Wave Run-up Height Research Articles

A brief history of tsunamis in the Vanuatu Arc

Abstract. The archipelagos of Vanuatu and the eastern Solomon Islands, scattered over 1500 km along the Vanuatu Arc, include dozens of inhabited volcanic islands exposed to many natural hazards that impact their populations more or less severely. Due to the location of these islands on a subduction interface known as the Vanuatu subduction zone, tsunamis triggered by earthquakes, volcanic eruptions, and landslides locally, regionally, and in the far field represent a permanent threat. If catalogues already list tsunamis that have occurred in the Vanuatu Arc, they were not exclusively focusing on this region. This study goes further in the listing of tsunamis reported and/or recorded in the Vanuatu Arc, analysing existing catalogues, historical documents, and sea-level data from the five coastal tide gauges located in Vanuatu at Port Vila (Efate), Luganville (Espiritu Santo), Litzlitz (Malekula), and Lenakel (Tanna) and in the eastern Solomon Islands province at Lata (Ndende). It allows the identification of 100 tsunamis since 1863, 15 of them showing wave amplitude and/or run-up height of more than 1 m and 8 between 0.3 and 1 m. While some tsunamis are known to have occurred in the past, information about the wave amplitude or potential run-up is sometime lost (15 events). Also, tsunamis reported in neighbouring islands like New Caledonia but not reported or recorded in the Vanuatu Arc are discussed, as well as debated events or events with no known origin(s).

Numerical Evaluation of Wave Dissipation on a Breakwater Slope Covered by Precast Blocks with Different Geometrical Characteristics

Slopes suffer damage from waves in coastal environments. Precast blocks with well-designed geometrical characteristics can benefit the construction of revetments by mitigating the issue of wave overtopping and dissipating wave energy. In this study, we numerically studied the effect of the geometrical characteristics of precast blocks on wave overtopping by carrying out a numerical simulation of wave overtopping on a slope covered with precast blocks. A total of three different types of blocks were considered in this study to determine the optimal geometric shape using a validated numerical model. Our numerical investigation demonstrated that the roughness of the precast block plays an important role in lessening the height of the wave run-up. Concave and embedded regular hexagons could reduce the wave run-up height by 44.6% compared with smooth slopes within a 2 s wave period. Herein, we evaluate and discuss the influence of the geometrical characteristics of a given precast block, such as thickness, aperture, and wave dissipation notch, on wave run-up. We also present an empirical formula for predicting wave run-up on a slope covered by a concave and embedded regular hexagon-type prefabricated block. This study provides valuable insights into the design of prefabricated revetment blocks.

Characterization of Seismic Signal Patterns and Dynamic Pore Pressure Fluctuations Due to Wave-Induced Erosion on Non-Cohesive Slopes

Wave erosion of slopes can easily trigger landslides into marine environments and pose severe threats to both the ecological environment and human activities. Therefore, near-shore slope monitoring becomes crucial for preventing and alerting people to these potential disasters. To achieve a comprehensive understanding, it is imperative to conduct a detailed investigation into the dynamics of wave erosion processes acting on slopes. This research is conducted through flume tests, using a wave maker to create waves of various heights and frequencies to erode the slope models. During the tests, seismic signals, acoustic signals, and pore pressure generated by wave erosion and slope failure are recorded. Seismic and acoustic signals are analyzed, and time-frequency spectra are calculated using the Hilbert–Huang Transform to identify the erosion events and signal frequency ranges. Arias Intensity is used to assess seismic energy and explore the relationship between the amount of erosion and energy. The results show that wave height has a more decisive influence on erosion behavior and retreat than wave frequency. Rapid drawdown may potentially cause the slope to slide during cyclic swash and backwash wave action. As wave erosion changes from swash to impact, there is a significant increase in the spectral magnitude and Power Spectral Density (PSD) of both seismic and acoustic signals. An increase in pore pressure is observed due to the rise in the run-up height of waves. The amplitude of pore pressure will increase as the slope undergoes further erosion. Understanding the results of this study can aid in predicting erosion and in planning effective management strategies for slopes subject to wave action.

