Offshore Breakwater Research Articles

Laboratory investigation on hydraulic performance of enlarged pile head breakwater

Coastal erosion of beaches has been a common problem around the world. One of the eco-friendly control measures for coastal erosion is to dissipate the energy of waves impinging on the shores by constructing offshore breakwater. Pile breakwater is one such type of offshore breakwater that consists of a number of closely spaced piles. Construction of piles at closer spacing is highly challenging and expensive. This problem can be addressed by reducing the number of piles and modifying the pile with an enlarged head in the vicinity of the water surface, where wave energy is concentrated. In the present study, an experimental investigation on the hydraulic performance of enlarged pile head breakwater is conducted in a wave flume. The concept breakwater is subjected to monochromatic waves of varying wave heights, wave periods and water depth. The experimental results show that the least value of transmission coefficient is 0.62 and reflection coefficient is 0.123 with the highest value of dissipation coefficient of 0.77 for the structural configuration of b/D ratio of 0.2, D/Hmax of 0.6 and Y/Hmax of 1.0 at a water depth of 0.3 m. Observed results are encouraging and are in line with the similar type of pile breakwaters in a single row. The present experimental data is also validated with the available theoretical solutions. Since the results from the compared theoretical solution are not in good agreement, a hybrid theoretical model is reconstructed based on experimental results of pile head breakwater. The proposed modified version of the hybrid equation predicts encouragingly better transmission, reflection and dissipation coefficient than the existing solutions. Moreover, the results predicted by the proposed hybrid equation are in good agreement with that of other similar pile breakwater models.

Simulating wave transmission in the lee of a breakwater in spectral models due to overtopping

Spectral wave models have experienced constant development and vast improvements over the past decades. They are constantly being extended and refined in order to cover the complex wave transformation processes that take place in the coastal zone. Nevertheless, wave transmission due to overtopping has not been treated similarly yet. In this paper, a methodology to include wave generation due to overtopping in spectral wave models is presented. Incorporation of overtopping aims at better simulating the wave disturbance in the lee side of a system of offshore breakwaters and the induced hydrodynamic processes. So far, the waves generated due to wave overtopping were being neglected. The methodology consists of executing sequential simulations at small time step intervals and whenever wave overtopping occurs in a breakwater, waves are generated and transmitted in the lee side of the structure. This is achieved by modifying the boundary condition at the lee of a coastal structure to account for wave generation due to overtopping. Additionally, the transmitted spectrum source function was modified, to capture the observed transfer of energy in the higher frequencies of the spectrum due to the aforementioned overtopping process. The above methodology was implemented in the open source wave model TOMAWAC and verification with experimental measurements was carried out yielding satisfactory results. Inclusion of wave transmission due to overtopping in spectral wave models is considered to be a valuable asset, especially for the simulation of inshore hydrodynamic processes.

Stepped Submerged Offshore Breakwaters for Wave Energy Dissipation

Stepped Submerged Offshore Breakwaters for Wave Energy Dissipation

Using Drone and LiDAR to Assess Coastal Erosion and Shoreline Change due to the Construction of Coastal Structures

Tak, W.J.; Jun, K.W., Kin, S.D., and Lee, H.J., 2020. Using drone and LiDAR to assess coastal erosion and shoreline change due to the construction of coastal structures. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 674-678. Coconut Creek (Florida), ISSN 0749-0208.Recently, The construction of structures on the coastal zone near estuaries, which are the supply sources of sediments, causes a variation in the waterway; this induces a change in the surrounding coasts, and the resulting coastal erosion can adversely affect the lives of the local residents. In the case of a balanced sediment flow, the quantity of the sediment deposited on the coast is equal to the quantity of the released sediment. However, an increase in either of the quantities causes an imbalance in the sediment transport; consequently, the sand is either deposited or eroded in the coastal or proximate shore regions. In this study, the changes in the shoreline and Wolcheon Beach region located on the east coast of Korea was monitored between 2010 to 2019 investigate the phenomena of coastal erosion and beach deformation. The shorelines, beach width, and beach profile were primarily monitored by employing a drone and a terrestrial LiDAR. The results showed that the sediments were transported northward in summer and southward in winter until 2010 in Wolcheon Beach; however, this seasonal sediment transport was blocked during 2011–2012 by the construction of coastal structures such as breakwaters, leading to partial coastal erosion and sedimentation. Wolcheon Beach originally had the coastal characteristics of the Korean East Coast region (2010), but the sediment transport changed due to the variations in the waterway by the construction of coastal structures, leading to a significant change in the coast (2011). In addition, the northern beach volume increased with respect to estuary, while the southern beach volume decreased. When the offshore breakwater was constructed, the northward sediment occurred dominantly in the shield area. In particular, the planar layout of the harbor facilities concentrated the waves, which increased the quantity of the northward sediment.

