Wave Run-up Research Articles

OBSERVATIONS FROM A CONTROLLED DUNE EROSION EXPERIMENT UNDER VARIABLE WATER LEVELS, WAVES, AND INTERNAL DUNE MOISTURE CONTENT

Dune erosion due to storms is primarily predicted by the use of empirical relationships, for example, when the duneface slope exceeds a certain threshold sand is eroded (SBeach, XBeach); or as a function of wave impact (Larson et al., 2004). However, geotechnical properties also play a role in dune scarp formation. Dry sand is relatively unstable, but as water is added, the tensile strength increases, enabling a vertical duneface to form and reduce slumping. The strength and stability of the sand matrix increases up to 10-15 percent with increasing water content, and then decreases as the sand matrix becomes saturated and more easily eroded. Hence, it is somewhat surprising that the importance of water infiltration into the dune sand matrix and resulting porewater content have received relatively limited attention within the coastal engineering literature to-date. This paper presents new results from a series of controlled laboratory experiments to observe moisture content and pore pressures within an eroding dune, to better understand the importance of wave run-up infiltration to dune erosion under wave attack.

MODELING COASTAL WATER TABLE FLUCTUATIONS USING PFLOTRAN

Coastal aquifers are highly dynamic groundwater systems. Sea level rise will cause a rise in coastal groundwater tables resulting in increased risk of shallow or emergent groundwater (Befus et al., 2020). Marine water level fluctuations cause the beach groundwater table to oscillate over a relatively large range. Understanding these oscillations is crucial, as shallow (i.e., high) water tables may impact subsurface infrastructure, mobilize sediment, and increase liquefaction risks. Although the impacts of tides and wave setup on coastal water tables have been studied (e.g., Nielsen, 1990; Housego et al, 2021), the cumulative impacts of wave runup, partially saturated flow, complex beach topography, and dual tidal forcing for bay-backed regions have not been explored. This work numerically models beach water table fluctuations which are compared to in-situ swash and beach groundwater observations at Cardiff State Beach in Encinitas, CA.

MONITORING OF A DYNAMIC REVETMENT DURING A SPRING TIDAL CYCLE IN NORTH COVE, WASHINGTON STATE, USA

A dynamic revetment is a cobble-gravel berm constructed around the high tide wave runup limit. These structures mimic composite beaches, which consist of a lower foreshore of sand and a backshore berm constructed of gravel or cobbles, which stabilizes the upper beach and provides overtopping protection to the hinterland. Dynamic revetments contrast with static coastal defense structures as they are “dynamic” and are expected to reshape under wave attack. The idea of a dynamic structure made of smaller material than a classic riprap type of revetment is not new, and previous laboratory and field research has investigated the use of dynamic revetments for coastal protection (Allan et al., 2016). However, applications of such a structure remain sporadic and often differ to each other in terms of their design and aim. Furthermore, few existing dynamic revetments have been monitored to evaluate their function, and therefore, the way they behave at the particle and global scale remains poorly understood. In this study, 2D Lidar, GPS topography, particle tracking, and sub-surface particle composition data were collected on the dynamic revetment at North Cove, Washington State, USA, during a spring tidal cycle. Together they enabled investigation of the revetment dynamics and evolution in response to waves and water levels. In addition, this monitoring is proposed as a suitable protocol for short and long-term monitoring of dynamic revetments.

BEACH GROUNDWATER IMPACTS ON WAVE OVERTOPPING FLOODING

Coastal flooding is a growing socioeconomic and humanitarian hazard (e.g., Nicholls, 2010). Increased beach groundwater levels may inundate low-lying areas and simultaneously propagate swash impacts onto higher beach and backshore elevations. Generally, coastal flood modeling and risk assessment characterize only surface flows, neglecting beach groundwater and swash zone processes such as infiltration and porous media flow. Numerous studies have considered the effects of swash on groundwater (e.g., Gourlay, 1992). Infiltration leads to reduced wave runup (Pintado-Patino et al., 2015) and is promoted by low beach groundwater levels (Bakhtyar et al., 2011), suggesting that beach groundwater plays a critical role in infiltration/exfiltration processes. Notably, the impacts of beach groundwater on swash flows and subsequent consequences on coastal flooding have not been explored. Coastal flooding from wave overtopping is expected to occur around the maximum tide. However, recent field observations suggest maximum overtopping lags behind high tide and is in phase with maximum groundwater levels. In this study, a turbulence and depth resolving numerical model is developed to examine the interaction between beach groundwater and wave overtopping processes.

