Types Of Seawalls Research Articles

Numerical modelling of mangrove merged with seawall for investigating wave mitigation over flat topography

In this study, numerical modelling to see the effect of mangrove merged with seawall on wave mitigation over flat topography is developed. The model is based on Navier-Stokes equations. Resistance of the mangrove is described using Manning friction, whereas the seawall is created from particles and added directly to the topography. Numerical solution of the model is solved using Smoothed Particle Hydrodynamics (SPH). Two types of seawalls; vertical and incline seawall are used. Results of the numerical simulations show that existence of the mangrove merged with vertical seawall can reduce 10.52191% in wave height and prevent the wave to pass the seawall. Whereas the existence of the mangrove merged with incline seawall can reduce 15.39512% in wave height but the wave still passes the seawall.

Experimental investigating on the reflected waves from the caisson-type vertical porous seawalls

The hydrodynamic efficiencies of caisson-type vertical porous seawalls used for protecting coastal areas were calculated in this study. Physical models were developed to compare the wave reflection from vertical plane, semi-porous, and porous seawalls caused by both regular and random waves. Tests were carried out for a wide range of wave heights, wave periods, and different water depths (d=0.165, 0.270 and 0.375 m). The performance regarding the reflected waves from porous and semi-porous seawalls showed improvement when compared with those from the plane seawall. The reflection coefficients of the porous and semi-porous seawalls were calculated as 0.6 and 0.75, respectively, while the coefficient for the fully reflecting plane vertical wall was significantly higher (0.9). It was also observed that the reflection coefficient decreases with increase in wave steepness and relative water depth. In addition, the reduction in the reflection coefficient of porous and semi-porous seawalls, as compared to that of a plane seawall, was observed for both regular and random waves. New equations were also proposed to calculate the reflection coefficient of different types of seawalls with the aid of laboratory experiments. By verifying the developed equations using some other experimental data, it was validated that the equations could be used for practical situations. The results of the present study can be applied to optimize the design of vertical seawalls and for coastal protecting schemes.

Experimental study on tsunami risk reduction on coastal building fronted by sea wall.

This experimental study was conducted to idealize the efficacy of sea wall in controlling the tsunami forces on onshore structures. Different types of sea walls were placed in front of the building model. The tsunami forces and the wave heights were measured with and without the sea wall conditions. Types of sea wall, wall height, and wall positions were varied simultaneously to quantify the force reductions. Maximum of 41% forces was reduced by higher sea wall, positioned closer proximity to the model whereas this reduction was about 27% when the wall height was half of the high wall. Experimental investigations revealed that wall with adequate height and placed closer to the structures enables a satisfactory predictor of the force reduction on onshore structures. Another set of tests were performed with perforated wall placing near the building model. Less construction cost makes the provision of perforated sea wall interesting. The overall results showed that the efficacy of perforated wall is almost similar to solid wall. Hence, it can be efficiently used instead of solid wall. Moreover, overtopped water that is stuck behind the wall is readily gone back to the sea through perforations releasing additional forces on the nearby structures.

Numerical Simulation of Wave Overtopping Based on DualSPHysics

To obtain a more detailed description of wave overtopping, a 2-D numerical wave tank is presented based on an open-source SPH platform named DualSPHysics, using a source generation and absorption technology suited for SPH methods with analytical relaxation approach. Numerical simulation of regular wave run-up and overtopping on typical sloping dikes is carried out and satisfactory agreements are shown between numerical results and experimental data. Another overtopping simulation of regular wave is conducted against six different types of seawalls (vertical wall, curved wall, recurved wall, 1:3 slope with smooth face, 1:1.5 slope with smooth face and 1:1.5 slope with stepped-face), which represents the details of various breaking waves interacting with different seawalls, and the average deviation of wave overtopping rate is 6.8%.

