Coastal Engineering Research Articles

LOW-CRESTED AND EMERGENT BREAKWATERS WITH ECO-FRIENDLY ARMOUR UNITS

Artificial coastal defense systems (such as concrete armour units) frequently host less diverse aquatic populations than natural environments and feature higher concentrations of invasive species (Dafforn et al., 2009). Therefore, coastal structures need to be designed or refitted to achieve sustainable goals through the application of ecological engineering solutions applied to coastal defence structures and for the ecosystem, marine habitat, and biodiversity improvement. Ecological engineering, which integrates ecosystems with engineering principles to construct coastal structures that benefit both humans and the ecosystem, is growing as a means of reducing the adverse ecological impacts of coastal infrastructure (Mitsch & Jorgensen, 2003). Thus, creating new eco-friendly breakwater design guidelines is critical and will benefit from the multidisciplinary involvement of marine biologists and ecologists. The purpose of this experimental modelling study was to provide data on the hydraulic performance and stability of low-crested and emergent rubble mound breakwaters (RMBW) constructed using ecologically friendly armour units under various wave conditions. The University of Ottawa, the National Research Council of Canada (NRC), and ECOncrete collaborated to develop and conduct the physical testing program. Several breakwater models were tested to evaluate their performance, as the idea of an eco-friendly breakwater is still a new area of research. Thus, this experimental program is essential to promote environmentally-friendly armour units in the design of new coastal structures (such as Baker et al., 2018), as well as ecological retrofitting of existing coastal structures. The physical tests were conducted between June 2023 and August 2023 in the Large Wave Flume of NRC’s Ocean, Coastal, and River Engineering Research Center in Ottawa, Canada. ECOncrete's Coastalock armour units were tested in various configurations at a 1/15 scale using two-dimensional low-crested and emergent RMBW models. The hydraulic performance and failure mechanisms of these environmentally-friendly breakwater models were tested under severe wave conditions.

Innovative Coastal Structure Solutions And The Role Of Physical Modelling In The Design Process (Dawlish Mog2 Casino)

With the increase in storminess due to climate change induced sea level rise, coastal protection solutions need to be able to contend with larger storms, resulting in larger incident waves, on a more regular basis. Many traditional coastal protection systems like vertical seawalls are proving to be expensive to design for the increased overtopping associated with this change in coastal conditions. As such, engineers are developing more bespoke and innovative design solutions, such as the use of bullnoses and the use of multiple seawalls located one behind the other. Examples of the former can be found in the new Dawlish seawall (see Figure 1) built to replace the old seawall that was damaged during a storm surge in February 2012. For the later, recent examples include the Middelkerke CASINO stilling basin (see Figure 2) and the new energy island being developed by Elia in Belgium (MOG2). The latter consists of two vertical seawalls (see Figure 3), each with a bullnose to reduce overtopping rates. CASINO and MOG2 have in common the novel approach of allowing significant overtopping of the first seawall but instead using the second wall as the safety line, to ensure safe overtopping limits are achieved at this location, thus reducing the required height of the front wall. Moving towards alternative design solutions is associated with its own set of design challenges. The primary challenge is the lack of consistent design guidelines within the field of coastal structures. In Europe, EurOtop is commonly used for overtopping estimates in design (van der Meer et al., 2018). In the US, the Coastal Engineering Manual is used instead (USACE, 2002). Both of these guidelines rely on empirical equations and the variations between the two are primarily a question of preference. However, the empirical equations can have large variations in their solutions (a factor of 3 for the overtopping rate is commonly accepted), the value of which can be heavily dependant on the geometric configuration being used for the seawall, toe protection and bathymetry, limiting their applicability to novel solutions. There is limited research currently available investigating novel geometries such as bullnoses (Dong et al., 2021, Castellino et al., 2018) and stilling basins, and much of the existing literature is limited in scope, thus limiting its wider applicability. In the case of MOG2 and CASINO, the use of the two seawall configuration, combined with drainage solutions, means that there is no suitable guidance in neither of the aforementioned design guides. As a result, coastal designers often turn to physical modelling in order to identify the specific design loads and overtopping values of their proposed design. Physical modelling performed in collaboration with research organisations allows design engineers to benefit from the expertise of researchers working with state-of-the-art techniques informed by the most recent research. However, the physical modelling phase is often not fully integrated into the design process meaning that is it not fully utilised. Integrating physical modelling fully into the design cycle can help to optimise the design as well as identifying the structural loading and verifying the overtopping performance.

