Ad Reniers

• Delft University of Technology

Temporary permeable structures of bamboo and brushwood have been implemented for mangrove restoration along retreating coastlines worldwide. However, deriving lessons from previous studies is inhibited by their lack of morphodynamic context, with missing bathymetric data or control comparisons. In this paper, we present a low-tech, low-cost, data c...

Beach groundwater and nearshore hydrodynamic data were collected during a field experiment along two dissipative beach transects on Galveston Island, Texas, in the fall of 2023. The monitored beaches serve as nesting habitat for the critically endangered Kemp’s ridley sea turtle. Conditions ranged from calm to stormy, with two storms occurring duri...

Aeolian sand strips are bedforms that often form on the beach during high wind events. The sand strips can move across the beach resulting in sediment transport, but these sediment fluxes have not yet been quantified. Permanent laser scanning (PLS) provides an opportunity to gather long-term and detailed information about sand strips. Here, we pres...

In spectral wave models, the nonlinear triad source term accounts for the transfer of energy to the bound higher harmonics. This paper presents an extension to commonly used spectral models that resolves the evolution of the bound wave energy by keeping track of the energy that has been bound by the triad interactions. This extension is referred to...

High-resolution wave measurements at intermediate water depth are required to improve coastal impact modeling. Specifically, such data sets are desired to calibrate and validate models, and broaden the insight on the boundary conditions that force models. Here, we present a wave data set collected in the North Sea at three stations in intermediate...

Infragravity (IG) waves are relatively long waves with typical periods of several tens of seconds to several minutes. The energy at the IG band plays an important role in nearshore areas. For example, IG waves can significantly contribute to dune erosion and sediment transport (e.g., Roelvink et al., 2009), and may excite harbor oscillations (e.g.,...

Nearshore hydro- and morphodynamic data were collected during a field experiment under calm conditions, moderate conditions, and storm conditions with dune erosion in the collision regime. The experiment was conducted on the Sand Engine near Kijkduin, the Netherlands, from October 18, 2021, to January 7, 2022. Two artificial unvegetated dunes were...

High-resolution wave measurements at intermediate water depth are required to improve coastal impact modeling. Specifically, such data sets are desired to calibrate and validate models, and broaden the insight on the boundary conditions that force models. Here, we present a wave data set collected in the North Sea at three stations in intermediate...

A field campaign was carried out at a sheltered sandy beach with the aim of gaining new insights into the driving processes behind sheltered beach morphodynamics. Detailed measurements of the local hydrodynamics, bed-level changes and sediment composition were collected at a man-made beach on the leeside of the barrier island Texel, bordering the M...

The present work presents physical laboratory measurements of surface elevation and pore water pressures in a fine sand bed under bichromatic waves in a large‐scale laboratory experiment. This was done at three cross‐shore locations in the swash zone, with pressures being measured at different depths in the bed. The measurements show that the pore...

A field campaign was carried out at a sheltered sandy beach with the aim of gaining new insights into the driving processes behind sheltered beach morphodynamics. Detailed measurements of the local hydrodynamics, bed level changes and sediment composition were collected at the man-made beach on the leeside of the barrier island Texel, bordering the...

Mangroves protect tropical coastlines from flooding and erosion, reducing flood risks along coastal communities worldwide. Nevertheless, mangrove forests have experienced considerable losses due to activities like urbanization and aquaculture, exposing coastal areas to wave attack. To restore mangroves at eroding coastlines, structures formed by ba...

Traditionally, many numerical studies of sediment transport or morphodynamics in the swash zone use depth-averaged approach. This is relatively computationally cheap, however, the assumptions it makes on vertical structures of the flow velocity and suspended sediment concentration are not always fully met. Depth-resolving models, albeit more comput...

Infragravity (IG) waves are key drivers for coastal erosion and thus need to be properly included in process-based modelling of coastal hazards. Uncertainties remain regarding the offshore boundary conditions for these long waves. Typically, only bound IG waves are included at the boundary, which means that the possible contribution of free IG wave...