PREDICTION OF TOPOGRAPHIC CHANGES ON ENSHU-NADA COAST CONSIDERING EFFECT OF BOTH WAVES AND WINDBLOWN SAND

The morphology of sand dunes formed on the Maisaka and Hamamatsu coasts facing the Enshu-nada Sea was investigated by field observation. The development of sand dunes was numerically predicted using a model predicting the effect of both waves and windblown sand. In the field observation, the development of sand dunes with a rhythmic shape similar to a sand spit was observed in the backshore area. It was found that pine trees died in the area with a narrow sand dune owing to wave run-up and the dispersion of salinity during storm wave conditions. In the numerical simulation, the formation of sand dunes was successfully reproduced under the condition that the predominant wind blew at a large angle relative to the direction normal to the shoreline.

SPATIAL VARIABILITY IN BEACH-FACE SLOPES FROM SATELLITE REMOTE SENSING

The beach face is the most seaward region of the dry beach. This region is the primary interface between land and ocean, and therefore has a great influence on coastal processes such as the exchange of sediment between land and sea or the reflection of wave energy at the shoreline. In particular, the slope of the beach-face, is an important parameter in coastal engineering to calculate the vertical and horizontal excursion of wave run-up (Stockdon et al., 2006). Yet, despite the importance of the beach-face slope parameter in many formulations used by coastal engineers, this quantity remains poorly mapped along the world’s sandy coastlines and the absence of large-scale datasets of beach-face slope is presently limiting our ability to deploy coastal inundation forecasting systems (O’Grady et al., 2019). This work describes a novel methodology to estimate beach-face slopes with satellite remote sensing and presents large-scale datasets of beach-face slopes along open-coast sandy coastlines around the Pacific Rim.

Mesoscale Shoreline Evolution on a Carbonate Sand Island: Anegada, British Virgin Islands

Anegada, the easternmost island of the Virgin Islands group (Caribbean Sea), is a low Pleistocene carbonate platform surrounded by Horseshoe Reef, the world’s third-largest fringing reef. The western part of the island consists of an extensive beachridge plain (>40 ridges). The sandy carbonate shoreline exists in three morphodynamic domains that exhibit distinctive behaviour over the 59-year study period (1953 to 2012). The northern shore is dominated by westerly longshore drift under fair-weather conditions and cross-shore sediment transport during high-energy events. Storm wave run-up and high nearshore sediment availability contribute to the construction of shore-parallel beachridges. The western end of the island is affected by refracted waves that drive strong erosion and sediment transport. This is reflected in a succession of alternating rapid shoreline recession and progradation phases over the study period. The south–central shoreline is exposed to low wave energy and is stable and colonised by mangroves. The fringing reef plays a dominant role in mesoscale shoreline morphodynamics, both as a sediment source and in wave energy dissipation. Quasi-stable points and embayments suggest a strong influence of the reef framework in controlling the shoreline’s morphology and position. Sediment transfer from the reef to the shoreline appears to take place via shore-oblique, linear sediment transport pathways that develop across the lagoon in response to the modification of incoming waves. Cannibalisation of the shoreline sediment over the past 50 years is leading to straightening of the shoreline planform. This is counter to the long-term (Holocene) development of beachridges and suggests a change from a strongly positive to negative sediment budget.

NATIONAL ASSESSMENT OF HURRICANE-INDUCED COASTAL EROSION HAZARDS IN PUERTO RICO

Storms are one of the main causes of coastal erosion, causing substantial property and infrastructure losses in coastal communities. Coastal erosion is particularly damaging in underrepresented communities that are unable to meet building and zoning regulations due to limited resources [Lam, 2014]. The United States Geological Survey (USGS) has developed a probabilistic assessment of hurricane-induced coastal erosion for sandy coastlines along the eastern United States and the Gulf of Mexico. However, the current USGS product incorporates an empirical equation with inputs of beach slope and deep-water wave height and period [Stockdon, 2006] to predict the wave runup. Though this is appropriate for open coast sandy beaches, it is not valid for the rocky and reef lined coasts of Puerto Rico due to their complex bathymetries, steep slopes, and large bottom roughness. To expand this tool to Puerto Rico, the USGS has created 1-dimensional XBeach [Roelvink, 2009] models around the island.