Arctic Coastline Erosion: Novel Experimental Avenues Help Understand Its Response To A Changing Climate

Permafrost coastlines represent a large portion of the world’s coastal area and these areas have become increasingly vulnerable owing to the changing climate and its strong dynamics observed over the past decades (Irrgang et al., 2022). The predominant mechanism of coastal erosion in these areas has been identified through several observational studies as thermomechanical erosion—a joint removal of sediment through the melting of interstitial ice (thermal energy) and abrasion from incoming waves (mechanical energy). Longer summer seasons where -due to a much lower ice cover- waves can more freely propagate towards Arctic coastlines have exacerbated coastal erosion (Overeem et al., 2011) and which is projected to increase inline with Arctic warming (Nielsen et al., 2022). Erosional effects have long been a subject of the coastal engineering community, however, the combined effect of wave attack on shorelines, in combination with thermomechanical processes has largely been overlooked. The implications of Arctic coastline erosion are plenty: local communities face relocations of whole settlements, loss of valuable property or cultural heritage while acceleration in thaw causes a much higher influx of environmental contaminants and nutrients into the Arctic Ocean. It is hence crucial to engage this pressing challenge with long established and novel methods originating from the coastal engineering community. This work provides an overview over novel avenues that are useful for a better understanding of the processes and interactions of ocean waves and Arctic coastlines. It also presents some of the recent erosional observations from a cold room flume and micro CT measurements.

Large-Scale Experimental Model Of Edge Treatments For Constructed Salt Marshes

Large stretches of Canada’s coastlines are lined with legacy dykes (or levees) to provide protection against coastal flooding and erosion. However, future sea-level rise presents a risk to these structures, which may result in the dykes being under designed when exposed to future water levels and wave conditions. Under certain conditions, these dykes can be augmented with a coastal saltmarsh to create a living dyke, which allows for the existing dyke to be more resilient against sea level rise without the need to retrofit the dyke with a higher crest elevation or larger armour stone. The coastal saltmarsh is able to attenuate storm waves, resulting in lower wave energy at the dyke, while also attracting and retaining sediment to combat coastal erosion. The Living Dyke project in Boundary Bay, Canada is a pilot project being used to test the living dyke concept by placing sediment and planting salt marsh vegetation in the foreshore combined with upgrades to the existing dyke. Kerr Wood Leidal Associates Ltd. prepared a preliminary design which incorporated four different edge treatment features that are to be installed at the offshore edge of a newly constructed salt marsh platform in order to attenuate wave energy and retain the placed sediment before the planted vegetation can be established. The proposed edge treatment features included a natural sand edge, a rounded gravel berm, an oyster-shell filled bag berm, and a brushwood dam. Large scale (full scale for all edge treatment feature tests except for the brushwood dam which was conducted at half-scale) physical model experiments were carried out by the National Research Council of Canada’s Ocean, Coastal and River Engineering Research Centre in their Large Wave-Current Flume to investigate the performance, including stability of the edge treatment features, wave attenuation ability, and stability of the salt marsh platform, of these edge treatment features under varying water level and wave conditions that are present at Boundary Bay.

Validation Of An Efficient Non-Hydrostatic Wave Model As A Design Tool For Foreshores In Physical Models