Both magnitude and directions of infragravity (IG) waves are essential information for accurate hindcast/prediction of coastal hazard due to stormy waves (e.g., coastal inundation and beach erosion). However, conventional reconstruction methods of directional spectra relying on linear wave theory are not applicable to IG waves which are composed of...

The generation and propagation of infragravity waves at sandy coasts has received significant attention (e.g. Herbers et al., 1994). This is in contrast with tidal inlets where both observations and modeling studies are scarce. Here we present novel observations and modeling of infragravity waves over an ebb-tidal delta located at Ameland, the Neth...

Grain size affects the rates of aeolian sediment transport on beaches. Sediment in coastal environments typically consists of multiple grain‐size fractions and exhibits spatiotemporal variations. Still, conceptual and numerical aeolian transport models are simplified and often only include a single fraction that is constant over the model domain. I...

Weyl rule of association, proposed by Hermann Weyl for quantum mechanics applications (Weyl, 1931), can be used to associate between the dispersion relation of water waves and a non-local pseudo-differential operator. The central result of this study is that this operator correctly approximates the Dirichlet-to-Neumann operator derived for linear w...

Grain size affects the rates of aeolian sediment transport on beaches. Sediment in coastal environments typically consists of multiple grain size fractions and exhibits spatiotemporal variations. Still, conceptual and numerical aeolian transport models are simplified and often only include a single fraction that is constant over the model domain. I...

Currents can affect the evolution of waves in nearshore regions through altering their wavenumber and amplitude. Including the effect of ambient currents (e.g., tidal and wind-driven) on waves in phase-resolving wave models is not straightforward as it requires appropriate boundary conditions in combination with a large domain size and long simulat...

In sandy beach systems, the aeolian sediment transport can be governed by the vertical structure of the sediment layers at the bed surface. Here, data collected with a newly developed sand scraper is presented to determine high‐resolution vertical grain size variability and how it is affected by marine and aeolian processes. Sediment samples at up...

Cheniers are ridges consisting of coarse‐grained sediments, resting on top of the fine sediment that forms the otherwise muddy coast. In this paper, we use Delft3D to explore how cheniers are formed through wave winnowing. We identify three phases of chenier development: (a) a winnowing phase, during which mud is washed out of the seabed initially...

We present a fully coupled 2DV morphodynamic model, implemented in OpenFOAM® that is capable of simulating swash-zone morphodynamics of sandy beaches. The hydrodynamics are described by the Reynolds-averaged Navier–Stokes (RANS) equations with a k−ω turbulence model and the Volume of Fluid (VoF) approach for discriminating between air and water. Se...

Understanding directional spectra of infragravity (IG) waves composed of free and bound components is required due to their impacts on various coastal processes (e.g., coastal inundation and morphological change). However, conventional reconstruction methods of directional spectra relying on linear wave theory are not applicable to IG waves in inte...

To address the important research question of whether implicit (bottom friction) or explicit (stem drag) dissipation models are most appropriate for the prediction of wave attenuation due to aquatic vegetation, the Simulating Waves Nearshore (SWAN) spectral wave model has been extended with an explicit frequency-dependent dissipation model for subm...

A chenier is a beach ridge, consisting of sand and/or shells, overlying a muddy substrate. In this paper, we explore the cross-shore dynamics of cheniers in their ‘active’ phase, i.e. the phase between their formation and their landing on the shore and can no longer be reached by daily wave and tidal influences. While cheniers described in literatu...

The Simulating WAves Nearshore (SWAN) model has been extended with an infragravity module to predict the Wave-Group-Forced (WGF) infragravity response to a frequency-directional sea-swell spectrum at a mildly sloping alongshore uniform beach. To that end the SWAN model has been extended with an WGF-infragravity source term denoted Ssb where the sub...

