Showing papers on "Breakwater published in 2021"

Coastal Structures as Beach Erosion Control and Sea Level Rise Adaptation in Malaysia: A Review

Abstract: The shoreline of Malaysia is exposed to threats of coastal erosion and a rise of sea level. The National Coastal Erosion Study, 2015 reported that 15% of an 8840 km shoreline is currently eroding, where one-third of those falls under the critical and significant categories that require structural protection. The Study of Sea Level Rise in Malaysia, 2017 presented a sea-level increase of 0.67–0.74 mm on average yearly. This study reviewed selected coastal protection structures along the shoreline of Malaysia as an erosion control and sea-level rise adaptation based on coastal management strategies. Hard structures such as rock revetment and breakwater are commonly used as erosion protection systems in the “hold the line” strategy. Increased platform level of seawalls and earth bunds, considered as an “adaptation” approach, are effective in erosion protection and are adaptive to sea-level rise. Mangrove replanting is suitable as a “limited intervention” approach in minimizing the long-term impact of both threats. However, offshore breakwater, groyne, and geotextile tubes are solely for protection purposes and are not as effective for sea-level rise adaptation. As the sea level is continuously increasing, their function as coastal protection will also become less effective. In summary, this comprehensive review on coastal protection in Malaysia will benefit the related agencies on the future assessment.

Physical modeling of the dynamics of a revetment breakwater built on reclaimed coral calcareous sand foundation in the South China Sea—tsunami wave

Abstract: In this study, taking the reclamation engineering in the South China Sea as the background, several wave flume experiments (geometrical similarity scale is set as 1:10) are performed to study the dynamics and the stability of a reclaimed calcareous sand foundation and the breakwater built on it, under the impacting of tsunami wave. Tsunami wave is similarly simulated by N wave in the wave flume. It is shown by the experimental results that the revetment breakwater has no visible displacement, and there is no significant deformation in the reclaimed coral sand foundation, regardless the foundation is in dense or loose state under tsunami wave attacking. Furthermore, there is indeed excess pore pressure generated in the reclaimed coral foundation with a maximum magnitude of 1.5 kPa, caused by the water overtopping or the seepage. It is found that the excess pore pressure has not caused liquefaction in the reclaimed calcareous sand foundation due to the fact that there is only one peak impacting for the tsunami wave-induced load, rather than a cyclic one. Finally, it is concluded that the reclaimed calcareous sand foundation and the breakwater built on it are basically stable under tsunami wave impacting. However, the excessive water overtopping would be a potential threat for the vegetation behind the breakwater, as well as for the underground desalinated water in the reclaimed lands.

Morphodynamic Evolution of a Nourished Beach with Artificial Sandbars: Field Observations and Numerical Modeling

Abstract: Beach nourishment, a common practice to replenish an eroded beach face with filling sand, has become increasingly popular as an environmentally friendly soft engineering measure to tackle coastal erosion. In this study, three 200 m long offshore submerged sandbars were placed about 200 m from the shore in August 2017 for both coastal protection and beach nourishment at Shanhai Pass, Bohai Sea, northeastern China. A series of 21 beach profiles were collected from August 2017 to July 2018 to monitor the morphological changes of the nourished beach. Field observations of wave and tide levels were conducted for one year and tidal current for 25 h, respectively. To investigate the spatial-temporal responses of hydrodynamics, sediment transport, and morphology to the presence of three artificial submerged sandbars, a two-dimensional depth-averaged (2DH) multi-fraction sediment transport and morphological model were coupled with wave and current model and implemented over a spatially varying nested grid. The model results compare well with the field observations of hydrodynamics and morphological changes. The tidal range was around 1.0 m and the waves predominately came from the south-south-east (SSE) direction in the study area. The observed and predicted beach profiles indicate that the sandbars moved onshore and the morphology experienced drastic changes immediately after the introduction of sandbars and reached an equilibrium state in about one year. The morphological change was mainly driven by waves. Under the influences of the prevailing waves and the longshore drift toward the northeast, the coastline on the leeside of the sandbars advanced seaward by 35 m maximally while the rest adjacent coastline retreated severely by 44 m maximally within August 2017–July 2018. The model results demonstrate that the three sandbars have little effect on the tidal current but attenuate the incoming wave significantly. As a result, the medium-coarse sand of sandbars is transported onshore and the background silt is mainly transported offshore and partly in the longshore direction toward the northeast. The 2- and 5-year model simulation results further indicate that shoreline salient may form behind the sandbars and protrude offshore enough to reach the sandbars, similar to the tombolo behind the breakwater.