In the design of physical model experiments in coastal engineering, it is common that the construction of a foreshore is necessary to obtain the desired wave conditions at a given location, usually close to a structure being tested. In addition to the commonly used spectral wave parameters to describe the target wave conditions, the wave height distribution and associated parameters (such as Hmax and H2%), wave periods and infra-gravity waves can be important to reproduce properly as well. Wave height distributions are typically important for tests where e.g. wave run-up or wave forces are of interest. Since the construction of foreshores is labour intensive (and thus expensive), it is useful to be able to check a priori whether the target wave conditions are met with a given foreshore design and whether the chosen transition slope does not significantly influence the wave conditions. One way to do this is by using numerical wave models. For a numerical model to be a useful design tool for physical model layouts, the predicted wave transformation (over the foreshore) needs to be sufficiently accurate. One option is to use detailed CFD wave models for this purpose, such as OpenFOAM, which has been shown to accurately reproduce wave transformation (Jacobsen et al., 2015; Jacobsen et al., 2018). CFD models, however, typically feature high computational demand and consequentially computational times in the order of days. This is a significant disadvantage in the context of designing a physical model experiment, for which the layout and configuration is often an iterative process, which would be hampered by overly long computational times. On the other hand, spectral wave models, like SWAN (Booij et al., 1996), are much faster but do not model all the individual waves rendering it unable to model exceedance distributions. As a middle-ground, it seems that the XBeach model (Roelvink et al., 2009) used in its 2-layer non-hydrostatic mode (De Ridder et al., 2021) might present a workable compromise between computational time and accurate representation of the wave transformation. The model has been validated by De Ridder et al. (2021) on bichromatic waves, complex barred beach geometry and a fringing reef for bulk wave parameters and spectral properties. Expanding on earlier validation work, in this work the ability of the XBeach 2-layer non-hydrostatic model (XBeach-nh) to reproduce wave height exceedance distributions over a sloping foreshore is validated using wave flume data, described in Sections 2 and 3. The preliminary results of the validation effort are shown in Section 4.

Analysis of basalt fiber reinforcement on static shear properties of Beibu Gulf sea sand

Basalt fibers are a reinforcing material with excellent mechanical properties and durability. In contrast, although Beibu Gulf sea sand is widely in engineering, it exhibits low strength and poor stability, which can be improved by adding basalt fibers. In this study, the effects of fiber content, fiber length, and effective confining pressure on the static shear strength of fiber-reinforced sea sand were investigated using a triaxial shear test. The maximum improvement on the static shear characteristics and deformation resistance of sea sand were achieved for a fiber content and length of 0.8% and 12 mm, respectively. The cohesion and internal friction angle of sea sand were improved and the secant modulus and strain before and after basalt fiber reinforcement showed a nonlinear attenuation tendency. The reinforcement effect coefficient R and the basalt fiber content under different dosages were in accordance with the law of the Gaussian function. The value of R conformed to a linear growth and exponential function law under different fiber lengths and effective confining pressures, respectively. This study provides a solid theoretical basis for the sustainable utilization of sea sand resources and fiber reinforcement for road and coastal protection engineering in the Beibu Gulf region.

Some novel different solutions for Boussinesq-type models including bright, singular, and dark soliton ones

Some new different kinds of one-soliton solutions for various forms of Boussinesq-type equations are presented in thispaper to describe the nonlinear wave phenomena in coastal and ocean areas such as tsunami waves. These one-solitonsolutions include bright, dark, and singular ones. The property of each solution in coastal and ocean engineering isexplained.

Coastal Erosion and Engineering Solutions along Visakhapatnam Coastline East Coast of India

Coastal Erosion and Engineering Solutions along Visakhapatnam Coastline East Coast of India

Enhanced corrosion protection of rebars in alkaline solutions by ferroporphyrin and the mechanisms of electron consumption and lattice reconstruction

Abstract Reinforced concretes are the primary materials in coastal and offshore engineering. In alkaline environment of concrete, the anodic process is passivation of rebars and the conjugated cathodic process is oxygen reduction reaction (ORR). It is proposed that a novel approach to enhance the passivation films through catalyzed ORR by iron meso-tetra(4-carboxyphenyl)porphine (FeTCPP). The ORR catalyst FeTCPP promotes the formation of passivation film, as it accelerates the consumption of abundant electrons generated and accumulated by the anodic formation of passivation films. The passivation films of rebars are highly defective Fe3O4 semiconductor. The dissolution of interstitial ferrous ions and lattice iron ions produces defects of O ion vacancies, Fe ion vacancies and interstitial Fe ions, and they further cause the formation and accumulation of Fe atom vacancies on the metal surface, leading to the collapse of the passivation films. The FeTCPP adsorbs on the surface of passivation films, hindering the dissolution of lattice iron ions and interstitial ferrous ions, thereby inhibiting the generation and accumulation of Fe atom vacancies and improving the integrity and protective ability of the passivation films.

