Wave Run-up Research Articles

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.

Three-dimensional shape optimization of a submerged body under wave diffraction

This study explores the use of shape optimization to reduce wave forces on a submerged floating body subjected to wave diffraction. To this end, gradient-based shape optimization is adopted, in which dimensionless wave excitation forces are the optimization objective. A shape parameterization method based on the Fourier-series expansion is developed that permits the representation of an arbitrary three-dimensional floating body. The discrete adjoint method is utilized to calculate the gradient of the objective function with respect to the shape parameters. Using three-dimensional shape optimization, taking the initial shape to be a hemisphere, a significant reduction in surge, heave, and pitch wave forces is achieved, with a maximum reduction of 48.40%, 68.43%, and 46.22%, respectively. Furthermore, optimization effectively suppresses wave run-up, with a maximum reduction of 15.62%. A comprehensive analysis of parameters is performed to reveal the effects of wave number, incident angle, and shape parameters on the final optimized shape and wave load characteristics. This study provides a solid guide to the optimization of floating offshore platforms and the development of innovative structural systems.

Study with Large Eddy Simulations of energy dissipation due to backwash flows in wave overtopping.

Renewable energy market growth is imperative to reach a sustainable society. This necessity demands improving existing methodologies to exploit green energy sources and explore new technologies. Wave energy is one of the sources with the larger offer in power available in the oceans to be harvested; however, the remoteness and extreme conditions of the best locations to harvest wave energy have made the development of wave energy converters expensive and less attractive than other green energy sources that operate on land. Overtopping wave energy converters (OWEC) operate on the shore, facilitating their construction and maintenance. They can be integrated into coastal defences, sharing the cost of construction and their environmental impact and creating new benefits from the coastal defence. The effectiveness of an OWEC relies strongly on their ability to capture wave-overtopping volumes. The geometry of the run-up ramp (slope and shape) plays an important role in the efficiency of an OWEC. An optimum geometry for each location and wave condition needs to be found to maximise the operation of any OWEC. The efficiency of these devices, quantified by the hydraulic efficiency, must be improved to make them an attractive solution for energy conversion. Three distinguishable processes occurred on the ramp of an OWEC; the wave collapse, run-up and run-down (backwash). The first two have attracted more attention from researchers, specially oriented to the design of coastal defences, but fewer studies have analysed the impact of the backwash on the energy losses during the collapse of the waves. When an incoming wave approaches the run-up ramp, it crashes against the backwash, composed of the water volume that didn't overtop the structure in the previous wave. These interactions increase turbulences and, therefore, energy dissipation, affecting the performance of an OWEC. This study analyses the hydrodynamics during the backwash flows' and incoming waves' interaction on sloped structures. A numerical code Hydro3D, based on Large Eddy Simulations, is used to conduct the present study. As a reference condition, a structure with a freeboard high enough to not allow wave overtopping is tested; in this case, all the water that run-up the slope runs down after the water tongue reaches its highest elevation. Structures with lower freeboards are tested to allow different wave overtopping levels and backwash flows. The impact of different backwash flow conditions on energy dissipation is then evaluated. The founding of this study allows us to verify if a reduction in the backwash flows can improve the efficiency of a OWEC.

IMPLICATIONS OF SECOND-ORDER WAVE GENERATION FOR USE IN WAVESTRUCUTRE RESPONSE EXPERIMENTS

Coastal communities and critical coastal assets are therefore increasingly reliant on engineered protection from wave-induced flooding. Dynamic wave force and wave run-up are among key design parameters of such protection. Present understanding of coastal wave-structure interactions and responses was gained through large databases of experimental data as well as numerical, and field measurements. It is well known that experimental data of wave-structure interaction are contaminated by second-order error waves at sub- and super-harmonic frequencies when first-order wave generation is used. The error waves arise from disparity between linear wave-maker signals and non-linear boundary conditions at the wave generator. Herein, we conduct a novel investigation by experiment of the implications of second-order wave generation for dynamic wave force and run-up on a vertical wall, in shallower depths than previously published (kd = 0.6 - 1.1). The implications of error waves on coastal responses is quantified through comparison of first-order generated (FOG) and secondorder generated (SOG) wave group experiments.

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).

