Takashi Tamada

Wave runup and overtopping at seawalls built on land and in very shallow water

AbstractThe current study proposes prediction formulas both for random wave runup and mean overtopping discharge at seawalls constructed on land or in very shallow water. Although several existing formulas for runup and overtopping use the incident wave characteristics at the toes of seawalls, this study adopts the equivalent deepwater wave characteristics and an imaginary seawall slope for easy application of the formulas, especially in relation to seawalls constructed on land. The prediction formulas for overtopping use the predicted runup values. For the wave runup prediction formulas two sets of experimental data are used; i.e., a new set of data and the data obtained in a previous study. For the wave overtopping prediction formulas, the experimental data measured in a previous study are used. Comparisons with measurements show good performances of both new prediction methods.

Analysis of Climate Change Effects on Seawall Reliability

Crown heights of seawalls should be designed to suppress overtopping discharge to a permissible level. The permissible level is determined from viewpoints of the structure types of coastal seawalls and hinterland use. It is usually difficult to design the crown heights of seawalls, especially in the present time where climate change due to global warming is expected. This study analyzes climate change effects such as sea level rise (SLR) and increase of waves and surges on the failure probability of seawalls under various conditions of crown height, toe depth and slope by using a Level III reliability analysis. It was found that the difference of SLR trends (fast, medium or low) has less impact on overtopping rates than the differences in wave height change for a seawall at a target location.

RUNUP FORMULATION FOR SEAWALLS NEAR SHORELINE

The height of seawall is determined based on allowable wave overtopping rate or wave runup height for the design of surge and wave prevention facilities. Although a design method based on wave overtopping rate takes into account of wave randomness, a design method based on wave runup height does not consider the wave randomness but uses equations and figures obtained from regular waves in Japan. Therefore, a unified prediction formula for random wave overtopping and runup is required for establishing the design scheme of seawalls. This study proposes prediction formula for random wave runup heights for seawalls with composite cross section installed near shoreline.

Applicability of movable bed model for tsunami in tsunami disaster reduction in rivers

Using the numerical analysis of tsunami run-up and inundation, safety assessment of river levee, damage prediction by tsunami inundation and countermeasures for the safety of residents are considered. For the past examination, fixed bed model were used for the numerical analysis even in the area of river mouth where the sand bar is well developed and the reflection and dissipation of tsunami wave and sand deposit in the channel were prominent. In this study, movable bed model for tsunami wave proposed by Takahashi et al.(1999) was used to analyze the dominant factor for the computational accuracy in order to apply this model to tsunami run up in the river. Kiku-river was chosen for applicability evaluation and tsunami prevention measures were considered through the results obtained from proposed model.