Reduce Wave Energy Research Articles

EFEK MANGROVE TERHADAP PEREDAMAN ENERGI GELOMBANG

The research was conducted in Malalanda Village and Linsowu Village, North Buton Regency in November 2021 by collecting primary data (interviews and direct measurements in the field) and processing secondary data to determine the role of mangroves in reducing wave energy based on mangrove conditions (density, thickness and diameter of mangrove trunks). ) using the Thaha Method (2001). Wave conditions in the Kulisusu Bay area are predicted using wind data from the Beto Ambari Bau-Bau BMKG Station followed by predictions of the height and depth of the breaking waves. Changes in shoreline at two research stations that have different coastal protection (dykes and mangrove forests) were analyzed using ArcGIS 10.3 software and then expressed changes in shoreline in quantitative units. Based on the results of the analysis, it was found that the maximum wave height in the study area ranged from 2.27 m – 3.9 m with a maximum breaking wave height of 2.50 m and 3.57 m at a depth of 1.07 m – 3.15 m at a distance of 100 m to 200 m. The change in shoreline is greater at station 2, which is 6.48 m, and the condition of the mangrove forest at the research station has a thickness of 65.61 m and a porosity of 0.72 capable of damping waves with values ranging from 26.424% - 99.98%.Keywords: wave, mangrove, wave attenuation

Sustainability & Comparative Impact Analysis of Coral Reef Bleaching in Indian Context

An estimated value of 500 million of the population are directly benefited through coral reefs related jobs, food and defence of coastal areas. Coral reefs help to reduce wave energy by 97%. They help to protect the coastal areas from storms, floods and wave energy by 97%. Natural disasters such as Tsunami and erosion of coastal areas are protected by reefs. In this process, they help to protect the lives of many staying in the coastal areas including animals, properties, and other natural resources. There are reasons for reef deterioration like change of climate, high pollution, destructive fishing, bleaching of coral reefs is a big concern now worldwide. Severe coral bleaching is also reported in India. A significant rise in the surface temperature of Sea has become a critical reason for coral bleaching. This work attempts to Study the link between sustainability , SDG goals of 2030 given by United Nations and coral bleaching. In this work study period is focused from 1985 to 2021 in the Indian coral reef bleaching areas.

Wave attenuation prediction of artificial coral reef using machine-learning integrated with hydraulic experiment

Various prevention methods have been proposed to resolve such coastal erosion problems, known as an important social issue in many countries. However, most of the methods designed and constructed involve gravity-type structures, causing various problems such as the obstruction of seawater circulation and changes in water quality and marine ecosystem. In this study, we propose an eco-friendly artificial coral reef structure that can control coastal erosion and help preserve the coastal environment. We investigated the wave height distribution and energy reduction characteristics through a two-dimensional hydraulic model experiment under various conditions, including different external force conditions (wave height, water depth, and wave period) and design conditions (dimensionless crown width and submergence ratio). Furthermore, we investigated the drift sand control and morphological characteristics of artificial coral reefs through a movable bed experiment. The results of the hydraulic experiment revealed that the dimensionless crown width and submergence ratio factors had a dominant effect on the wave height attenuation. In addition, the artificial coral reef structures outperformed broadly applied tetrapod structures in terms of coastline advancement and seabed protection under storm wave conditions. Moreover, to estimate the wave attenuation characteristics of artificial coral reefs, we introduced a prediction study of wave attenuation characteristics of artificial coral reefs to propose an explicit method composed of weights and biases using modified artificial neural network. We found that the method of calculating the wave dissipation coefficient calculated with the presented weight and bias matrix shows more accurate reliability than the calculation method based on the existing empirical formula.

How Much Marsh Restoration Is Enough to Deliver Wave Attenuation Coastal Protection Benefits?

