, some problems have been reported, such as the overestimation of calculation results under certain conditions. In this study, the run-up wave is calculated using the numerical wave hydrograph CADMAS-SURF with the VOF method, and the results are compared with the measured data and the improved virtual gradient method to investigate the accurate prediction method of wave run-up.
The improved virtual gradient method was programmed to investigate the behavior of the wave run-up height when each variable was changed. As a result, it was confirmed that the launch height became excessive when the slope of the seabed became slower than 1/30, although the behavior was generally in accordance with the actual phenomenon.
The effects of various parameters of CADMAS-SURF were investigated.  As a result, the turbulence model, the grid spacing, and the setting of the difference scheme were found to be particularly influential, and the optimal calculation conditions were found.
As a result, the difference between the measured and calculated values was generally kept within 10%.  The difference between the measured and calculated values was generally within 10%. Since the improved virtual slope method is easy to use, it is concluded that the improved virtual slope method is basically appropriate for calculating the wave run-up height to facilitate coastal management.