When high waves and surge occur simultaneously, the flooding regime changes from overtopping by waves, combined overtopping-overflow by waves and surge, and to overflow dominated by surge. However, the modeling of combined wave overtopping and overflow, or, transient overtopping-overflow has not been well established yet. Accordingly, the present study proposed such modeling based on the full scale experimental results. The estimation of wave overtopping discharge is based on the model for seawalls installed at deep water to very shallow water including on land. The overflow discharge is estimated by a formula for weir. In the transient regime, the combined overtopping-overflow discharge is computed by properly accounting for the relative importance of wave overtopping to surge overflow. The present model was applied to idealized cases of seawall, wave and surge conditions to indicate the typical characteristics of time history of flooding discharge. In addition, the present model was implemented into a wave-surge coupling simulation model for simple conditions of bathymetry and typhoon. The results clearly demonstrated that it is very important to account for the transient phenomena in inundation simulations.
The step height of stair-type seawalls is typically set between 0.2 to 0.3 m. These short-rise stair-type seawalls have a gradual slope, which create aesthetic problems such as an increase in the construction area, as well as functional problems such as an increase in the wave run-up. To solve these problems, this study recommends that the step height increase to 1.0-1.4 m. Numerical calculations using CADMAS-SURF clearly identify the characteristics of the dimensionless run-up height and wave reflection coefficient for varying cases with step heights between 0.2 m and 1.4 m. The validity of the numerical simulations is compared to experimental results on smooth slopes by Savage and Greslou-Mahe. The dimensionless run-up height and wave reflection coefficient are unified by the surf similarity parameter. It is demonstrated that increasing the step height generally reduces these parameters and that there is an increase in reflection coefficient for the gradual slope conditions. These parameters are also associated with wave breaking morphology, step steepness and the reflection from the step surface.
Interaction between nearshore flow and river flow on sediment transport is investigated using steady flows discharged from Hamaoka Nuclear Power Plant. Aerial photos and field observations of drifting buoys show that the discharged flows change their current direction along nearshore current. We conducted laboratory experiments using fixed-bed model and confirmed that the current direction of discharged flow depends on the wave condition and the current direction changes when the wave height is larger than 1 m. The numerical model is improved to take account of the interaction between the discharged flows and nearshore current and the sediment transport and topography change in 1998 are numerically investigated. The result shows the effect of discharge flow on sediment transport appears only in nearshore region and its effect on the amount of nearshore sediment transport is little.
This is a review paper on the community ensemble estimation of the maximum storm surge heights in the three major bays of Tokyo Bay, Osaka Bay and Ise Bay in Japan. The published papers from the Journal of Japan Society of Civil Engineers since 1990 are reviewed and the maximum storm surge heights are summarized for the present climate and the future climate condition considering climate change. The ensemble average of the published research results on the maximum storm surge heights in the three major bays are equivalent or lower than current designed level for coastal protection but they will exceed in the future climate condition at the end of the century.