2-D Coastal Hydrodynamic Model to Evaluate the Performance of the Abu Dhabi Shore Protection System

The main shoreline of the Abu Dhabi City Main Island is facing the Arabian (Persian) Gulf from the north-west side and is exposed to continuous current wave action. Therefore, a shore protection system was developed on this side from the Main Island. The shore protection system consists of onshore and offshore breakwaters, huge volumes of damped sand, and an artificial island known as the Lulu Island. In this study, the performance of the current shore protection system of Abu Dhabi City Main Island was evaluated using the Costal Graphical Wave (CGWAVE) 2D-hydrodynamic model. The model can simulate the characteristics of the waves when they approach the breakwaters or the shoreline. Our study has shown that the breakwaters manage to dissipate most of the wave energy before the waves reach the Lulu Island, whereas this island protects the Abu Dhabi City shoreline by creating an elongated sea area between the island and the shoreline that is devoid of any wave action. The constructed shore protection system was also efficient in controlling beach erosion and flooding by damping the wave energy.

An evaluation of a new offshore breakwater at Sattahip Port, Thailand

Careful planning for a port development is vital. Offshore breakwater is known to reduce wave height approaching a port, but it is not always the case. Different ports have different characteristics. This article chose to analyse Sattahip Port. Necessary information, such as annual wave climate, long-term tidal records, and a bathymetric map were collected and synthesized. Numerical simulations were carried out by the MIKE21 PMS software package. The simulation results showed that the existing breakwater at the port could only protect some parts of it. If the whole area of the port were to be sheltered, a new offshore breakwater would have to be installed at a certain location. The existing breakwater could not be extended because it would interfere with the existing navigational channel. A new breakwater at the nearest island was another option, but it was proven by the simulation results that the new breakwater could not reduce the wave height as planned. If the wave simulation had not been undertaken, decision makers might have proceeded in the wrong direction, and millions of dollars would have been wasted.

Evaluation of beach nourishment works on Miyazaki coast in Japan

Miyazaki Coast have been suffering from severe erosion problem due to the shortage of sediment supply from rivers and the change of waves and nearshore currents by the construction of an offshore breakwater at Miyazaki Port. In order to reproduce a wide sandy beach, a beach nourishment project has been done since 2008 in combination with the installation of Sand-Packed containers that were placed in front of dune. A certain volume of nourishment sand has been installed for the sand fill works that cover Sand-Packed containers, and the rest has been dumped off the coast. The purpose of this research is to evaluate the effectiveness of beach nourishment works with using long-term bottom sounding data. This study discussed the effect of the beach nourishment on longshore sandbar evolution. The change of the sand volume in research area was also discussed in this study.

LIVING SHORELINE DESIGN USING NUMERICAL AND PHYSICAL MODELS TO CREATE A PUBLIC PARK IN EUCLID, OHIO

The shoreline of Euclid, Ohio consists of silty-clay cliffs that are naturally eroding into Lake Erie, supplying sediments to the littoral system. Updrift stabilization and entrapment of sands along the shoreline have led to accelerated deterioration of Euclid’s cliffs along a thousand meter stretch of lakefront. Due to the cliffs’ unstable nature and privately held ownership, long stretches of shoreline are inaccessible and only a few property-owning residents have visual access to the lake. Through state funding and creative negotiations, the City of Euclid and SmithGroupJJR were given permission to create a recreational waterfront park using both hard and soft engineering techniques designed to dynamically adapt to the forces of Lake Erie and not impede natural littoral transport. A series of numerical and physical modeling studies were undertaken to optimize a natural design that will remain stable throughout extreme events. This design married revetments, headland habitat beaches, offshore breakwaters, vertical structures, submerged structures, tee-groin breakwaters, recreational sand beaches, and natural plant stabilization techniques to achieve a stable, resilient waterfront park that can be enjoyed by the public.