As coastal communities grow more vulnerable to sea-level rise and increased storminess, communities have turned to nature-based solutions to bolster coastal resilience and protection. Marshes have significant wave attenuation properties and can play an important role in coastal protection for many communities. Many restoration projects seek to maximize this ecosystem service but how much marsh restoration is enough to deliver measurable coastal protection benefits is still unknown. This question is critical to guiding assessments of cost effectiveness and for funding, implementation, and optimizing of marsh restoration for risk reduction projects. This study uses SWAN model simulations to determine empirical relationships between wave attenuation and marsh vegetation. The model runs consider several different common marsh morphologies (including systems with channels, ponds, and fringing mudflats), vegetation placement, and simulated storm intensity. Up to a 95% reduction in wave energy is seen at as low as 50% vegetation cover. Although these empirical relationships between vegetative cover and wave attenuation provide essential insight for marsh restoration, it is also important to factor in lifespan estimates of restored marshes when making overall restoration decisions. The results of this study are important for coastal practitioners and managers seeking performance goals and metrics for marsh restoration, enhancement, and creation.

Estimation of surface wave induced fluid mud thickness on the seafloor

Mud-induced dissipation of surface wave energy is a key mechanism that affects wave propagation in muddy environments. The properties of fluid mud on seafloors required to simulate wave dissipation over shallow waters are often unknown in investigations where wave energy reduction over onshore fetch is a key factor in design of coastal infrastructure. Direct observation and estimation of the thickness of fluid mud on seafloors are complicated; this brings a major complication against accurate prediction of waves in muddy environments. As a step towards filling this gap, this study presents for the first time the estimation of the thickness of fluid mud layers surface waves generate over muddy shelves, using three methods : (1) a method based on vertical structure of acoustic backscatter that requires less assumptions, (2) a mass balance based on vertical structure of sediment concentration, and (3) an empirical approach. Comprehensive field observations of wave–mud interaction were collected for two months at 4 m water depth and analyzed here. The results, assumptions, and approaches of these three methods are evaluated. The analysis of the field observations and the estimates show that fluid mud layers formed in the wake of four significant frontal storms with relatively strong low-frequency swell energy (wave periods ≥ 7 s) during which the wave-induced orbital velocity at the bed exceeded the same threshold of ub∼ 0.5 m/s. The thickness of fluid mud layers varied between 4 cm and 15 cm among the four events. Using an onset density of fluid mud based on laboratory experiments, the mass balance method gives fluid mud thicknesses that agree with, but underestimating, the results of the acoustic backscatter method. The empirical approach agrees best with the acoustic backscatter method, when a settling velocity of 3.5 mm/s and a hydraulic roughness of 0.001 m are used, in agreement with the previous sediment and hydrodynamic data collected at the study site. Applicability of these methods to determine fluid mud thickness at other locations requires accurate description of sediment conditions near the seafloor under the influence of surface waves and hydrodynamics.

Seagrass roots strongly reduce cliff erosion rates in sandy sediments

Vegetated coastal ecosystems such as saltmarshes, mangroves and seagrass beds are increasingly promoted as sustainable storm and flood defence solutions by reducing wave energy. Yet, there is still intense debate on the ability of root mats to mitigate erosion, with some studies arguing that the direct contribution of roots in preventing sediment erosion is minor, while others consider them of major importance. Here, we hypothesized that the contrasting findings on the role of seagrass root mats in preventing erosion may stem from differences in sediment type. To test this idea, we investigated how root mats of seagrass that thrives in both sandy and muddy sediments mitigate wave-induced cliff erosion using Zostera marina in manipulative flume experiments. Results demonstrate that roots are very effective in reducing cliff erosion rates in sandy sediments. Cliff erosion rates were reduced up to 70% in sandy sediment with high seagrass root biomass. In contrast, cliff erosion rates in cohesive muddy sediments were low and unaffected by seagrass roots. This highlights the important role of seagrass roots in erosion mitigation, which has been overlooked compared to the role of canopies, which has received more attention. We suggest that management strategies should be developed to enhance the stabilization of sandy sediment, such as (1) using species with high belowground biomass, (2) using fast-growing pioneer species and (3) applying temporary stabilising measures.