Numerical study on hydrodynamic impacts of 3D excavation pit on tsunami-like wave at fringing reef

In recent years, dredging reef sand and aggregate as building materials for infrastructures has become a common practice in many atoll islands, which can significantly reshape the wave hydrodynamic environment at the fringing reef. Hence, it becomes necessary to evaluate the hydrodynamic impacts of excavation pits at fringing reef. However, previous research adopted a simplified two-dimensional (2D) excavation pit model, which ignores the influences of 3D geometric characteristics of excavation pit. This study performs a three-dimensional (3D) numerical study on the hydrodynamic impacts of 3D excavation pit on tsunami-like wave at fringing reef by using a nonhydrostatic wave model (NHWAVE). Impacts of several main factors, such as water depth, wave height, pit location, geometric dimensions of pit, the spacing between two serially connected pits and the spacing between two parallel connected pits are carefully discussed. Research results reveal that 3D excavation pit can significantly reshape the wave hydrodynamic environment at the fringing reef, especially the local wave height at the pit. In addition to wave breaking at the reef edge, the 3D excavation pit can further damp out a portion of energy of the breaking surge bore, which can reduce the maximum value of wave runup height at centerline of computational domain. However, maximum value of wave runup height near the two sides of pit are slightly increased to some extent.

Optimization of stepped revetment configuration on minimizing wave run-up and overtopping

A stepped revetment has proven to be able to attenuate wave run-up height and wave overtopping discharge more effectively than a dike or a smooth-slope revetment does. However, the investigation into the optimal design of a stepped revetment, tailored to different wave and coastal conditions, is notably lacking. This paper introduces a computational model developed from the non-linear shallow water equations and the Genetic Algorithm. The aim is to optimize the width of a stepped revetment's step and crest, considering wave run-up and overtopping as key parameters. Multiple benchmark tests were conducted to validate the model's accuracy in estimating wave run-up and overtopping for specific setups. The results demonstrate a strong correlation between the numerical findings and experimental data. The Genetic Algorithm was then employed to predict the optimal step width for minimizing wave run-up height and determining the optimal step and crest widths to reduce wave overtopping discharge to an acceptable level. The findings reveal that for a gently sloping stepped revetment, the optimal step widths, based on wave run-up, remain relatively consistent across different wave heights. In contrast, when optimizing for wave overtopping, the optimal step width tends to fluctuate in most cases, although it shows some consistency in certain scenarios.

Numerical investigation of infragravity wave hydrodynamics at fringing reef with a permeable layer

In tropical and subtropical coastal regions, coral reefs are abundant and play a vital role in maintaining ecosystem balance. Additionally, they effectively dissipate a significant amount of wave energy that propagates from the open sea towards the coastline, providing coastal areas with protection against wave impacts. Consequently, numerous scholars have conducted extensive research to investigate the hydrodynamic characteristics of wave propagation and transformation over coral reef topography. However, previous studies have often simplified the bottom boundary of coral reefs as impermeable layers, neglecting the fact that the coral reef consists of a permeable canopy structure in the actual marine environment. To fill the knowledge gap of previous research, this study is based on the Non-Hydrostatic Wave Model Solver (NHWAVE) to numerically simulate the propagation process of random waves over permeable coral fringing reefs. The study takes a comprehensive approach by considering the influences of various factors on the hydrodynamic characteristics of random waves over the fringing reef, including incident wave height, reef-flat water depth, peak wave period, permeable layer thickness, permeable layer porosity, and median diameter of the permeable layer. This paper focuses primarily on analyzing the variations in sea-swell wave height (HSS), infragravity wave height (HIG), and mean water level (MWL) along the fringing reef, while conducting a comparative analysis between fringing reefs with a permeable layer and impermeable fringing reefs. The findings reveal that the presence of a permeable layer reduces the shallow water deformation of waves on the fore-reef slope and mitigates the wave-breaking phenomenon near the reef edge, thereby significantly reducing the sea-swell wave height (HSS), infragravity wave height (HIG), and wave setup on the reef-flat. Furthermore, the permeable layer's existence also leads to a decrease in the maximum wave run-up height on the back-reef slope. The research findings of this study can further enhance our understanding of the hydrodynamic characteristics of infragravity waves over fringing reefs, which is significant for studying the impact of random waves on coastal areas and understanding the protective mechanisms of coral reefs in coastal regions.