Plain Language Summary Infragravity waves are long period surface waves that are small in the ocean but much larger in the shallow waters closer to the coast. In coastal regions, they are known to affect coastal safety assessments as they can, for example, impact the overtopping of coastal structures, enhance the erosion of dunes, and trigger the r...

In numerical ocean models, the effect of waves on currents is usually expressed by either vortex-force or radiation stress representations. In this paper, the differences and similarities between those two representations are investigated in detail in conditions of both conservative and nonconservative waves. In addition, comparisons between differ...

Mangrove vegetation constitutes a natural coastal defence against waves and erosion. Despite their protective role, mangrove ecosystems have experienced continuous degradation over the last decades due to human causes. At retreating mangrove coastlines, bamboo structures are built to create new habitat for mangrove colonization. Existing structures...

Seaport operability is key to the economic viability of ports. Metocean conditions (e.g., wind, short waves, and infragravity waves) affect this operability when certain thresholds are exceeded. This paper describes a method for the global mapping of seaport operability risk indicators using open-source metocean data. This global-scale assessment p...

In this paper, a new approach to model wave-driven, cross-shore shoreline change incorporating multiple timescales is introduced. As a base, we use the equilibrium shoreline prediction model ShoreFor that accounts for a single timescale only. High-resolution shoreline data collected at three distinctly different study sites is used to train the new...

A Correction to this paper has been published: https://doi.org/10.1038/s41597-021-00874-2.

A 2-layer non-hydrostatic model with improved dispersive behaviour is presented. Due to the assumption of a constant non-hydrostatic pressure distribution in the lower layer, the dispersive behaviour is improved without much additional computational time. A comparison with linear wave theory showed that this 2-layer model gives a better result for...

Coastal safety assessments with wave-resolving storm impact models require a proper offshore description for the incoming infragravity (IG) waves. This boundary condition is generally obtained by assuming a local equilibrium between the directionally-spread incident sea-swell wave forcing and the bound IG waves. The contribution of the free inciden...

High quality laboratory measurements of nearshore waves and morphology change at, or near prototype-scale are essential to support new understanding of coastal processes and enable the development and validation of predictive models. The DynaRev experiment was completed at the GWK large wave flume over 8 weeks during 2017 to investigate the respons...

The prediction of wave runup, as well as its components, time-averaged setup and the time-varying swash, is a key element of coastal storm hazard assessments, as wave runup controls the transitions between morphodynamic response types such as dune erosion and overwash, and the potential for flooding by wave overtopping. While theoretically able to...

Most numerical studies of sediment transport in the swash zone use depth-averaged models. However, such models still have difficulty predicting transport rates and morphodynamics. Depth-resolving models could give detailed insight in swash processes but have mostly been limited to hydrodynamic predictions. We present a depth-resolving numerical mod...

Waves are important drivers for reef hydrodynamics, and therefore strongly contribute to flooding over reef-lined coasts. While high-frequency waves are largely dissipated when they propagate over the reef flat due to breaking and friction, low-frequency (LF) waves are generally able to reach the back-reef beach. There, they can reflect and form (q...

Cheniers are important for stabilising mud-dominated coastlines. A chenier is a body of wave-reworked, coarse-grained sediment consisting of sand and shells overlying a muddy substrate. In this paper we present and analyse a week of field observations of the dynamics of a single chenier along the coast of Demak, Indonesia. Despite relatively calm h...

A large-scale field campaign was carried out on the ebb-tidal delta (ETD) of Ameland Inlet, a basin of the Wadden Sea in the Netherlands, as well as on three transects along the Dutch lower shoreface. The data have been obtained over the years 2017–2018. The most intensive campaign at the ETD of Ameland Inlet was in September 2017. With this campai...

Sediment transport over intertidal flats is driven by a combination of waves, tides, and wind-driven flow. In this study we aimed at identifying and quantifying the interactions between these processes. A five week long dataset consisting of flow velocities, waves, water depths, suspended sediment concentrations, and bed level changes was collected...