TSUNAMI DAMAGES OF NAKOSO COAST DUE TO THE 2011 TOHOKU TSUNAMI

A post-2011 Tohoku earthquake tsunami survey was conducted at the Nakoso Coast, Fukushima Prefecture, Japan, on Mar 24-25 and Apr 1-2, 2011. Spatial distribution of the tsunami inundation height, together with the seawall height and damages, was investigated. We found a sharp contrast of tsunami damages within the target area; tsunami damage is the most serious in the north region (north of the Samegawa River) where seawalls with different heights played diverse roles for protection of local community. A relatively high seawall in this region kept intact after tsunami attack, and protected the lee side human properties; whereas, 71% of the low seawalls were broken during the tsunami and the disaster developed in the corresponding sheltered area. A sharp contrast at the boundary of these two types of seawalls was observed. Behind the high seawall, the tsunami intensity and velocity were significantly reduced and the inundation depth is only 0.6 m. Nevertheless, tsunami intensity was enhanced in the seawall-broken area with an inland inundation depth being 4.7 m, which ruins away the local houses. In the middle region between the Samegawa River and the Bindagawa River, the high seawall survived from the tsunami attack. We confirmed that the coastal pine tree forest, serving as a buffer zone, played a significant role in reducing the tsunami height approximately by 4 m within a cross-shore distance of 230 m. To the south of the Bindagawa River, the tsunami damage is the mildest due to the protection by the robust high seawall as well as high elevation of land topography.

Flexible Seawalls: Modified Bulkhead Approach

AbstractSeawalls played an important role in protecting harbors and multiple beach properties along the country’s East and West Coasts, coast line of the Gulf of Mexico, and the Great Lakes. Engineers successfully used different types of seawalls, ranging from simple gravity walls to flexible sheet pile walls. Until recently industry interchangeably used the term bulkhead or seawall. The majority of bulkheads can be built as simple flexible sheet pile soil retaining structures, whereas seawalls have to be designed for an additional set of loads that includes large hydrodynamic forces. The difference between two structures becomes apparent in toll seawalls designed for large magnitude wave-generated pressures produced by storm or seismic events. The “Great Storm” that pounded the West Coast in January 1988, was one such events. Significant wave height (Hs) along the beach during that event was recorded to be in excess of 16 ft. Waves of such magnitude may carry high energies that can be destructive to the ...

波力発電と反射波の低減を目的とする遊水室型護岸の開発について

A new reflection wave dissipater that has also a wave energy extraction function for the electric power generation has been developed. In order to expand the effective range of wave frequency, a double-water-chamber type of seawall was newly proposed. The wave energy extraction devices presumed in this study are air and water turbines. The oscillating water column type of wave power extraction was assumed. Typically, by mounting a horizontally rolling turbine near the opening of the water chamber, the kinematic energy of wave induced jet flows from the opening can be extracted. The basic characteristic of a double-water-chamber type of seawall has been extensively examined from both the theoretical and experimental points of view.

Hydrodynamic Characteristics of Curved-Front Seawall Models Compared with Vertical Seawall under Regular Waves

Abstract Seawalls remain one of the most widely adopted coastal-protection measure. The seawalls should be stable to ensure safety and optimally use the coastal space with a minimum or no waves overtopping but still keeping the crest elevation low. This may possibly be achieved by reshaping the front of the structure in such a way that it offers maximum resistance to the flow or enhances the dissipation of incident wave energy. With this as the background, an experimental study measuring run-up and overtopping of three different types of curved-front face seawall models, as well as the dynamic pressures exerted on each of them, was carried out. The measured parameters for the three types of seawalls are compared with that for a vertical seawall. All the tests were carried out with the models rigidly fixed over a bed slope of 1 in 30 in a wave flume and subjected to the action of regular waves. The details of the test facility, models, experimental program, results, and analysis are presented and discussed...