Hyperspectral Image Mixed Denoising Using Difference Continuity-Regularized Nonlocal Tensor Subspace Low-Rank Learning

With the rapid advancement of spectrometers, the imaging range of the electromagnetic spectrum starts growing narrower. The reduction of electromagnetic wave energy received in a single wavelength range leads more complex noise into the generated hyperspectral image (HSI), thus causing a severe cripple in the accuracy of subsequent applications. The requirement for the HSI mixed denoising algorithm’s accuracy is further lifted. To address this challenge, in this letter, we propose a novel difference continuity-regularized nonlocal tensor subspace low-rank learning (named DNTSLR) method for HSI mixed denoising. Technically, the original high-dimensional HSI data was first projected into a low-dimensional subspace spanned by a spectral difference continuous basis instead of an orthogonal basis, so the data continuity of the restored HSI spectrum and tensor low-rankness was guaranteed. Then, a cube matching strategy was employed to stack the nonlocal tensor patches from the projected coefficient tensor, and a shrinkage algorithm was used to approximate the low-rank coefficient tensor. Eventually, the subspace low-rank learning algorithm was designed to alternately separate the noise tensor and restore the latent clean low-rank HSI tensor. Extensive experiments on multiple open datasets validate that the proposed method realizes the state-of-the-art denoising accuracy for HSI.

Numerical Study of Bamboo Breakwater for Wave Reduction

Flood inundation and shoreline erosion have long occurred in Sayung, Demak area, the northern coast of Central Java Province, Indonesia. The people of Sayung planted mangroves to reduce the flood inundation and shoreline erosion in that area. They built the bamboo array to protect the juvenile mangroves from incoming waves. The bamboo acts as a breakwater and is considered an environmentally friendly permeable structure to reduce wave energy and stimulate sedimentation. This paper discusses three bamboo arrays’ effectiveness in wave reduction using Numerical Wave Tank (NWT). The interaction of regular waves with a permeable structure comprising a single row of vertical circular poles was conducted based on the Smoothed Particle Hydrodynamics (SPH) method. The effect of different waves and structural dimensions on the permeable structure was investigated based on the structure’s transmission coefficient (Kt) performance. The investigations have revealed that structures with the combination of Vertical-Horizontal formation (VH) attenuate more wave energy than Vertical Only (VO) and the combination of Vertical-Diagonal formation (VD). As the wave steepness increases, the transmission coefficient decreases. Likewise, the transmission coefficient (Kt) is decreasing when the wave height is increasing. On the other hand, the transmission coefficient (Kt) increases as the wave period increases. As the structure spacing ratio between end-to-end and center-to-center spacing (e/S) rises, the transmission coefficient (Kt) also increases. The diameter (D) has a slight effect on the transmission coefficient (Kt). However, the center-to-center spacing (S) has a more significant impact than the diameter on the transmission coefficient, affecting an inclination on the transmission coefficient (Kt) when center-to-center spacing (S) goes up.

Efek Koefisien Transmisi akibat Variasi Wave Stepness pada Hexagonal Artificial Reef

Waves that move towards the coast have an energy level that corresponds to the magnitude of the generating force. Waves with high energy intensity are dominantly destructive when they hit the coastal area. In order to reduce the destructive effect of waves, coastal protection structures are needed to dampen the wave energy. Artificial coral reef (artificial reef) is one type of structure that can reduce wave energy. Besides functioning as an artificial reef for marine ecosystem biota, but also as a submerged breakwater structure. This study was conducted to determine the relationship between wave stepness and the transmission coefficient produced by hexagonal artificial reefs with a model scale of 1:10. The test is carried out using regular waves with a range of H/gT2 values between 0.0007 – 0.006. The results of research conducted at the Marine Energy Laboratory of the Department of Marine Engineering, FTK ITS, show that an increase in the value of wave steepness correlates with an increase in the value of the transmission coefficient (Kt) for all tests and configurations. The 1D structure configuration has a lower transmission coefficient (Kt) than the 0D structure configuration for each variation of the test wave.