Turning The Tide: Live-Bed Scale Experiments Of Bar-Dominated Estuaries And Effects Of Dredging On Intertidal Habitat

Many large sand-dominated estuaries and tidal basins have complex channel and bar patterns, wherein a continuous deep channel suitable for shipping is rarely naturally present, which requires dredging. The intertidal area has important, often protected habitats for macro-benthic species, wader birds and other species. The question is to what degree channel and shoal dimensions and the amount of intertidal area are affected by dredging and disposal for access to ports. While numerical modelling is conducted for these systems with some success, complementary scale experiments with live beds have challenged the fields of coastal engineering and coastal morphodynamics for over a century. Compared to scale models for rivers, the scale issues in tidal experiments are more complicated and very few attempts have been pursued. For example, Reynolds (1889) conducted the first scale experiments of an estuary by a periodic sea level fluctuation, but found that even fine sand was hard to mobilize, while the bed surface was dominated by ripples rather than bars. Similarly, Tambroni et al. (2005) carefully scaled sediment mobility in a converging channel and obtained large-scale morphological patterns with gentle bars nearly overwhelmed by ripples. Stefanon et al. (2010) present a careful attempt at erosive tidal channel network development in a scale model with low-density sediment, which showed unexplained, over-large scour holes at channel junctions. The key issues for tidal experiments are to obtain sufficient sediment mobility (expressed as Shields or Rouse number) and to avoid over-large ripples and scours, and to this end classic river scale modelling is inadequate. Here we assess whether our recent innovation solves these scale issues. The objective of this abstract is to elucidate the scaling of experiments that enable study of morphodynamic estuaries in many aspects including effects of sediment management by dredging.

Stability Of Concrete Armor Unit (Tetrapod) On Rear Side Of The Rubble Mound Structures With Rectangular Super Structure

The coastal structures allow the wave overtopping within a certain quantity. However the extreme wave overtopping could cause the damage of coastal structures. The most of the previous researches for the stability of armor unit were performed about the armor units placed on sea side of coastal structures. A rubble-mound structure is normally composed of a bedding layer and a core of quarry-run stone covered by one or more layers of larger stone and an exterior layer or layers of large quarry stone or concrete armor units. Coastal Engineering Manual (USACE, 2006) suggested the design figures without super structures and showed the ratio of the armor weight for each location of rubble mound structures and it could be known that the same weight ratio was needed to the sea side and harbor side slope of rubble mound structures. In this design figure, the filter rule is applied to the design figures of CEM, that is, the weight ratio for under layer is W/10 for the main armor weight ratio (W) to prevent smaller rocks in the under layer from being pulled through an over layer by wave action

Reliability-Based Design Optimization for a Vertical-Type Breakwater with an Emphasis on Sliding, Overturn, and Collapse Failure

To promote the application of reliability-based design within the Korean coastal engineering community, the author conducted reliability analyses and optimized the design of a vertical-type breakwater, considering multiple limit states in the seas off of Pusan and Gunsan – two representative ports in Korea. In this process, rather than relying on design waves of a specific return period, the author intentionally avoided such constraints. Instead, the author characterized the uncertainties associated with wave force, lift force, and overturning moment – key factors significantly influencing the integrity of a vertical-type breakwater. This characterization was achieved by employing a probabilistic model derived from the frequency analysis results of long-term in-situ wave data. The limit state of the vertical-type breakwater encompassed sliding, overturning, and collapse failure, with the close interrelation between wave force, lift force, and moment described using the Nataf joint probability distribution. Simulation results indicate, as expected, that considering only sliding failure underestimates the failure probability. Furthermore, it was shown that the failure probability of vertical-type breakwaters cannot be consistently secured using design waves with a specific return period. In contrast, breakwaters optimally designed to meet the reliability index requirement of <i>β</i>-3.5 to 4 consistently achieve a consistent failure probability across all sea areas.