REASON OF FIXATION OF MOUTH OF A SMALL RIVER BEHIND NATURAL REEF

The mechanism by which the mouth of a small river is stably fixed in the wave-shelter zone behind an offshore reef composed of natural rocks was studied, taking a small river flowing into the Moriya coast together with two other small rivers as examples. The beach topography around the river mouth and the shape of the stream behind the reef were measured on this coast, and the wave height distribution around the reef was calculated using the angular spreading method, and the reason why the river mouth is stably fixed at this location was considered. Furthermore, the numerical simulation of beach changes using the BG model when an offshore breakwater was installed as a model of a natural reef was carried out to study the longshore change in the berm height. The primary cause for the fixation of a river mouth behind a reef was found to be the decrease in wave height behind the reef, which in turn decreases in the berm height.

LIVING BREAKWATERS: DESIGNING FOR RESILIENCY

In the aftermath of Hurricane Sandy, the Rebuild by Design competition was born to encourage cross-disciplinary collaboration and resilience planning in coastal and flood protection design. The Living Breakwaters project is a layered resilience approach to promote risk reduction, enhance ecosystems, and foster social resilience. Following the competition, the project was awarded $60 million by HUD (US Department of Housing and Urban Development) in June 2013. It is currently in final design and permitting with construction anticipated to begin the summer of 2019. The Living Breakwaters Project is a unique design of an offshore breakwater system to promote coastal resilience in Tottenville, Staten Island, New York. It combines physical risk reduction through wave attenuation and erosion prevention functions with ecological enhancement and habitat creation as an integrated part of the design. This paper explores the modeling and design of these unique coastal engineering and ecological structures.

Wind and wave climate in the vicinity of Bozcaada

One of the most important subjects of coastal engineering is determining the effect of waves on coastal areas. There are different types of marine structures constructed for different purposes such as berths and breakwaters for ports, seawalls for coastal protection, offshore breakwaters and groins.   The basic design tools in planning and designing coastal structures and determining the shoreline changing are wave parameters.Wind and wave climate studies were carried out in Bozcaada coastal region. The wind data used in the wave prediction is obtained from the General Directorate of State Meteorology Affairs. The data includes the hourly wind data for the 30-year period covering the period January 1980-July 2010 for Station number 17111. By evaluating the data, hourly wind distribution percentages, frequency distributions considering direction of wind speeds and direction weighted speed averages were obtained between the years 1980 and 2010. Wave parameters belonging to this region are determined by SMB method which is one of empirical wave estimation methodsWind and wave roses were obtained by using numerical model Mike 21 SW in the thesis comprehensiveness. Wind data required for this model is obtained from ECMWF (European Centre Medium-Range Weather Forecasts) ERA Interim data set. For the calibration of wind – wave models, data is used which was recorded for Bozcaada buoy stations under NATO TU- WAVES project at the coast of Turkey between 21 November 1994- 30 September 1995. When examining the results received from model according to ECMWF data, it has been observed that waves are usually more effective at Bozcaada  in south and  south east direction.

Nocturnal activity and feeding of juvenile channel catfish, Ictalurus punctatus, around offshore breakwaters in Lake Kasumigaura, Japan

Diel changes in occurrence and feeding habits of juvenile channel catfish (Ictalurus punctatus) were examined in offshore breakwater areas in Lake Kasumigaura, Japan, to understand their nocturnal behavioral ecology within a lentic habitat. Juveniles (20–56 mm in standard length) occurred more abundantly in evening and nighttime than in daytime and fed mainly during darkness hours. Major food items comprised chironomid larvae and cladocerans. The relative proportion of those items in stomach contents changed from daytime to evening and nighttime, possibly being partly related to diel changes in prey accessibility.