Wave Attenuation Analysis for Artificial Coral Reefs Using a Physical Modelling Approach

Kim, T.; Kwon, Y.; Hong, S.; Kim, J.; Kwon, S., and Lee, J., 2021. Wave attenuation analysis for artificial coral reefs using a physical modelling approach. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 529–533. Coconut Creek (Florida), ISSN 0749-0208. Due to global warming and coastal development, the damages in coastal such as sea level rise and changes in coastline caused by scour and erosion are increasing, Various types of breakwaters are applied to prevent the coastal erosion, however, the problem such as scour around the structure is exacerbated, therefore a fundamental solution is needed. In this study, two-dimensional laboratory experiments were conducted in the wave flume to investigate the wave transmission phenomena of artificial coral reef. Experiments are conducted by analyzing wave transmission dependents on ratio of stem length to water depth(ls/h), wave height and wave period. Wave attenuation appeared to be most dependent on stem length to water depth(ls/h) and structure width. As incident wave height increased and the wave period decreased, the wave attenuation also increased, however, it was insignificant compared to the influence of the inundation rate. Wave attenuation increases dependents on incident wave height and period, however showed insignificant effect compared to submergence rate. In addition wave attenuation rate also affects wave energy reduction in order of ls/h > H0/h > h/L0. Based on results, we analyzed correlation between KC and CD of artificial coral reef to suggest the equation on empirical relationship. As a result, it is judged that estimating wave transmission rate and drag coefficient of artificial coral reef dependents on sectional specification can be utilized properly in working design and application.

Physical and Numerical Simulation of Wave Transmission Over Submerged Breakwater

Nowadays, the submerged breakwaters are becoming attractive to the coastal engineer because they have many advantages including keeping aesthetic value of coastal scenery and reasonable for wave energy reduction. However, on the other hand, their design is very complicated. So, it is very important to understand the characteristics and the impact of wave because of the submerged breakwaters. For this purpose, we developed both numerical and physical model for simulation of wave over submerged breakwaters. The numerical model was developed using CADMAS-SURF, which is widely used in a practice of business in Japan. Physical model studies were performed at the Coastal Engineering Research Laboratory, University of Miyazaki, Japan to assess the performance of submerged breakwaters under a wide range of design conditions. The tests include the use of single and double submerged breakwater, as well as the impact of interval between the breakwaters which will be useful references for submerged breakwater designing in the future. The results show that the transmission coefficients of the numerical simulation have a good agreement with the experiment result with the RMS error 0.14 and 0.19 for the single and double breakwater respectively. This study found that, the application of double breakwaters has no significant impact for reducing wave energy compared to the single breakwater for the wave steepness higher than 0.007 and 0.012 based on laboratory and numerical simulation respectively. The best relative breakwater spacings are 0.75, 0.4, 0.45 and 0.35 for any kind of wave with the period of 0.6, 0.8, 1.0 and 1.2 respectively. In those conditions, the transmission coefficients are on minimum value for each kind of wave, that means the double breakwaters have the good performance on energy reduction.

Not just an engineering problem: The role of knowledge and understanding of ecosystem services for adaptive management of coastal erosion

Coastal ecosystems are recognized as important providers of ecosystem services such as carbon storage, increased fish productivity, and wave energy reduction. In a context of climate change, coastal ecosystems are exposed to erosion and subject to coastal squeeze, even as they provide natural coastal protection against extreme weather. While civil engineering solutions often take centre stage in mitigating coastal erosion and protecting infrastructure from storms and sea level rise, we seek to explore the social dimension of adaptive management of socio-ecological systems and more specifically the role of knowledge and learning. Using an ecosystem services (ES) framework, we provide a first evaluation of local stakeholders’ perceptions of coastal habitats in maritime Quebec. The findings demonstrate the importance of a social approach for coastal ES valuation, in particular in addressing the complex question of cultural ES. A better understanding of the links between coastal stakeholders and their natural environment can help decision-makers and practitioners design conservation management and coastal adaptation measures mainstreaming the role of coastal habitats. Nevertheless, a change towards a socio-ecological perspective will require long-lasting processes that build on social capacities, such as flexible institutions and multilevel governance systems.

