Coastal Engineering Journal

Wave overtopping on gentle slope seawalls for both smooth and stepped front faces was investigated in a laboratory wave flume. Overtopping rates were measured by a catchment basin placed behind the seawall. Overtopping velocity and water depth at the top of the seawall were simultaneously measured by using a Laser Doppler Velocimeter and a wave gage. It was found that the velocity of overtopping water has a sharp peak just after initiation of each overtopping event. The water depth on the seawall crown shows relatively gradual decrease.

A numerical model of three-dimensional Large Eddy Simulation was developed for evaluating the instantaneous overtopping discharge and compared to the experimental results. The calculated root-mean-square value of water surface elevation at the toe of the seawall agreed very well with the measured value, but large discrepancies were found for individual wave deformation in some waves. The magnitude of the calculated velocity on the top of seawall was generally smaller than that of the measured velocity. The calculated volume of the overtopping water was between the volumes measured for the smooth seawall and the stepped seawall. Since the two-dimensional Large Eddy Simulation model far overestimated the overtopping volume, it was considered that appropriate representation of three-dimensional large eddies generated by wave breaking is important for wave overtopping evaluation.

An X-band marine radar system has been employed to determine shoreline positions and intertidal foreshore slopes over an area 1.9 km in the longshore direction at the research pier HORS in Hasaki, Japan. The X-band marine radar is an imaging radar that provides instantaneous distributions of wave crests and shorelines along the shore. Time-averaged radar images were analyzed to estimate the horizontal positions of shorelines. Simultaneously, the water surface level was measured at the pier and at the fishery port nearby to determine the elevation of the shoreline. Radar measurements were conducted from high to low tide or vice versa to trace the bottom profile and estimate the foreshore slope in the intertidal range. The horizontal positions of the shoreline were measured within an error of 10 m. The change of shoreline positions and intertidal foreshore slopes after attacks of high waves is depicted to demonstrate the potential of the radar measurements in capturing essential characteristics of coastal morphology.

This paper deals with the seawater exchange caused by the density gradient between the outside and inside of Ohfunato Bay using a density profile around the mouth of the bay and velocity profile above the breakwater mound which has been constructed on the bottom of the bay mouth. The field observations are carried out in order to realize seasonal characteristics of current structures and water qualities behavior in Ohfunato Bay. As a result, it is revealed that the mechanism of seawater exchange is greatly influenced by the density intrusion depending on the longitudinal density gradient. When the density of the outside of the bay is smaller than that of the inside, the seawater exchange occurs in the upper layer and cannot be expected in the lower layer. On the other hand, when the density of the outside bay becomes bigger than that of the inside bay, the seawater exchange is accelerated by two types of density currents. One is intrusion of the outside bay water, and the other is outflow owing to an entrainment above the mound.

Over the last decades, the Polish coast, about 500 km long and predominantly featured by sandy, low-lying beaches, has been exposed to various threats resulting from intensified climate change and Accelerated Sea-Level Rise (ASLR). This has manifested itself in the growing intensity of shoreline, dune and cliff erosion and by the increasing necessity of their protection.

The current study is both a summary and an extension of the existing Polish studies and analyses on the present and predicted influence of ASLR on the coast. First, the Polish coast was divided into three basic area types (AREA I, II, III) according to their geographic and socio-economic background. Then, two different scenarios of accelerated sea-level rise (ASLR1 — 30 cm/100 yrs and ASLR2 — 100 cm/100 yrs) were assumed. After that threats of land loss and the risk of its temporary or partial inundation was analyzed in connection with the assessment of the material and social costs and losses. These analyses were made within the framework of two adaptation scenarios, i.e. retreat (do nothing) and full protection.

The performed analyses have shown that the greatest threat of partial or full land loss and the associated material and social costs are expected to occur in two regions of the Polish coast. One of them is situated in the eastern sector of the Polish coast and covers the agglomeration of Gdańsk and the Żuławy polders. The other is located in the west and comprises low-lying areas around the Szczecin Lagoon and the vicinity of the Odra river mouth. These areas both require intensive care and protection efforts.

A particle method, or a gridless Lagrangian method, shows the high performance in describing the complicated behavior of water surface with the fragmentation and coalescence of water. In this paper, a wave overtopping process on a vertical seawall is numerically simulated on the basis of the Navier–Stokes equation with surface-tension term, which is discretized by the MPS (moving particle semi-implicit) method belonging to the category of the particle method. An improvement of the listing process of neighboring particle is introduced to reduce the computational load. Wave overtopping process in the experiments are well reproduced by the MPS method. The predictions of the MPS method of the overtopping volume agree well with the experimental results.