A Numerical Study of Dam‐Break Driven Swash and Beach Groundwater Interactions

AbstractThe dynamic interaction between swash and beach groundwater is fundamental to understanding wave runup and sediment transport processes. A numerical model that simultaneously resolves free surface and porous media flow for a variably saturated subsurface is presented. The novel numerical model, SedOlaFlow, is developed by merging the existing two‐phase, Eulerian sediment transport model, SedWaveFoam, with the surface wave solver, olaFlow. SedOlaFlow is validated with large wave flume surface and subsurface data for dam‐break driven swash over permeable gravel and sand beaches. Sediment size significantly impacts the swash‐groundwater relationship through infiltration/exfiltration and subsurface processes which modulate runup. Model results demonstrate that vertical infiltration into the upper unsaturated beach leads to a delayed groundwater table response to swash in the sand beach. Pressure fluctuations in the sand beach are not directly indicative of the swash depth or groundwater table and exfiltration may occur even when the swash depth is non‐zero. Groundwater circulation induced by a single swash event is non‐uniform and highly dynamic in the variably saturated vadose zone. Elevated ambient groundwater levels generally increase swash extent and duration. These findings establish the existence of a bi‐directional relationship between swash and groundwater flows and have significant implications on the effects of sea level rise on coastal flooding.

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.

Studi Potensi Tsunami Bali Utara Menggunakan Metode Numerik


 
 
 
 Bali Island is one of the most tsunami-prone areas in Indonesia. Two tectonic tsunami sources flank Bali Island: The Megathurst subduction zone in the south and the Back Arc Thurst subduction zone in the north. This study aimed to add information about the tsunami arrival time and the maximum height of the tsunami waves that hit the coast using COMCOT software as a disaster mitigation measure. Five scenarios were used in this study with the differences in the magnitude of tsunami-generating earthquakes. Results showed that the fastest affected shoreline by the tsunami in scenarios 1, 2, and 3 is the Tejakula Sub District shoreline, with a period of 5 minutes 41 seconds to 3 minutes 43 seconds. In scenarios 4 and 5, it was found on the Sawan Sub District shoreline for 2 minutes, 51 seconds to 56 seconds. The maximum run-up of tsunami waves that hit the shoreline in scenarios 1, 2, 3, and 4 are on the Kubu Sub District shoreline with run-up heights of 0.0095 m, 0.47 m, 1.5 m, and 3 m. In scenario 5, the highest run-up is on the Banjar Sub District shoreline, with a 67.6 m run-up height. Based on the results of this study, it can be concluded that the magnitude of the tsunami-generating earthquake greatly influences the travel time and run-up height of the tsunami waves. The greater the magnitude of the tsunami-generating earthquake, the faster the travel time of the tsunami waves and the higher the run-up height.
 
 
 

The Reason for the Rise in Critical Shear Stress on Sloping Beds

In sediment mechanics, the conditions for the onset of sediment movement are of particular importance. However, despite decades of research, questions remain unanswered. Thus, physical logic suggests that sediments move more easily on beds inclined in the direction of flow than on horizontal beds and that transport rates are correspondingly increased. However, numerous studies have shown that sediments require increased rather than decreased shear stress to move on sloping beds and that transport rates are lower instead of increased. Since an early publication on this issue by Ashida and Michiue in 1973, many possible effects have been suggested for this apparent contradiction. The literature almost consistently concludes that high relative roughness (d/h), i.e., low water cover (h/d), is mainly responsible for this contradictory effect. This is true for current-induced sediment transport and for the initiation of debris flow. In this paper, an analytical solution for the effect of small water coverage on the transport process is developed. Effects of low coverage also occur on beaches during wave runup and runoff and thus control the formation of steep or less steep beaches. The present paper shows that the effect of turbulence damping occurring under low water coverage plays a decisive role here.

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%).

Wave scattering by porous cylinders with inner columns near a vertical wall

This paper studies wave scattering by multiple dual porous circular cylinders in front of a vertical wall. Each cylinder is composed of an outer partially perforated cylindrical shell and an inner impermeable column, and a circular wave-absorbing chamber is formed by the shell and column. An analytical solution to the hydrodynamic problem is developed in the context of potential flow theory. In the solving procedure, the hydrodynamic problem is transformed into an equivalent problem in an open water domain by using the image principle. The whole fluid domain in the equivalent problem is divided into multiple regions, and the velocity potential of the fluid motion in each region is expressed as the Fourier–Bessel series. The effect of the perforated shell on wave motion is considered through a pressure loss condition. The unknown coefficients in the velocity potential are determined by the transmission conditions on the boundaries between adjacent regions. The wave force, wave run-up on the porous cylinders, and the surface elevation near the cylinders are calculated. The analytical results are consistent with published results in several limiting cases. Typical cases are presented to clarify the characteristics of the wave force and wave run-up on the cylinders and discuss the effects of the wall and hydrodynamic interference on the hydrodynamic quantities. Moreover, several feasible applications of dual porous cylinders are discussed by visualizing the distribution of wave amplitude near the structures, and some valuable results are given.