Wave Runup for Nowshahr Breakwater at Tide and EBB Scenarios

This study investigates runup design at breakwaters and design criteria under tidal and ebb scenarios for both head and truck of Nowshahr breakwater. First part includes runup height calculations based on shore protection manuals. Based of wave height, frequency, and water depth at the toe runup height has been calculated and Second portion has been dedicated to design of head and truck of Nowshahr port based on Hudson stability formula. Collision of wave and the breakwater head, results in immediate reduction in wave energy. As wave energy propagated gradually decreases when it meets the trunk. The results showed that in both conditions weight of head would be higher than the trunk of breakwater. while, both head and trunk are designed based on high strength materials, but the head has higher degree of importance in terms of design criteria. Hudson formula is responsible for the stability of breakwater structure. Tidal case which considers a non-breaking wave as well as ebb scenario including a breaking wave has been studied to include two extreme conditions occurs to breakwaters. The results showed the higher weight of head is responsible for stability of breakwater at both conditions.

Green infrastructure for the reduction of coastal disasters: a review of the protective role of coastal forests against tsunami, storm surge, and wind waves

ABSTRACT Green infrastructure, utilizing coastal ecosystems, provides a nature-based solution to counteract coastal hazards and rising sea level. Coastal forests, a major type of green infrastructure, are recognized as natural barriers against ocean waves. They can attenuate waves, mitigate erosion, and stabilize shorelines. With growing interests in coastal forests and their function of adapting to future risks, many researchers studied vegetation effects in coastal protection. Yet our limited expertise in quantifying vegetation-induced resistance limits the practical applications. This paper aims to review and categorize the studies related to wave attenuation and mitigation of sediment erosion by coastal forests and identify the potential directions in future works. We first reviewed field observations of extreme tsunami and weather events which showed the effectiveness of coastal forests in reducing wave energy. Next, we covered the studies on wave–vegetation interaction, including mathematical/numerical models and laboratory tests. We categorized the developed models based on different governing equations and introduced how vegetation effects were incorporated. We also discussed the experiments and vegetation models used in laboratory tests. Besides, we highlighted recent studies on the mitigation of coastal erosion. Finally, we recommend the potential directions to quantify the effects of coastal forests on wave attenuation and sedimentation.

A laboratory study on wave transmission over hexagonal artificial reef

Artificial reefs are commonly used to rehabilitate natural coral reef damage. Artificial reef serves as a new habitat for marine life and simultaneously protect the shoreline by reducing wave energy without reducing the aesthetics of the protected beach. As an artificial reef can serve as submerged breakwaters, the level of their effectiveness in reducing incoming wave need to be investigated. The new form hexagonal shape artificial reef is proposed then evaluated based on the transmission coefficient. The tests for various configurations of a hexagonal reef in a 1:10 scale were conducted in the wave flume of Department Ocean Engineering, Institut Teknologi Sepuluh Nopember, Surabaya. The result of tests was presented and showed that the new proposed hexagonal shape artificial reefs have better performance compared to cylindrical and cubical shape artificial reefs.

Development of a benthic spatial ratio index as an indicator of small island deformation

The ability of coral reefs and seagrass beds to reduce wave energy positions these ecosystems as the most reliable natural protection for many small islands, especially for coral islands and atolls. With coral damage reaching 174 hectares per year, there must be changes in the spatial composition of coral reefs and seagrass beds around many small islands in the Spermonde Archipelago, changing the shape of the islands and reducing the quality of life of their inhabitants. This study aimed to map the spatial composition of benthic substrates (coral reefs, seagrass beds, and macroalgae) around small islands over time, and to relate changes in substrate composition to island shape change. The initial study was conducted at Barrangcaddi island from July to December 2018. Three field surveys collected spatial data on benthic substrates (coral, seagrass, macroalgae), bathymetry, waves, tides, and beach profiles. The satellite data used were Sentinel 2 images from 2015 to 2018. Satellite image processing included atmospheric correction using the DOS method, land masking, geomorphic segmentation, and classification using the maximum likelihood, Self Organizing Map and Segmentation methods. Thirteen benthic substrate classes were validated with thematic accuracy ranging from 86% to 95%. The land area of Barrangcaddi Island changed around 6 percent from 2015 to 2018. The benthic spatial ratio index for Barrangcaddi Island shows that the north side of the island was the most vulnerable to coastal abrasion, and the existing benthic substrate is no longer effective in reducing the wave energy that hits the island from this side.