WAVE TRANSFORMATION AND RUNUP VARIABILITY DUE TO WAVE PHASE UNCERTAINTY

Wave runup is a significant portion of total water levels, particularly during storms (Sallenger, 2000). This makes accurate prediction of wave runup paramount. Wave runup can be estimated using simplified empirical models (e.g. Stockdon et al 2006) or simulated using phase-resolved Bousinesq models (Shi et al 2007, Lynett et al 2002) or non-hydrostatic models (e.g. Zijlema et al 2011). These models typically have a variety of offshore boundary input options ranging from spectral to time series, with the most broadly used being spectral parameterizations (e.g. JONSWAP, TMA, etc.) or direct spectral input, both of which neglect phase information at the offshore boundary. Recent research has highlighted the importance of the offshore boundary condition and wave phase at modeling wave runup (e.g. Fiedler et al 2019, Rutten 2021). This work pays careful attention to the consequences of the bound infragravity (IG) wave and explores the influence that unknown phase information can have on predicted wave transformation and resultant wave runup in the context of field observations.

THE CONTRIBUTION OF WAVE RUNUP TO COASTAL FLOODING AT NORFOLK (VA, USA) DURING EXTREME EVENTS

Coastal flooding occurs when the total water level (TWL) elevation exceeds that of the natural (e.g. dune) or built (e.g. levee) coastal defense. Operational models that estimate the TWL typically consider the combined effect of mean sea level (MSL), high tide, and storm surge. However, the extent to which storm waves run up the beach or structure is often neglected, as either computationally demanding numerical or site-specific empirical models are required to accurately resolve the components of wave runup. These components include a time-averaged surface elevation at the shoreline (wave setup) and time-varying fluctuations about that mean (swash), which may be further divided into high-frequency (sea and swell, SS) and low-frequency (infragravity, IG) motions. Therefore, any prediction tool used to estimate wave runup must account for breaking waves, which drives wave setup and infragravity motions. While neglecting wave runup allows for rapid hazard assessment on a large scale, studies have shown that its exclusion can lead to a significant underestimation in the TWL (Serafin et al., 2017). In this study, we assess the contribution of the individual components of wave runup (wave setup, SS and IG wave motions) to the TWL at the Norfolk Naval Station and its surrounding region (VA, USA) — a mesotidal area characterized by a mild continental shelf and exposed to hurricanes and nor’easters.

HOW BEACH STATE INFLUENCES WAVE RUNUP ON A PERCHED BEACH IN SOUTHWESTERN AUSTRALIA

Approximately 20 to 30 percent of the world’s coastlines are fronted by shallowly buried or outcropping shore platforms overlain by perched beaches (Kirk, 1977; Marshall and Stephenson, 2011; Trenhaile, 2002). Seasonal erosion of perched sediment can shift the beach state from ‘accreted’ to ‘exposed’ (Gallop et al., 2011), and the effect this has on wave-induced flood risk (known as wave runup) is unknown. As sea levels rise and storm severity increases, understanding how beach state influences wave runup is crucial for minimising coastal hazard risk and managing perched beach coastlines. In this work, idealised numerical modelling and field observations along a perched beach in southwestern Australia were used to quantify the influence of beach state on wave runup, setup, and swash processes.

MULTI-SCALE WAVE MODELLING; FIELD VALIDATION IN FAXE BAY, DENMARK

Access to local nearshore wave climate conditions on a detailed spatial scale is important for many coastal engineering practices. These include assessing the flood risk of coastal infrastructure, designing coastal protection measures, and estimating sediment transport processes and wave run-up. The present study displays a multi-scale wave modelling approach using the numerical wave model SWAN (Booij et al., 1999) together with field data applied in the southern Baltic Sea. The main objective of the study was to investigate the possibility of employing a single wave model for seamless simulations over several scales in time and space, from offshore to nearshore, including the effects of grid size and resolution. Validation with extensive field data was a crucial part of the study.

FUTURE FLOODING OF THE VOLTA DELTA CAUSED BY SEA LEVEL RISE AND LAND SUBSIDENCE

The Volta delta(Ghana, West Africa) is increasingly impacted by sea level rise (SLR). SLR makes the Volta delta mostly vulnerable to flooding, salinization of water resources and agriculture fields, and permanent loss of lands. This would potentially threaten and present a growing risk to its population, infrastructure and economy, and even worsen due to land subsidence (LS). Relative sea level rise (RSLR) in this study is the rate of LS with respect to SLR. It is thus very important to precisely quantify LS rates together with SLR as well as planning and assessment of countermeasures. This study is in two parts, The first study presents and discusses recent LS rates in the Volta delta derived from satellite-based SAR-Interferometry and their impact on relative SLR. The second study, also assesses major hydrodynamic parameters (Wave runup, Sea Level Anomaly,tide and atmospheric conditions) that play a role in extreme coastal flooding events.