Armor Damage On Groins Under Ship Wave Attack Using Field Data

The severity of damages to riverine structures, such as groynes or revetments, across German estuaries has increased in the past years due to the increase in the ship-induced loads. However, few studies can be found in the literature focused on the damage of rock slopes under ship wave attack. In this study, the field data of a rock-armored groyne (lateral slope 1/4 and rocks with nominal diameter Dn50»12.6cm and high density ρs=3.7t/m3) tracked for a year by Melling et al. (2020) is analyzed; the field campaign began after the structure was rebuilt and finished when the structure already presented severe damage. During this field campaign, the incident ship-induced primary waves and water levels were recorded, and laser scans of the groyne armor were taken. Using those field laser scans, damage curves along the life of the structure were derived. Also, ship data from the AIS was retrieved. Then, each increment of the damage (increment of the dimensionless eroded area, ΔSe) was related to a ship-wave event and a passing ship. The most significant variable to describe ΔSe was found to be the primary wave height Hp, while the best explanatory variables for Hp were the partial blockage factor, the ship length and width and the relative velocity of the ship. The shape of the dependence between these variables is also analyzed by pairs using copula space. A clear tail dependence is observed between several pairs. For instance, the pair ΔSe and Hp presents upper tail dependence, meaning that the high values of ΔSe and Hp are more correlated than the smaller ones. This implies that models more complex than Gaussian copula, which is commonly used in Coastal Engineering applications, might be needed to model the probabilistic dependence between the variables.

Spectral Wave Characterization Of The Pacific Coast Of Costa Rica

The results of the analysis of the wave measurement campaigns on the Pacific coast of Costa Rica are presented. After analyzing more than 14000 spectral shapes from sea states, it has been determined that many of them present 2 or more swell peaks, so it was proposed to perform a wave characterization in which 8 different types of spectra were defined to include all the data collected. Also, verifications were carried out in these sea states to check the reliability of many of the approximations usually used in coastal engineering that assume narrow-band spectra, such as the JONSWAP type.

Sustainable And Bioengineered Concrete For Armor Units Of Low-Crested Structures

In the last two decades, Eco-engineering has emerged to mitigate and compensate the environmental impacts of man-made structures while integrates benefits to society, being concrete the most widely alternative material used to natural rocks for construction of artificial coastal structures. Over the past three decades, an extensive literature has documented different supplementary cementitious materials (SCMs) to reduce CO2 emissions from Portland cement, with common SCMs used in marine and coastal structures such as fly ashes, ground granulated blast furnace slags, pozzolanas and limestones. However, there is a need to further investigate the suitability of SCMs for the construction of Low-Crested Structures (LCS) to decrease carbon footprint from concrete production and improve the bioreceptivity of concrete armor units during the breakwater lifetime. A literature review conducted in this study shows several advantages of slag cements compared to other SCMs to reduce carbon emissions and enhance biological colonization and durability of concrete submerged in seawater, identifying surface roughness as the most effective factor in design of bioreceptive concrete. This study also highlights the importance of the type and quantity of cement used in concrete mixes to reduce carbon footprint of the manufacture of concrete armor units of LCS and the implementation of long-term monitoring plans to fully understand the functioning of local communities that develop on concrete surfaces of artificial structures, and thus, to improve the integration of environmental parameters in the field of coastal engineering.

50 Years Of Hanbar Concrete Units In Australia And New-Zealand: Lessons Learned From Physical Modelling Studies And Recently Built Structures

During the last 50 years, numerous breakwaters along the eastern coast of Australia, and more recently in New Zealand, have undergone construction, repairs, or upgrades using Hanbar concrete armour units. These units are distinct to Australasia, and there is limited information about their properties in standard coastal engineering literature. This paper first provides a survey and timeline of all known projects using Hanbars. An overview of the Hanbar concrete unit features and manufacturing method is then provided. The paper presents a summary of results of previous modelling studies of Hanbar applications to specific breakwaters, as well as recent research programs completed at WRL, and provides placement density guidelines as well as recommended damage coefficient (Hudson Kd) for design. The paper concludes with a brief overview of two recent case studies which have successfully capitalized on the economical, robustness and manufacturing simplicity of the Hanbar concrete units. The first case study is on the Opotiki Harbour Development (“OHD”) in New Zealand. The OHD scheme comprises twin 400 m long training wall breakwaters to train a dynamic river mouth. A multi-stage approach to physical modelling was adopted by conducting 2D modelling of key sections of the training wall trunks, quasi-3D modelling of the breakwater head, and full 3D modelling of complete structures. The second case study presents the results of a field trial investigating the potential for high-density geopolymer concrete (GPC) coastal armour units. This resulted in the casting and placing of thirteen 16 t GPC Hanbar units (SG 2.6) on the Port Kembla northern breakwater in NSW. The trial proved the viability of production of geopolymer armour units, and allowed long-term monitoring of the integrity of the concrete in the aggressive marine environment.

