Motoki YAMANOUCHI

Problems and improvements in wave run-up assessment methods

Tokuzo HOSOYAMADA

As beaches decrease due to coastal erosion, the risk of flood damage to residences in the hinterland and traffic disruption damage from road facilities increases, making beach maintenance important.
It is essential to quantitatively evaluate and understand the safety of the backshore area and the necessary beach width, which is studied using wave run-up heights. The modified virtual gradient method has become the mainstream method for evaluating wave run-up heights, but there are concerns about the scope of application and accuracy. In addition, several calculation formulas using the modified virtual gradient have been proposed in previous studies, but all of them are for coastal structures, and it is unclear whether they can be applied to wave run-up heights. Another problem with the wave run-up heights assessment method is that it has not been determined which point should be used as the representative wave run-up height. In this study, the erosion damage caused by the bomb cyclone that occurred in December 2014 was used as the representative runup height, and changes in wave run-up height due to seafloor slope and wave conditions were confirmed using CADMAS-SURF/2D, which has many examples in research and practice as a numerical method to estimate wave run-up height on beaches. In addition, the calculation results of CADMAS-SURF/2D and the calculation results by the calculation formula proposed in previous studies are compared, and whether the calculation formula proposed so far can be applied as a method of evaluating the run-up of waves on the beach is examined. To expand the range of application and improve calculation accuracy, a new run-up evaluation method was studied.
As a result, it was suggested that the run-up formula using the improved virtual gradient is not suitable for wave run-up height evaluation on sandy beaches. Therefore, based on the calculation results of CADMAS-SURF/2D, we proposed a new formula for wave run-up height. The proposed formula for calculating wave run-up height "is applicable to a range of 1/10 to 1/50 of the seafloor gradient, which is wider than the conventional formula.