Evidence of Middle Holocene landslide-generated tsunamis recorded in lake sediments from Saqqaq, West Greenland

Abstract. The Vaigat strait (Sullorsuaq) in West Greenland is well known for its susceptibility to landslides and historical landslide-generated tsunamis. Recent mapping of the seabed in the Vaigat strait has revealed several prehistoric giga-scale (volumes of 109 m3) tsunamigenic landslides. However, the timing of these giga-scale tsunamis is largely unconstrained, but they are assumed to have occurred after the last deglaciation. Here, we report on lake sediment core records from four coastal lakes located between 19 and 91 m above sea level (a.s.l.) on the Saqqaq foreland at the eastern end of the Vaigat strait. We use a multiproxy approach including X-ray fluorescence (XRF) and magnetic susceptibility core scanning along with a screening for marine diatoms to identify at least two tsunami deposits in two of the four sediment cores. Radiocarbon dating of aquatic macrofossils and bulk samples suggest that the tsunami events occurred at ca. 7.6 and 7.3 ka cal BP. Using a previously published relative sea level curve from Vaskebugt, Arveprinsen Ejland (Alluttoq), located 40 km southeast of Saqqaq, we infer wave runup heights of ca. 41–66 and 45–70 m, respectively, for the two tsunami events. These runup heights from prehistoric tsunamis are 1 to 2 orders of magnitude higher than the historic landslide-tsunami runup heights at Saqqaq which only reached an elevation of ca. 3 m in November 2000. While we found deposits from two tsunami events in the lake sediments, landforms from at least nine giga-scale landslides are present on the seafloor of Vaigat. We infer that these deposits probably represent the two most recent tsunamis identified in the Vaigat strait and that the older tsunamis must have happened between the last deglaciation and the oldest sediment in the lakes, i.e., between ca. 10.0 and 8.5 ka cal BP.

Two efficient numerical techniques for solutions of fractional shallow water equation

In this paper, the nonlinear shallow water equation appears in the mathematical modeling of tsunami wave propagation along the coastline of an ocean is solved numerically. The model investigates fractional derivatives and is presented through a system of nonlinear partial differential equations. The variational iteration method (VIM) and the residual power series method (RPSM) have been applied to the fractional system of equations for different parameters. In addition, tsunami wave velocity and run-up height with respect to coast slope and sea depth are analyzed for different time and order in detail. A detailed error analysis is presented for tsunami velocity and tsunami wave propagation. The results obtained are compared to other existing results to show the efficiency and reliability of the proposed methods.

Groupiness effect on irregular wave train propagation and impact on cylinder

A wave flume based on solving the Reynolds-averaged Navier-Stokes equation is modelled to simulate the irregular wave group interacting with a cylinder. The irregular wave groups are generated based on the wave envelope spectrum and the improved JONSWAP spectrum. The wave-making boundary and the momentum source term for wave-making and wave dissipation are developed based on the irregular wave theory. To suppress excessive growth of turbulent viscosity, a modified formula for turbulent viscosity is implemented in the shear stress transport turbulence model. Several sets of irregular waves with different groupiness factors are simulated. The effects of groupiness on the wave parameters, wave run-up height and wave force on the cylinder are investigated. The results show that the wave parameters increase as the groupiness increase. The group height factor has a larger influence on the significant wave height than the group length factor. The group length factor mainly influences the average wave period and average wavelength. When the average wavelength is larger than the diameter of the cylinder, the increase in wave group length results in a decrease in wave run-up height and wave force on the cylinder.