EXPERIMENTAL ANALYSIS OF HYBRID SOLUTIONS FOR COASTAL PROTECTION

Among the newest strategies are nature-based solutions based on coastal ecosystems (Spalding et al., 2014; Jongman 2018). Such solutions have several co-benefits, such as habitat creation, increased water quality or carbon sequestration. However, these solutions may not be effective on their own in high-risk areas or in areas where there is not enough space for their implementation. In these cases, the union of conventional engineering with these nature-based solutions, the so-called hybrid solutions, can represent an optimal solution that provides the necessary risk reduction while reporting the cobenefits associated with natural solutions (Sutton-Grier et al., 2015; Vuik et al., 2016). This makes hybrid solutions a highly attractive option in which there is a growing interest. However, their relatively novel character, the few real cases implemented and the need for a strong integration of knowledge linking different disciplines pose a series of gaps in knowledge. To this end, an experimental campaign is proposed to study different typologies of hybrid solutions. The interaction between the ecosystem and the hard structure is studied to better understand the coastal protection service provided by the joint solution. To compare the performance of the different hybrid solutions, wave run-up over the rigid structure is analyzed and it is compared to the run-up obtained for the traditional rigid solution.

ASSESMENT OF WAVE OVERTOPPING ON REEF-FRONTED SHORES

Overtopping has been widely studied to design coastal structures, and it is also an important parameter for coastal management in order to evaluate the protection by natural coastal systems against inundation. Most formulations for open coasts have estimated overtopping using the wave runup (R2 percent), the beach slope and the truncated point, with empirical coefficients to account for further details (e.g. EurOtop, 2018). However, for beaches that are naturally protected by fringing reefs, the knowledge of overtopping is limited, and reliable analytical formulations have not been developed. The aim of this research is to evaluate the previous overtopping model and scaling laws and suggest one model applicable to reef-fronted shores.

WAVE ATTENUATION OF SALTMARSH VEGETATION UNDER STORM CONDITIONS

Nature-based solutions (NbS) for coastal protection has recently gained increased attention worldwide as a sustainable, economical and eco-friendly alternative to conventional grey structures, particularly under the threat of climate change (Temmerman et al. 2013). Wave energy dissipation by vegetation can be parameterized by the total horizontal force acting on the plant; expressed using a Morison-type equation considering only the form drag component (Dalrymple et al. 1984). Modelling wave-vegetation interaction is challenging in a laboratory environment (Lara et al. 2016) and it is difficult to accomplish a realistic representation of a plant’s biomechanical behavior and geometry using plant mimics or surrogates. Few studies have modelled real saltmarsh vegetation in large scale laboratory facilities (Moller et al. 2014; Maza et al. 2015) and quantified wave attenuation, particularly for engineered living shorelines (Maryland DoE, 2013). Further research is needed, particularly in the Canadian context, to investigate the capacity of different saltmarsh species to effectively attenuate waves and wave runup under storm conditions, to examine the plant’s drag coefficient and to bridge the gap to develop technical design specifications for the detailed design of living shorelines.

FIELD STUDY FOR WIND-BLOWN SAND ON THE SWASH ZONE

Niigata West Coast faces the Sea of Japan and Sado Island is located approximately 45 km to the west from there (Fig.1). This coast has suffered severe erosion since the early 1950s. Hiyoriyamahama beach where is a part of the Coast is a highly erosive beach. For the protection of the beach erosion, the combined shore protection system with the jetty, submerged wide breakwater and beach nourishment have been constructed at the beach. There, strong winds from NW to WNW blow in the winter season and nourished sand has been blown off from the beach. For the prevention of blown off nourished sands from the beach, an attempt to develop an integrate system for controlling the wind-blown sand combined with sand fences, a green belt (an artificial low dune) and a vacancy space (road) has been made. To examine the function of the integrate system under development, extensive field surveys for beach topographical changes, wave runup on the swash zone, wind at the site, waves have been conducted. The purpose of this paper is to describe the field measurement results.

BERM MIGRATION UNDER SCALED STORM EVENTS

Berms are one of the natural barriers protecting beaches from wave action and are the first intermittently exposed coastal feature to experience hydrodynamic forcing. Berms erode when storm activity mobilizes sediment offshore or carries it onshore through overwash. However, berm response under varied storm conditions requires further study. Pore water pressure response has been shown to potentially impact beach erosion (Stark, 2022). The infiltration from wave runup followed by exfiltration from rundown destabilize the sediment bed resulting in particle motion. Wave runup increases bed shear stress (Sumer, 2011), and horizontal pressure gradients have been shown to mobilize sediment in the surf zone (e.g. Anderson, 2017). Erosion occurs from numerous physical processes acting together to mobilize the sediment. This study aims to identify these physical processes and berm response for variety of scaled storm sequences.