Ribbed mussel Geukensia demissa population response to living shoreline design and ecosystem development

AbstractCoastal communities increasingly invest in natural and nature‐based features (e.g., living shorelines) as a strategy to protect shorelines and enhance coastal resilience. Tidal marshes are a common component of these strategies because of their capacity to reduce wave energy and storm surge impacts. Performance metrics of restoration success for living shorelines tend to focus on how the physical structure of the created marsh enhances shoreline protection via proper elevation and marsh plant presence. These metrics do not fully evaluate the level of marsh ecosystem development. In particular, the presence of key marsh bivalve species can indicate the capability of the marsh to provide non‐protective services of value, such as water quality improvement and habitat provision. We observed an unexpected low to no abundance of the filter‐feeding ribbed mussel, Geukensia demissa, in living shoreline marshes throughout Chesapeake Bay. In salt marsh ecosystems along the Atlantic Coast of the United States, ribbed mussels improve water quality, enhance nutrient removal, stabilize the marsh, and facilitate long‐term sustainability of the habitat. Through comparative field surveys and experiments within a chronosequence of 13 living shorelines spanning 2–16 years since construction, we examined three factors we hypothesized may influence recruitment of ribbed mussels to living shoreline marshes: (1) larval access to suitable marsh habitat, (2) sediment quality of low marsh (i.e., potential mussel habitat), and (3) availability of high‐quality refuge habitat. Our findings suggest that at most sites larval mussels are able to access and settle on living shoreline created marshes behind rock sill structures, but that most recruits are likely not surviving. Sediment organic matter (OM) and plant density were correlated with mussel abundance, and sediment OM increased with marsh age, suggesting that living shoreline design (e.g., sand fill, planting grids) and lags in ecosystem development (sediment properties) are reducing the survival of the young recruits. We offer potential modifications to living shoreline design and implementation practices that may facilitate self‐sustaining ribbed mussel populations in these restored habitats.

The effect of square submerged breakwater on wave transmission in the coastal area

A transmission wave is a transmission wave that passes through an obstacle where its parameter can be expressed as the ratio of the transmitted wave height (Ht) to the incident wave height (Hi). Waves can occur due to wind, tides, artificial disturbances such as ship movements and earthquakes. To reduce wave energy coming from the high seas, a breakwater can be installed. The breakwater is a building that functions to break the waves of sea water, thereby reducing the energy in sea water waves. The aim of this research is to understand the wave transmission with an asymmetrical sinking structure with a square shape which is varied with respect to the length of the model. This research was conducted with a sinking square-shaped breakwater model. The results of this study indicate that the size of the transmission coefficient is influenced by the length of the model and the water depth of the sinking breakwater model. The longer the model arrangement installed, the greater the transmission coefficient, as if the water depth increases, the transmission coefficient will also increase.

WAVE TRANSFORMATION WITHIN A CORAL REEF LAGOON SYSTEM, ERAKOR LAGOON, VANUATU

Coral reefs encircle most of the islands in Vanuatu and provide natural breakwaters for coastal communities by reducing wave energy arriving at the shoreline acting to control both inundation and erosion. Climate Change is projected to both exacerbate coastal hazards and endanger corals. The aim of this paper is to better understand the parameters that govern hydrodynamics on fringing reef systems. The interaction between the depth, waves and currents are studied from measurements conducted in Erakor lagoon, Vanuatu.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/mPrG6NWL4dM

Reduction of Wave Energy Due to Monotypic Coastal Vegetation Using Response Surface Methodology (RSM)

Reduction of Wave Energy Due to Monotypic Coastal Vegetation Using Response Surface Methodology (RSM)