Numerical investigation on the hydrodynamic performance of a new designed breakwater using smoothed particle hydrodynamic method

Abstract: Floating breakwaters have better performance than fixed breakwaters in deep water conditions owing to their higher durability and lower cost. To evaluate the hydrodynamics of a floating breakwater system, a coupling model between smoothed particle hydrodynamics and a multisegmented quasi-Static method is developed. The free-floating and the moored cases are firstly employed as benchmarks to validate the accuracy and stability of the proposed numerical procedure. The coupling model is then utilized to investigate the wave-attenuating performance of a novel configuration of floating breakwater under different environmental conditions. It is demonstrated that the induced response and the tension characteristics are both in good agreement with experimental results, which means that the developed coupling model is capable of predicting the hydrodynamics of the floating breakwater system. Moreover, it is also suggested that the newly-proposed configuration shows more satisfactory wave-attenuating performance than the classical type by inducing more complex velocity fields surrounding the breakwater.

Evaluating essential processes and forecast requirements for meteotsunami-induced coastal flooding

Abstract: Meteotsunamis pose a unique threat to coastal communities and often lead to damage of coastal infrastructure, deluge of nearby property, and loss of life and injury. The Great Lakes are a known hot-spot of meteotsunami activity and serve as an important region for investigation of essential hydrodynamic processes and model forecast requirements in meteotsunami-induced coastal flooding. For this work, we developed an advanced hydrodynamic model and evaluate key model attributes and dynamic processes, including: (1) coastal model grid resolution and wetting and drying process in low-lying zones, (2) coastal infrastructure, including breakwaters and associated submerging and overtopping processes, (3) annual/seasonal (ambient) water level change, and (4) wind wave-current coupling. Numerical experiments are designed to evaluate the importance of these attributes to meteotsunami modeling, including a “representative storm” scenario in the context of regional climate change in which a meteotsunami wave is generated under high ambient lake-level conditions with a preferable wind direction and speed for wind-wave growth. Results demonstrate that accurate representation of coastal topography and fully resolving associated hydrodynamic processes are critical to forecasting the realistic hazards associated with meteotsunami events. As most of existing coastal forecast systems generally do not resolve many of these features due to insufficient model grid resolution or lack of essential model attributes, this work shows that calibrating or assessing existing forecast models against coastal water level gauges alone may result in underestimating the meteotsunami hazard, particularly when gauging stations are sparse and located behind harbor breakwaters or inside estuaries, which represent dampened or otherwise unrepresentative pictures of meteotsunami intensity. This work is the first hydrodynamic modeling of meteotsunami-induced coastal flooding for the Great Lakes, and serves as a template to guide where resources may be most beneficial in forecast system development and implementation.

Hydrodynamic performance of tire-based floating breakwater

Abstract: The hydrodynamic characteristics (wave transmission, reflection, and dissipation) of nine different scrap-tire floating breakwater configurations are studied in a wave flume for a wide range of inp...

Hydraulic and structural assessment of a rubble-mound breakwater with a Hybrid Wave Energy Converter

Abstract: Seaports’ breakwaters serve as important infrastructures capable of sheltering ships, facilities, and harbour personnel from severe wave climate. Given their exposure to ocean waves and port authorities’ increasing awareness towards sustainability, it is important to develop and assess wave energy conversion technologies suitable of being integrated into seaport breakwaters. To fulfil this goal whilst ensuring adequate sheltering conditions, this paper describes the performance and stability analysis of the armour layer and toe berm of a 1/50 geometric scale model of the north breakwater extension project, intended for the Port of Leixoes, with an integrated hybrid wave energy converter. This novel hybrid concept combines an oscillating water column and an overtopping device. The breakwater was also studied without the hybrid wave energy device as to enable a thorough comparison between both solutions regarding structural stability, safety, and overtopping performance. The results point towards a considerable reduction in the overtopping volumes through the integration of the hybrid technology by an average value of 50%, while the stability analysis suggests that the toe berm of the breakwater is not significantly affected by the hybrid device, leading to acceptable safety levels. Even so, some block displacements were observed, and the attained stability numbers were slightly above the recommended thresholds from the literature. It is also shown that traditional damage assessment parameters should be applied with care when non-conventional structures are analysed, such as rubble-mound breakwaters with integrated wave energy converters.

Assessment of dynamic pressure and wave forces on vertical-caisson type breakwater

Abstract: The design and construction of coastal structures such as breakwaters, at great water depths is rapidly increasing as a result of the increasing draught of large vessels and off-shore land reclamat...