FIELD MEASUREMENTS OF WAVE INTERACTIONS WITH A DIKE ON A SHALLOW FORESHORE USING AN “ARTIFICIAL DIKE” CONCEPT

Low-lying countries typically have mildly-sloping beaches as part of their coastal defence system. Many countries in north-western Europe have coastal urban areas that rely on this type of defence system, which consists of a lowcrested impermeable sea dike with a relatively short promenade, and a long (nourished) beach in front that acts as a very/extremely shallow foreshore as defined by Hofland (2017). Along the cross-section of this hybrid beach-dike coastal defence system, storm waves are forced to undergo many transformation processes before they finally overtop the dike. These hydrodynamic processes include shoaling, sea and swell wave energy transfer to sub- and superharmonics via nonlinear wavewave interactions, wave dissipation by breaking and bottom friction, reflection against the dike, wave run-up and overtopping on the dike, bore impact on a wall or building, and finally reflection back towards the sea interacting with incoming bores on the promenade. Field measurements of all these processes at the same time are very challenging but necessary since these suffer from neither scale nor model effects. Field data are therefore crucial to evaluate design methodologies, which rely on physical and numerical modelling. This paper presents the field setup and the design features of the innovative artificial dike, unique in the world.

Nonlinear Effects and Run-up of Coastal Waves Generated by Billiards with Semi-rigid Walls in the Framework of Shallow Water Theory

Nonlinear Effects and Run-up of Coastal Waves Generated by Billiards with Semi-rigid Walls in the Framework of Shallow Water Theory

REVISITING WAVE PROPAGATION UNDER AIR FLOW IN COASTAL AREAS

The interaction between ocean waves and winds can be separated into two main analyses. A first interaction considers the wind as the primary wave generator. The mechanism through which wind exerts stresses to the water surface that combined with the gravity forces produce the surface oscillatory flow known as waves, is relatively well documented theoretically (Blennerhassett 1980), experimentally (Plate et al. 1969) and numerically (Liu et al. 2016). On the other hand, as waves travel to the coast, winds stop being the generating force and turn into an energy source travelling along with the waves. In places close to the shore, winds can be directed with or against the wave propagation. It is straightforward that wave properties close to the shore are modified under different wind conditions (Xie 2017). Numerical and experimental studies on wave-wind interaction near the coast and in presence of obstacles exist but are still scarce (Medina 2001). The present research is an experimental study of the perturbation produced by an air flow over waves in shallow waters and interacting with sloped obstacles. Well-known phenomena such as wave braking, steepening and run-up are revisited under wave-wind conditions.

THE INFLUENCE OF SUBMERGED COASTAL STRUCTURES ON NEARSHORE HYDRODYNAMICS

Submerged coastal structures (e.g., submerged breakwaters and natural and artificial reefs) are common in nearshore waters globally. By locally reducing water depths from the surrounding bathymetry, they modify the incident wave field, mean currents, runup and sediment transport around them. Although submerged structures are generally assumed to promote coastal protection by dissipating waves offshore and creating sheltered conditions in their lee, their interaction with waves can result in wave-driven circulation patterns that may either promote shoreline accretion or erosion (Ranasinghe et al., 2006). A meta-analysis of the coastal changes resulting from the construction of submerged breakwaters found that, contrary to expectation, in the majority of the cases erosion occurred in their lee (Ranasinghe and Turner, 2006). Therefore, a detailed understanding of the wave structure interactions and resulting hydrodynamics is paramount to predict coastal changes in their lee. Here we explore the detailed wave-driven hydrodynamics in the lee of submerged structures using phase-resolved modelling.

OBSERVATION AND NUMERICAL MODELING OF A DUNE OVERWASH AND BREACHING EVENT

Sea level rise will significantly increase the need for building and upgrading coastal protection such as artificial coastal dunes or berms (Wong et al., 2014). Human constructed dunes are frequently deployed to limit wave runup and overtopping and mitigate damage from flooding events (e.g., Gallien et al., 2015). Although dune erosion modeling and validation on storm surge dominated beaches is common in the literature, only limited work considers energetic long period swell conditions typical of coastal California. In this study three morphological models are used to simulate dune erosion response to long period swell and compared to high resolution in-situ hydromorphological field observations.