Intertidal bars are naturally occurring morphological features along the waterline of sandy beaches. Present quantitative knowledge on intertidal bar behavior is limited, due to the scarcity of data resources and the limitations of traditional survey techniques. To investigate and quantify the cross-shore morphologic behavior of intertidal bars, ho...

Considering the likely increase in coastal flooding in small island developing states (SIDSs) due to climate change, coastal managers at the local and global levels have been developing initiatives aimed at implementing disaster risk reduction (DRR) and adaptation measures. Developing science-based adaptation policies requires accurate coastal floo...

The nonlinear wave shape, expressed by skewness and asymmetry, can be calculated from surface elevation or pressure time series using bispectral analysis. Here, it is shown that the same analysis technique can be used to calculate the bound superharmonic wave height. Using measured near-bed pressures from three different field experiments, it is de...

Modelling statistical wave interferences over shear currents - Volume 891 - Gal Akrish, Pieter Smit, Marcel Zijlema, Ad Reniers

Many coral reef-lined coasts are low-lying with elevations <4 m above mean sea level. Climate-change-driven sea-level rise, coral reef degradation, and changes in storm wave climate will lead to greater occurrence and impacts of wave-driven flooding. This poses a significant threat to their coastal communities. While greatly at risk, the complex hy...

Abstract. A large-scale field campaign has been carried out on the ebb-tidal delta (ETD) of Ameland Inlet, a basin of the Wadden Sea in the Netherlands, as well as on three transects along the Dutch lower shoreface. With this campaign, as part of KustGenese2.0 (Coastal Genesis 2.0) and SEAWAD, we aimed to gain new knowledge on the processes driving...

Although commonly used for the validation of morphological predictions, point-wise accuracy metrics, such as the root-mean-squared error (RMSE), are not well suited to demonstrate the quality of a high-variability prediction; in the presence of (often inevitable) location errors, the comparison of depth values per grid point tends to favour predict...

Abstract. Considering the likely increase of coastal flooding in Small Island Developing States (SIDS), coastal managers at the local and global level have been developing initiatives aimed at implementing Disaster Risk Reduction (DRR) measures and adapting to climate change. Developing science-based adaptation policies requires accurate coastal fl...

Field measurements of waves and currents were obtained at ten locations on an ebb-tidal shoal seaward of Ameland Inlet for a six-week period. These measurements were used to investigate the evolution of the near-bed velocity skewness and asymmetry, as these are important drivers for wave-induced sediment tranport. Wave shape parameters were compare...

A large-scale laboratory experiment was completed to investigate the performance of a dynamic cobble berm revetment designed to provide sustainable coastal protection under wave attack and a rising water level. The experiment demonstrated the inherent stability of the dynamic revetment, which was observed to be reshaped by every wave but retained i...

In process-based numerical models, reducing the amount of input parameters, known as input reduction (IR), is often required to reduce the computational effort of these models and to enable long-term, ensemble predictions. Currently, a comprehensive performance assessment of IR-methods is lacking, which hampers guidance on selecting suitable method...

Surfzone mixing and transport on a sandy, steep (∼1/8 slope), reflective beach at Carmel River State Beach, California, are described for a range of wave and alongshore flow conditions. Depth-limited wave breaking occurred close to the shore due to the steepness of the beach, creating a narrow surf/swash zone (∼10 m wide). Fluorescent Rhodamine dye...

In order to improve the current aeolian modeling, a process-based model is developed by implementing biological and physical processes adapted from different existing models. The current version of the model is capable of simulating barchan and parabolic dunes and the initial stage of coastal dune formation: Embryo dunes. Potentially the model can...

A two-dimensional, barotropic numerical model was employed to investigate the dynamics of tidal wave propagation in the South China Sea with a particular interest for its characteristics along the Mekong deltaic coast. The study indicates that tidal waves propagate from the Pacific Ocean into the South China Sea mainly through the Luzon Strait (LS)...