Study on hydrodynamic characteristics of a hybrid wind-wave energy system combing a composite bucket foundation and wave energy converter

In this paper, a new type of combined wind-wave system is proposed, that is, composite bucket foundation-oscillating buoy (CBF-OB) combined device. A three-dimensional numerical wave flume is established by using the renormalization group k–ε model. The hydrodynamic characteristics around the wave and the combined power generation device are studied. The relationship between wave parameters and wave run-up and wave pressure is analyzed. The absorption efficiency performance of the combined power generation device is evaluated. The results show that in the combined power generation system, the wave run-up and wave pressure at 0°–135° around the CBF are smaller than those in the presence of only CBF, but near 180° the ones are larger than those in the presence of only CBF. In the rear side of the combined power generation system, the smaller the scattering parameters, the more obvious the phenomenon of the second wave peak, and the stronger the nonlinearity of the wave and CBF-OB combined power generation system. The proposed CBF-OB combined power generation device can significantly improve the absorption efficiency of the buoy, which can be increased by about 1.5–4.0 times compared with the absorption efficiency under the action of only the buoy alone. There is an optimal power takeoff parameter, that is, when the damping parameter is 500 N·s/m, to maximize the absorption efficiency of the combined power generation device.

Experimental hydrodynamic assessment of a cylindrical-type floating solar system exposed to waves

In this paper, an experimental investigation on the wave loads and structural motions of two semi-fixed semi-immersed horizontal cylinders type rafts in the free surface zone is conducted. The physical models are tested at the 1:4.5 scale and exposed to a range of regular and irregular waves in a wave flume at Queen's University Belfast. The physical models and experimental setup are discussed alongside an investigation of the hydrodynamic phenomena, surge forces, and dynamic responses that each structure exhibits in the coastal wave climates. Furthermore, an investigation into the wave attenuation by both models is carried out. The results show that the surge forces have a positive correlation with wave steepness for both models. Hydrodynamic phenomena such as wave runup and overtopping, radiative damping and reflected waves, constructive interference, diffraction and flow separation were identified during the experiments. A negative mean heave displacement is observed during the monochromatic sea states which could result in impact loading and submergence of the superstructure components and photovoltaic panels at full-scale. The results presented in this paper may be used to calibrate and verify numerical models that calculate the global responses and hydrodynamic forces. It may also benefit the design processes of geometrically similar floating solar technologies by providing data on surge loads, motion responses and hydrodynamic observations.

Statistical Analysis of the Wave Runup at Walls in a Changing Climate by Means of Image Clustering

This contribution builds on an existing methodology of image clustering analysis, conceived for modelling the wave overtopping at dikes from video records of laboratory experiments. It presents new procedures and algorithms developed to extend this methodology to the representation of the wave runup at crown walls on top of smooth berms. The upgraded methodology overcomes the perspective distortion of the native images and deals with the unsteady, turbulent and bi-phase flow dynamics characterizing the wave impacts at the walls. It accurately reconstructs the free surface along the whole structure profile and allows for a statistical analysis of the wave runup in the time and spatial domain. The effects of different structural configurations are investigated to provide key information for the design of coastal defences. In particular, the effects of increased sea levels in climate change scenarios are analysed. Innovative results, such as profiling of the envelopes of the runup along the wall cross and front sections, and the evidencing of 3D effects on the runup are presented. The extreme runup is estimated for the definition of the design conditions, while the envelopes of the average and minimum runup heights are calculated to assess the normal exercise conditions of existing structures.

Multi-scale calibration of a non-hydrostatic model for wave runup simulation

Modeling wave runup on beaches and structures is an important step toward accurate coastal flood prediction. Depth-averaged non-hydrostatic models such as XBNH (XBeach Non-Hydrostatic) are computationally cost-effective yet accurate tools to numerically simulate random wave runup. XBNH includes a number of calibration parameters, which are determined on a case-study basis. This study aims to investigate the range of XBNH input parameters that results in accurate predictions regardless of the application scale, benefiting future applications of XBNH that lack the measurements needed for model calibration. The study performs calibration and sensitivity analysis to investigate the model response to the input parameters for applications with different spatial scales, including small- and large-scale laboratory wave runup experiments and a real-scale field experiment. A Grid search method is utilized to perform a multi-scale calibration of the input parameters used in the parametrization of the wave breaking process in XBNH. The effect of parameters in the JONSWAP spectrum used to generate the offshore boundary conditions is investigated. Results show that using a single combination of calibrated input parameters, the model is able to capture random wave runup on beach, beach-dune, and beach-seawall systems with various spatial scales. Moreover, wave spectrum parameters can highly influence the model performance, and calibration of these parameters makes the model more robust to replicate the actual water surface fluctuations.

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.

Inverse problem for the nonlinear long wave runup on a plane sloping beach

We put forward a simple but effective explicit method of recovering initial data for the nonlinear shallow water system from the reading at the shoreline. We then apply our method to the tsunami waves inverse problem.