Characteristics of Wave Overtopping on Vertical Type Seawall Covered with Wave-dissipating Blocks

In recent years, seawalls coated with wave-dissipating blocks heve been set in front of upright seawalls. However, wave overtopping on this type of seawall is not fully investigated. Therefore, in this paper, characteristics of wave overtopping on upright seawall covered with wave-dissipating blocks was examined experimentally. From the results, it is found that this type of seawall is effective to reduce the wave overtopping rate. The crest height of the seawall is less than the height in upright seawall case to get the same wave overtopping rate. In addition, an easy method to estimate the runup height on the seawall has been suggested.

Mitigation of Wave Overtopping Rate in Offshore Airport by Permeable Bed Type Seawall

Large wave overtopping due to storms sometimes causes heavy inundation damage in an offshore airport surrounded with the sea. The wave overtopping rate at seawall lines is significantly changed by the local sea bed topography and the type of seawall. In this paper the variation of wave overtopping rate along the seawall line including a corner part is studied in an experimental basin with a directional wave maker. In the later part of the paper, the countermeasures to reduce wave overtopping at the seawall are discussed. A seawall attached with a wave absorbing permeable bed behind it is proposed for the airport seawall and is investigated experimentally. Experimental results demonstrate the wave overtopping rate becomes remarkably small for the new type seawall.

HYDRAULIC MODEL TEST ON WAVE OVERTOPPING FOR COMPOSITE-TYPE SEAWALLS WITH LOW CROWN HEIGHT

Offshore man-made islands and reclaimed lands are planned for making use of ocean space. Seawalls are important to reduce wave overtopping rate. Recently, seawalls with low crown height are needed to reduce construction cost. Hydraulic model tests were conducted to evaluate overtopping quantity of four kinds of composite-type seawalls with low crown height. Firstly, wave overtopping quantity is measured to determine the crown heights. Secondly, wave pressure on caissons and parapet is measured to design four types of seawalls considering the site condition. At last, volume of wave dissipating concrete block and concrete caisson is compared with each other in order to evaluate cost reduction of seawall construction. It was found out that the seawall with concrete block on the top of caisson has the highest performance on reduce wave overtopping.

OPTIMUM DESIGN OF EMBEDDED STEEL PLATE CELLULAR BULKHEADS

The embedded steel plate cellular bulkhead has been developed as a new type of sea wall which is applicable even for poor sea beds and deep water sites. As the sea wall is a widely extended and huge structure, economical construction is needed. In this study, the optimization technique was applied for the minimization of the total construction cost of the embedded steel plate cellular bulkheads including the ground improvement cost. This technique was applied also for the clarification of the relationship between the design factors and the constraints. Through the numerical computation, the optimum cross sections of the embedded steel plate cellular bulkhead and the optimum area of ground improvement were obtainedd and the useful informations for the optimum design of this structure were provided.

SEAWALLS IN DEEP SEAS

Features in wave overtopping of two new types of seawalls designed to be built in considerably deep sea conditions are presented herein. One of those is the seawall of concrete caisson with a parapet wall and armor blocks on the top of the caisson, and another one is the seawall with a slitted box-type wave absorber. The former type of seawall has successfully been constructed in the Japan Sea and the Seto Inland Sea and is also to be constructed at a site directly exposed to an open sea of the Pacific Ocean in 1980 and 1981. The latter type of seawall was proposed in 1977 after numerous experiments and has been under construction in the Port of Osaka since 1978. The results of the experiments on the wave overtopping over the slit-type seawall were compared with the calculated results, obtained by an analysis in which the wave overtopping over a parapet wall was considered similar to the phenomenon of flow over sharp-edged weirs having time-dependent overflow-head. The calculated curves obtained are in good agreement with the experimental results. The designs of these two types of seawall are also presented herein.

DESIGN AND PERFORMANCE OF SEA WALLS IN MISSISSIPPI SOUND

The purpose of this paper is to describe briefly the various types of sea walls that have been constructed on Mississippi Sound, the performance of each type, and the conclusions with regard to sea wall design that can be drawn from this information.