In the light of challenges raised by a changing climate and increasing population pressure in coastal regions, it has become clear that theoretical models and scattered experiments do not provide the data we urgently need to understand coastal conditions and processes. We propose a Dutch coastline observatory named ICON.NL, based at the Delfland Co...

Several studies have reported the development of undular bores over fringing coral reefs (e.g, Gallagher, 1976; Nwogu and Demirbilek, 2010) but the importance of this phenomenon for reef hydrodynamics has never been studied. Yet, the transformation of a long wave (e.g., swell or infragravity wave) into an undular bore leads to significant modificat...

This study presents an efficient approach of resolving wave interference patterns in spectral wave models (e.g., SWAN). Such interference patterns, which frequently occur in coastal waters (e.g., near headlands, harbor entrances and coastal inlets), may lead to rapid changes in wave statistics, and thus, can affect wave-driven flow and transport pr...

Sediment transport by currents and waves determines the evolution of shoals and channels on the ebb-tidal delta. The channels are an important conduit for shipping and are often dredged to maintain access at considerable cost. A better understanding of the sediment transport processes within the channels is the basis for a more cost-effective maint...

Nearshore sandbar patterns can affect the hydrodynamics and, as a result, the beach morphodynamics in the nearshore zone. Hence, spatial and temporal variability in the sandbars can influence beach accretion and erosion. Understanding the variability of the sandbar system can therefore be crucial for informed coastal zone management. So far, the me...

Understanding long-term sandbar dynamics can be crucial for informed coastal zone management, but is often hampered by data availability. To increase the number of sandbar observations available from bathymetric surveys, this study proposes and evaluates a method to manually extract the sandbar location using freely available satellite imagery for...

Wave-supported gravity flows (WSGFs) generate rates of sediment flux far exceeding other cross-shelf transport processes, contributing disproportionately to shelf morphology and net cross-shelf fluxes of sediment in many regions worldwide. However, the conditions deemed necessary for the formation of WSGF limit them to a narrow set of shelf conditi...

We investigated whether cross-shore distributions of coastal phytoplankton to the surf zone are controlled by hydrodynamics and their biological characteristics. Data from a rip-channeled beach indicate that concentrations of phytoplankton are higher in the surf zone than offshore. To examine how phytoplankton is transported toward the shore, we us...

The Sea Surface KInematics Multiscale monitoring (SKIM) mission proposes to use Doppler-based measurements of velocities to provide global estimates of surface currents and ice drift at spatial scales of 40 km and more, with snapshots at least every day for latitudes 75 to 82, and every few days otherwise. Given the contribution of wave motion to D...

We propose a satellite mission that uses a near-nadir Ka-band Doppler radar to measure surface currents, ice drift and ocean waves at spatial scales of 40 km and more, with snapshots at least every day for latitudes 75 to 82∘, and every few days for other latitudes. The use of incidence angles of 6 and 12∘ allows for measurement of the directional...

Operational nearshore current forecasts based on numerical model simulations are gaining popularity as a measure to increase the safety of swimmers. Applying remotely-sensed bathymetry in these model simulations is often proposed in order to cope with rapidly changing nearshore bathymetry. Errors in the remotely-sensed bathymetry may negatively aff...

The Deepwater Horizon oil spill damaged some beaches along the Northern Gulf of Mexico (NGoMex) coast more than others, possibly related to the presence of natural protection mechanisms. In order to optimize future mitigation efforts to protect the coast, these mechanisms should be understood. The NGoMex coast is characterized by relatively long st...

The behaviour of subtidal sandbars can be strongly influenced by the introduction of sand nourishments in the coastal system. This study focuses on the impact of nourishments on subtidal bar behaviour at spatio-temporal scales beyond a single nourishment project. It aims to determine the long-term behaviour of subtidal sandbars along an entire coas...