Coastal Dikes Research Articles

Long–wave forcing by the breaking of random gravity waves on a beach

This paper presents new laboratory data on long-wave (surf-beat) forcing by the random breaking of shorter gravity water waves on a plane beach. The data include incident and outgoing wave amplitudes, together with shoreline oscillation amplitudes at long-wave frequencies, from which the correlation between forced long waves and short-wave groups is examined. A detailed analysis of the cross-shore structure of the long-wave motion is presented, and the observations are critically compared with existing theories for two-dimensional surf-beat generation. The surf beat shows a strong dependency on normalized surf-zone width, consistent with long-wave forcing by a time-varying breakpoint, with little evidence of the release and reflection of incident bound long waves for the random-wave simulations considered. The seaward-propagating long waves show a positive correlation with incident short-wave groups and are linearly dependent on short-wave amplitude. The phase relationship between the incident bound long waves and radiated free long waves is also consistent with breakpoint forcing. In combination with previous work, the present data suggest that the breakpoint variability may be the dominant forcing mechanism during conditions with steep incident short waves.

HISTORICAL BEACH EROSION OF SOUTHWEST SURUGA COAST AND SHORE PROTECTION

Beach changes of the southwestern part of the Suruga coast located in Suruga Bay were investigated through the comparison of aerial photographs, historical photographs showing the damaging process of coastal dike in 1972 and photographs taken in the field observation on April 24, 1999. On this coast, southwestward longshore sand transport dominated before the construction of the breakwaters of Yoshida Port. After its completion, the shoreline northeast of the breakwater approached stable condition. In this area, coastal dike was destroyed by wave action in 1972 and new coastal dike was built landward of the original position. Due to this activity, present shoreline became stable with seasonal variations. On the southwest side of the harbor, beach was eroded by longshore sand transport and measures by detached breakwaters were taken. This further induces beach erosion and steepening of the foreshore at further southwest coast.

EXPERIMENTAL STUDY ON DAMAGE STRUCTURE OF A LAYER ARMOR BLOCK OF GENTLE SLOPE-TYPE COASTAL DIKE

The report shows the damage structure of a layer armor block of gentle slope-type coastal dike by the model tests on stability. According to the experimentation this time, it has been found that there is a difference of tendency between Hudson's experimental results and a layer armor block's experimental results.

Response of Coastal Dike by Shock Pressure of Breaking Wave

This paper researches numerically by finite element method about responses of coastal dikes under shock pressure of breaking water waves. It was found that the tension and shear failure developed in the supper part of back-filling soil by shock pressure waves. The generation of the excess pore water pressure causes to scour in the toe and suck out in back-filling soil. Coastal dikes become dangerously when the breaking wave height and the breaking water depth are large. the angle of dike is sleep, the penetration depth is small and the thickness of concrete wall is thin.

Reliability analysis of a coastal dike

A model for probabilistic analysis of the extreme wave run-up on a coastal dike has been defined for evaluation of the event of waves overtopping the dike during severe wave action under a combination of a high tide and a storm surge. The model is applied to an analysis of the reliability of a selected example dike. Uncertainties in various governing environmental and topographic properties are included. The reliability is computed according to a second-order reliability method. A sensitivity study is included.

An Experimental Study of Irregular Wave Forces on a Coastal Dike

ABSTRACTThe force caused by the wave action on a dike is one of the main factors in the design of coastal dikes. In order to make clear the relationship between incident waves in deep water and wave forces on a dike, experimental investigations were carried out in a wave channel equipped with an irregular wave generator. The main interest lies in the effect of wave irregularity.The frequancy distribution of irregular wave forces changes from wide distribution in deep water to narrow one in shallow water. The relationship between the significant wave height and the significant wave force which is defined by the same method as that for the wave height is expressed as P1/3= wH (h+1.25 H1/3). In addition, an approximately constant response is obtained over the frequency range in which the major wave energy is contained. As far as the waves attack a dike in a breaker zone, there is no large difference between irregular and regular waves because of the narrow distribution of wave heights.

An Experimental Study of Irregular Wave Run-Up on a Coastal Dike

ABSTRACTThe force caused by the wave action on a dike is one of the main factors in the design of coastal dikes. In order to make clear the relationship between incident waves in deep water and wave forces on a dike, experimental investigations were carried out in a wave channel equipped with an irregular wave generator. The main interest lies in the effect of wave irregularity.The frequancy distribution of irregular wave forces changes from wide distribution in deep water to narrow one in shallow water. The relationship between the significant wave height and the significant wave force which is defined by the same method as that for the wave height is expressed as P1/3= wH (h+1.25 H1/3). In addition, an approximately constant response is obtained over the frequency range in which the major wave energy is contained. As far as the waves attack a dike in a breaker zone, there is no large difference between irregular and regular waves because of the narrow distribution of wave heights.

WAVE RUN-UP AMD OVBRTOPPINC ON COASTAL DIKES

The experimental results of wave run-up and overtopping on coastal dikes with a steep seaside slope are presented. Wave run-up heights are calculated by regarding to the crest height of standing wave m none breaking zone and to the reflected bore height m breaking zone. The calculated values indicate good agreement with the experimental results. As for wave overtopping, the experimental results are mainly discussed with regard to the effect of wave breaker to overtopping phenomena.