Directional Spectrum Estimation For Sea States Generated By The Single Summation Method

The influence of directional spreading of waves is significant for wave-induced loads, wave breaking and nonlinearity of the waves. For physical model testing performed at test facilities such as the Ocean and Coastal Engineering Laboratory at Aalborg University, it is crucial to validate if the test conditions match the target sea states by measurement and analysis of the generated directional wave field. Most of the existing methods assumes a double summation sea state to be present which is valid in the prototype. However, waves in the laboratory are usually generated by single summation. The current paper presents a method to analyse short-crested waves generated by the single summation method. Compared to similar methods oblique reflections are considered instead of only in-line reflections. The results show that the method successfully decomposes the incident and reflected wave fields in the time domain. Thus, for example the incident wave height distribution may be obtained. The sensitivity of the new method to additional reflective directions, noise, calibration errors and positional errors of the wave gauges was found small.

Prediction of Storm Surges in the East Coast of Peninsular Malaysia in Response to Climate Change

This study employed the MIKE 21HD modeling framework, integrating data from the future climate database, "Policy Decision Making for Future Climate Change (d4PDF)" on selected critical ensembles to investigate the impact of climate change on storm surge height (SSH) along the East Coast of Peninsular Malaysia during the Northeast Monsoon season. Three scenarios, including past-historical data, future climate with a 2°C increment (+2K), and future climate with a 4°C increment (+4K), were analyzed. The study had validated model accuracy through root mean square error (RMSE), demonstrating alignment with observed data. Results indicated a correlation between temperature increase and storm surge height (SSH), with higher temperature scenarios leading to more severe surge outcomes. The analysis identified the Future +4K scenarios as yielding the most critical SSH across all stations, with recorded SSH at Kuala Pahang (SSHmax = 1.379 m), Chendering (SSHmax = 1.344 m), Geting (SSHmax = 1.251 m), and Tanjung Sedili (SSHmax = 1.251 m) stations. Considering the findings, it was recommended to reassess the baseline provision for coastal engineering projects, suggesting a storm surge resilience design exceeding the observed maximum. The utilization of d4PDF data in this study laid the groundwork for targeted strategies to mitigate the impacts of climate-induced storm surges in vulnerable coastal regions.

Hydraulic Stability Of The New Cubilok™ Armour Unit On A 3:4 Slope

The Cubilok™ (or Cubilok) is a new trademarked armour unit that has been developed in South Africa by PRDW Consulting Ports and Coastal Engineers to accommodate a wide range of breakwater designs. The Cubilok is still in its early stages of development and therefore it has not yet been applied or tested in prototype conditions. 2D Physical model tests were conducted as part of a master’s research project to investigate the stability and behaviour of the Cubilok on a 3V:4H slope. From this study, it was observed that the wave steepness has a significant influence on the performance of the Cubilok, where superior stabilities were recorded during conditions with shorter wave periods. When placed on a 3V:4H slope and with a packing density of ɸ = 0.63, the stability of the Cubilok is comparable to that of other concrete armour units, however, it is susceptible to severe settlement. Some results also showed that the settlement of the armour layer can probably be significantly reduced when the armour layer is constructed on a milder 1V:2H slope or when the packing density is increased to ɸ = 0.65.

Simplified models of wind-wave relationships in China's shallow-water coasts based on SWAN+ADCIRC simulations

The study of the shallow-water wind-wave relationship holds considerable importance in the realm of coastal engineering construction. However, existing empirical formulas for China's coastal areas face predictive accuracy challenges due to the discontinuity and insufficient temporal and spatial resolution of conventional observations, such as buoy and satellite data. Therefore, this study emphasizes two representative shallow-water areas along China's coast, the Pearl River Estuary and Bohai Bay. Based on the advanced SWAN + ADCIRC wave-current coupling model, numerical models for calculating wave evolution are established, calibrated and validated by real observation data. From these numerical foundations, a new model capturing shallow-water wind-wave relationship is proposed, demonstrating substantive applicability specifically tailored to the estuary and bay regions. The accuracy and applicability of the model are validated by comparing with real observation data. In addition, probabilistic models are introduced in this study accounting for the randomness of the significant wave height. These enhancements allow for refined quantification of significant wave height occurrence probabilities relative to specified wind speeds, offering informed predictive parameters, including upper and lower limits.