Stereo vision-based measurement of wave evolution around square column in laboratory

The spatial-temporal measurement of complex wave evolution is significant in studying wave-structure interactions. Current methods, such as that using wave probes, have shown limitations in measuring the wave evolution around structures in laboratories. In this study, an improved stereo imaging method is proposed for measuring the wave evolution around a fixed structure. Regular wave tests were conducted on a fixed surface-piercing square column in a wave flume to validate the reliability and accuracy of the proposed method. A flexible marker-net made of foam particles was arranged around the column to provide Lambertian features for the water surface. Two synchronized stereo imaging systems covered all the surrounding areas of the column and provided stereo pair sequences for wave evolution. Subsequently, image segmentation techniques were used to mask the low-confidence disparities in stereo matching, and finally, three-dimensional (3D) wave surfaces were reconstructed in the time sequence. The time histories of the wave elevations at particular locations were extracted and agreed well with the measurements of wave probes with an average bias of 2.4 %. Subsequently, the reconstructed 3D wave field was sliced, exhibiting the instantaneous profiles that agreed with the measurements of wave probes. Moreover, the wave run-up height ratios were consistent with those of a previous study, thereby verifying the method's accuracy from the perspective of spatial evolution. The results demonstrated that the proposed method was capable of precisely measuring the spatial-temporal evolution of the wave field around the square column and displayed potential for application in more studies on wave-structure interactions.

INVESTIGATION OF DIRECTIONAL SPREADING EFFECT ON WAVE RUN-UP USING SWASH

In order to keep optimal safety of coastal lines, it is necessary to maintain an appropriate crest level of coastal dikes. This is designed based on wave run-up height and/or wave overtopping discharge. Therefore, it is important to estimate wave run-up and overtopping as accurate as possible. However, the influence of directional spreading on wave run-up and overtopping has not been fully understood yet. In this study, non-hydrostatic model SWASH (Zijlema et al., 2011) is used. First, we implemented a wave run-up model in SWASH in 2DV (flume like) and 3D (basin like). Then wave run-up are simulated for some different cases and compared to the existing empirical wave run-up formulas in literature (e.g. Holman, 1986 and Mase, 1989).

Physical Model Experiment for Estimating Wave Overtopping on a Vertical Seawall under Regular Wave Conditions for On-Site Measurements

Apart from implementing hardware solutions like raising the crest freeboard of coastal structures to efficiently counter wave-overtopping, there is a simultaneous requirement for software-driven disaster mitigation strategies. These tactics involve the swift and accurate dissemination of wave-overtopping information to the inland regions of coastal zones, enabling the regulation of evacuation procedures and movement. In this study, a method was proposed to estimate wave-overtopping by utilizing the temporal variation of wave heights exceeding the structure’s crown level, with the aim of developing an on-site wave measurement system for providing wave-overtopping information in the field. Laboratory model experiments were conducted on vertical seawall structures to measure wave-overtopping volumes and wave runup heights under different wave conditions and structural freeboard variations. By assuming that the velocity of water inundation on the top of the structure during wave-overtopping events is equivalent to the long-wave velocity, an overtopping discharge coefficient was introduced. This coefficient was utilized to estimate the rate of wave-overtopping based on the temporal changes in wave runup heights measured at the top of the structure. Upon reasonably calculating the overtopping discharge coefficient, it was verified that the estimation of wave-overtopping could be achieved solely based on the wave runup heights.

A Study on the Characteristics of Beach Profile Evolution According to the Particle Size Variation of Beach Nourishment

This study investigated the beach nourishment effect and topographical changes when using nourishment sand with relatively large particle diameters to perform beach nourishment on a beach subject to erosion. A physical model test was conducted in a 2D wave flume with an installed wind tunnel. The experiment examined the sediment transport mechanism under conditions with wind and waves. Although applying nourishment sand with large particle diameters attenuated sediment transport, the increase in particle diameter was not always proportional to the reduction in topographical changes. Increasing the particle diameter of the nourishment sand increased the friction force between particles, resulting in large-scale erosion and accretion around the coastline, and this trend increased with winds. Also, with wind, the wave run-up height increased, the undertow became stronger, and large-scale scouring occurred at the boundary between the nourishment sand and the existing beach. Increasing the particle diameter of the nourishment sand played a role in reducing the run-up phenomenon (d50: 1.0 mm with 24–50%, d50: 5.0 mm with 59–83%), and the range of particles moved by winds also decreased (d50: 1.0 mm with 10–38%, d50: 5.0 mm with 5–37%).