Multiscale coupled three-dimensional model analysis of the tsunami flow characteristics around the Kamaishi Bay offshore breakwater and comparisons to a shallow water model

ABSTRACTA two-way coupled two-dimensional (2DH) shallow water to three-dimensional (3D) Navier–Stokes equation model, named 2-way Coupled Long Wave to Navier–Stokes 3D (2CLOWNS-3D), is applied to the 2011 Tohoku-oki Earthquake Tsunami in Kamaishi Bay, Japan. 2CLOWNS-3D simulates the entire evolution of the tsunami from its source to inundation at the coast, in which the 3D model component is used to model the flow through the submerged opening of a large-scale offshore tsunami breakwater. 2CLOWNS-3D is compared with a 2DH model simulation in order to identify where it becomes beneficial. It is found that flow rates through the submerged breakwater opening, and thus the resulting inundation heights, are similar between 2DH and 2CLOWNS-3D model simulations when an appropriate momentum dispersion coefficient is applied to the former. However, significant differences between the model simulations are identified in relation to; hydrodynamic forces acting on the submerged caissons, velocities in the large-scale jet structure emanating from the breakwater, and bed shear stresses in the vicinity of the breakwater. Furthermore, the characteristics of the large-scale jet structure simulated by the 3D model are reasonable when employing the realizable k-ε turbulence closure. Our results demonstrate the practical merit of 2CLOWNS-3D for simulating complex geophysical scale flows.

Sustainable coastal zone planning based on historical coastline changes: A model from case study in Tainan, Taiwan

Coastal regions are threatened by natural processes, such as erosion driven by storm surge and the effect of jetties, as well as by human behavior. This study outlines a management framework based on an analysis of a case study dataset of long-term coastal change in southwestern Taiwan. Specifically, the coastal structure of Taiwan’s largest lagoon, Cigu, was analyzed over a 300-year-long period. A series of satellite-derived images between 1974 and 2015 were assessed. The dataset was integrated with a geographic information system (GIS). The results revealed that human activities, including the construction of hard structures along the coastline and along an upstream reservoir, altered the balance of sediment transmission and resulted in the retreat and erosion of barrier sandbars along the coast. A lagoon evolution model revealed that the Cigu Lagoon may disappear in the future. Furthermore, the coastline will continue to retreat because harbor dykes and offshore breakwaters stop sediment transportation to the downdrift. Soft erosion mitigation is suggested as an immediate approach. However, recovering the sediment budget from reservoirs and dykes could be a long-term solution. In principle, the best coastal environmental protection plan from the national involves delaying urbanization and preserving unexploited coastal wetlands.

Reshaping beach morphology by modifying offshore breakwaters

Use of static shore protection structures is often considered an irreversible change toward a decrease in shoreline dynamism, but structures can be modified to make them more compatible with human needs and create a more mobile beach. This concept is documented by comparing changes in shape and volume of the beach and nearshore resulting from modification of emerged, segmented offshore breakwaters to a continuous submerged structure. Emerged, segmented breakwaters were constructed between 1983 and 1987 in Follonica Bay on the Tuscan coast of Italy. The breakwaters created an asymmetric shoreline with beach salients landward of the structures and bays landward of the gaps. Between 2011 and 2013, the breakwaters were removed and the boulders were used to create a continuous submerged breakwater farther offshore, with a wider crest at −0.5 m below mean sea level. The purpose was to achieve better views of the sea and a more equitable beach width alongshore. In the process, natural processes were allowed greater freedom to reshape the beach. The shoreline straightened after alteration, but retreated an average of 12.9 m between 2013 and 2016. This study provides one of the few prototype before-after evaluations of modifying breakwaters to make shorelines function more naturally. The results indicate how human-induced geomorphic changes can occur at the local scale (tens to hundreds of meters alongshore) in response to the perceived needs of local managers, even where the new condition runs counter to the traditional goal of creating a more stable beach for shore protection.

Coastal erosion and accretion in Kuwait – Problems and management strategies

Kuwait is a coastal country with 496 km coast. It is located in the Arabian Peninsula, at the north-western part of Arabian Gulf. Many coastal infrastructures are close to high water line and hence attract erosion, especially in the south. The northern part is significantly dominated by sedimentation. Remote sensing is used to identify the hot spot of erosion and accretion. Kuwait does not have good quality natural stones and needs to be imported from other countries for any coastal structure project and is expensive. Hence innovative coastal protection solutions, which are cost competitive, environment friendly, easy to fabricate, install and reorient, are needed. Geo-bags, filled with sand are field tested. New type of floating breakwaters are developed which has reduced width compared to conventional pontoon breakwaters, by introducing skirt walls at the keel of the floating breakwater. It is found that material saving of more than 60%–75% is possible when compared to rubble mound offshore breakwaters. Many coastal infrastructures in the northern part of Kuwait are suffering due to sedimentation. Detailed field, lab and numerical modeling studies were carried out to understand the sedimentation problem and for providing solutions to reduce the degree of accretion in the marinas and seawater intake structures. Work is in progress for rolling out the Integrated Coastal Zone Management Plan for Kuwait.