Influence of Excavation Pits on the Wave Hydrodynamics of Fringing Reefs under Regular Waves

Dredging materials from reef flats have become an important source of sand and aggregates for meeting the infrastructure needs of coral-lined shores in subtropical and tropical regions, especially for low-lying atoll islands. Dredging at the reef flats can generate artificial excavation pits, which not only have profound influences on coral ecological stability but also deeply affect the hydrodynamic characteristics of coral reefs. To deepen the understanding of the influence of excavation on the wave hydrodynamics of fringing reefs, the wave propagation, wave transformation, wave setup, and wave runup processes of regular waves on fringing reefs with artificial pits have been systematically analyzed using a non-hydrostatic numerical wave solver (NHWAVE). The effects of some significant factors have been carefully investigated. According to the study findings, the existence of artificial pits can result in a slight decrease in the wave height around the artificial pit. The time-mean maximum of wave runup height at the backreef slope can be reduced to some extent when the artificial pit is present. When placed close to the reef edge, the artificial pit can have noticeable effects on the hydrodynamic characteristics of fringing reefs, particularly the wave setup along the reef flat. It is hoped that the study findings can provide further reference for evaluation of the influences of artificial pits on the wave hydrodynamics of fringing reefs.

Numerical modelling of wave run-up heights and loads on multi-degree-of-freedom buoy wave energy converters

With the development of wave energy converters (WECs), multi-degree-of-freedom (multi-DOF) buoy has become popular. The effect of nonlinear phenomena, such as wave run-up and wave impact, on an oscillating buoy WEC, may decrease its efficiency and even lead to overturning, plastic deformation, and fatigue failure. This study used a Fortran code for the custom development of Flow-3D software to apply independent power take-off (PTO) damping to each DOF. A hydrodynamic simulation model of the interaction between a wave and cylindrical buoy under six types of motions was developed and verified through model tests of the motion response of the buoy and wave run-up on it. Wave run-up heights and maximum wave loads on buoys with different motions and PTO combinations were investigated and compared. The numerical results show that coupled motion can lead to a less intense wave field distribution than a single motion and reduce the risk of overtopping. In addition, the bottom pressure of the buoy for the pitch–surge motion increased by a maximum of 101.6 % compared to the initial pressure. For independent linear PTO damping, heave damping has the most significant influence on the maximum wave load on the coupled motion buoys, followed by surge damping, while pitch damping has no significant effect. The results of this study can guide the designing of safe and reliable multi-DOF buoy WECs.

Using 17 years of beach/dune profile monitoring to characterize morphological dynamics related to significant extreme water level events in North Brittany (France)

Long-term in situ monitoring of beach morphology is crucial for understanding the physical processes of coastal changes and defining the strategies of sustainable coastal management. Monthly surveys based on the beach/dune profile measurements started in July 2004 along six transects distributed along the Vougot beach (North Brittany). The analysis of these data from 2004 to 2021 shows that the eastern part of the beach has experienced chronic erosion during the 17-year period. This erosion has led to a lowering of the beach profile by about −1 to −1.5 m, and has resulted in the removal of beach sand such that waves now impact the underlying Holocene peat and Pleistocene silts or pebbles during most of the year. Conversely, the western part of the beach has accreted. Vougot beach is thus experiencing a rotation phenomenon characterized by a longshore sediment flux from the east to the west. The multidecadal evolution of the beach/dune system is punctuated by events causing significant retreat of the dune, especially when storm waves are combined with high spring tide levels. The event causing the most significant morphological changes was associated with extreme water levels (EWL) up to 9.6 m (i.e., Anne storm in February 2014), causing 14.5 m3 l.m−1 of dune sediment loss. The analysis of 17 years of hydrodynamic conditions (waves and water levels) indicates an increase in the wave runup height (+65 %) and EWL (+17 %). Calculation of the water level that exceeds the dune toe position (Δzexceedance) helps to further quantify the impacts of storm events on dune volume changes. The Anne storm had an EWL with a return period of approximately 13 years, but when combined with the dune toe position, showed the largest dune toe exceedance value (3.0 m), corresponding to a return period of approximately 21 years. Lastly, the events causing the most significant dune erosion during this 17-year study period have also caused shoreline erosion and/or landward barrier migration at many other sites in North Brittany, showing the broader scale impacts of observations at individual study sites.