Laboratory experiments on beach change due to nearshore mound placement

Movable-bed large-scale laboratory experiments were conducted to examine the fate and quantify the benefits of nearshore placed dredged material. Two tests were performed on a beach classified as eroding [19] for mounds placed in the active zone described by Hands and Allison [12] at two depths. Mound sand was dyed to provide contrast and to differentiate it from the native sand beach. Beach surveys were performed intermittently during each experiment with a laser scanner. In addition to beach change elevations, the scanner provided RGB color components, which permitted tracking of the mound sand. The experiments showed that the mound sand dispersed rapidly and was transported mainly downdrift. Sand accumulation was observed on the beach onshore and adjacent to the mounds mainly due to wave sheltering of the mounds described as the longshore effect by [28]. There was little contribution to onshore accretion from cross-shore migration of the mounds. Beach response was similar to that of an offshore breakwater in which the mounds provided a wave shadow zone to the leeward beach. The results from the experiment will provide validation data for the numerical morphological model C2SHORE [15].

The Effects of Selected Types of Active Bank Stabilization

A major issue related to the banks of reservoirs is their gradual erosion caused by waves - those incurred by the wind, the movement of vessels, or otherwise. A possible way of the bank protection is the implementation of an active bank stabilization. Offshore breakwaters are designed for the cases where the shore itself is protected for some reason (e.g., protection of nesting birds, etc.) and a direct intervention in the bank is not possible. This is the situation of heavily disturbed banks of Brno reservoir, where the experiment described has been conducted and the results are presented in this paper.

Subsidence estimation of breakwater built on loosely deposited sandy seabed foundation: Elastic model or elasto-plastic model

In offshore area, newly deposited Quaternary loose seabed soils are widely distributed. There are a great number of offshore structures has been built on them in the past, or will be built on them in the future due to the fact that there would be no very dense seabed soil foundation could be chosen at planed sites sometimes. However, loosely deposited seabed foundation would bring great risk to the service ability of offshore structures after construction. Currently, the understanding on wave-induced liquefaction mechanism in loose seabed foundation has been greatly improved; however, the recognition on the consolidation characteristics and settlement estimation of loose seabed foundation under offshore structures is still limited. In this study, taking a semi-coupled numerical model FSSI-CAS 2D as the tool, the consolidation and settlement of loosely deposited sandy seabed foundation under an offshore breakwater is investigated. The advanced soil constitutive model Pastor-Zienkiewics Mark III (PZIII) is used to describe the quasi-static behavior of loose sandy seabed soil. The computational results show that PZIII model is capable of being used for settlement estimation problem of loosely deposited sandy seabed foundation. For loose sandy seabed foundation, elastic deformation is the dominant component in consolidation process. It is suggested that general elastic model is acceptable for subsidence estimation of offshore structures on loose seabed foundation; however, Young's modulus E must be dependent on the confining effective stress, rather than a constant in computation.

The Characteristics of Sea Water Quality Change of Fishing Port in East Coast of Korea Using GIS

In an attempt to understand changes in sea environment owing to constructing fishing port in the Eastern Sea ports, by comparing the data from Environmental Impact Assessment (EIA) on 2006 and those obtained from post-Environmental Impact Assessment (post-EIA), the impact of the construction on the sea environment, and the temporal and spatial distributions of sea environmental parameters were analyzed. After analyses, it could be found that the values were increased in all the items except pH, influencing nutritional salts (T-N, T-P) and SS mostly with the severest degrees. Although the heavy metals except Hg were detected since construction, the values were lower than the standard ones stipulated in the environmental standards in areas of the sea (standards for short periods in the light of protecting sea environment). Furthermore, the fact that heavy metals were detected after beginning offshore breakwater construction, although the heavy metal concentrations were lower than the criteria from sea water environmental standard, means that the port facility construction influence the concentration of heavy metals in the seawater.