Development of a typhoon wave overtopping prediction model based on an artificial neural network

In this study, an artificial neural network (ANN) model for the typhoon wave overtopping was developed using the database by a numerical wave flume simulation. The developed ANN model is effective for saving calculation time largely. The accuracy of the model is also approached to over 95% of the numerical simulation. This accuracy was evaluated by the correlation coefficient and the root mean square error with the target data of the numerical simulation and output of the ANN model. This model quickly produces the mean wave overtopping rate, maximum wave run-up height, maximum wave overtopping depth and velocity at the middle point in the coastal road without high-fidelity numerical model and high-computing resources. It means that the typhoon warning system including the ANN models is powerful and useful rather than only the monitoring warning system currently in use.

Coral reef structural complexity loss exposes coastlines to waves

Coral reefs offer natural coastal protection by attenuating incoming waves. Here we combine unique coral disturbance-recovery observations with hydrodynamic models to quantify how structural complexity dissipates incoming wave energy. We find that if the structural complexity of healthy coral reefs conditions is halved, extreme wave run-up heights that occur once in a 100-years will become 50 times more frequent, threatening reef-backed coastal communities with increased waves, erosion, and flooding.

Numerical investigation of effects of artificial excavation pit on transformation and runup processes of tsunami-like wave over fringing reef

In recent years, excavating materials from the reef flat gradually becomes the main source of sand and aggregate for the coral-lined coasts in tropical and subtropical regions, especially the low-laying atoll islands. These artificial excavation pits are bound to have significant impacts on the wave hydrodynamics over the fringing reefs. However, effects of the excavation pit on the hydrodynamic characteristics of tsunami-like wave over the fringing reef are few studied. To fill the knowledge gap of previous research, effects of artificial excavation pit on the transformation and runup processes of tsunami-like wave over the fringing reef have been systematically investigated in this study based on a high-resolution two-phase flow model. Effects of several main factors are carefully discussed. Research results indicate that the presence of excavation pit can have noticeable influences on the wave transformation and runup processes of tsunami-like wave over the fringing reef. Complex interactions between the breaking surge bore and the water body in the excavation pit can be observed. The complicated flow field in the pit can dissipate more wave energy and result in a lower maximum wave runup height. However, the local wave height near the pit in most situations can be amplified. It is hoped that the research findings can broaden the understandings on the wave hydrodynamics over the fringing reef with the artificial excavation pit.

Numerical Simulation on Reduced Runup Height of Solitary Wave by Fixed Submerged and Floating Rectangular Obstacles

The wave runup height is one of the most important parameters for affecting the design of coastal structures such as dikes, revetments, and breakwaters. In this study, SWASH (Zijlema et al., 2011), a non-hydrostatic pressure numerical model, was used to analyze the effect of reducing The wave runup height of solitary waves by submerged and floating rectangular obstacles. It was confirmed that the SWASH model reproduces the propagation, breaking, and runup of solitary waves quite well. In addition, it was confirmed that the wave deformation of the solitary wave by submerged and floating rectangular obstacles was well reproduced. Finally, we conducted an examination of the effect of reducing the runup height of submerged and floating rectangular obstacles. Reduced runup heights are calculated and the characteristics of runup height reduction according to the dimensions of the obstacle were analyzed. The energy attenuation effect of the floating obstacle is greater than the submerged obstacle, and it is shown to be more effective in reducing the runup height.