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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 Marsdiep basin that is part of the Dutch Wadden Sea. The dataset consists of (1) current, wave and turbidity measurements from a dense cross-shore array and a 3ĝ€¯km alongshore array; (2) sediment composition data from beach surface samples; (3) high-Temporal-resolution RTK-GNSS beach profile measurements; (4) a pre-campaign spatially covering topobathy map; and (5) meteorological data. This paper outlines how these measurements were set up and how the data have been processed, stored and can be accessed. The novelty of this dataset lies in the detailed approach to resolve forcing conditions on a sheltered beach, where morphological evolution is governed by a subtle interplay between tidal and wind-driven currents, waves and bed composition, primarily due to the low-energy (near-Threshold) forcing. The data are publicly available at 4TU Centre for Research Data at: 10.4121/19c5676c-9cea-49d0-b7a3-7c627e436541 .

Introduction Accurately predicting cross-shore sediment transport remains a challenging task as it comprises many physical processes, which are often comparable in magnitude, but vary in terms of sign. Numerical wave tanks using Reynolds-Averaged Navier-Stokes (RANS) turbulence models can potentially resolve many of these processes, and may be used as powerful tools to study the detailed sediment transport processes, which are often difficult to measure in the laboratory and field. In past studies using RANS models to simulate waves, there has been a tendency to overestimate turbulence, however. This problem was solved by Larsen and Fuhrman (2018), where significant improvements in predicted turbulence levels and undertow profiles for a simulated model scale experiment were demonstrated. In this work, the new model will be used to simulate a large-scale experiment with a special focus on hydrodynamic processes relevant for cross-shore sediment transport, such as wave boundary layer flow, undertow and turbulence. Methods and Results A recent experimental campaign conducted in a 100 m long wave flume involving bichromatic waves breaking over a fixed bar (van der Zanden et al., 2019) will be simulated using the OpenFOAM solver waves2FOAM (Jacobsen et al. 2012), combined with the model by Larsen and Fuhrman (2018). Figure 1 shows a comparison between the experimental and modelled undertow. The model importantly captures the transition in the vertical undertow structure going through the outer surf zone (54 m< x < 60 m), where the undertow goes from having largest negative velocities far from the bed to having largest negative velocities near the bed. This could not be achieved using a standard RANS model. The model results will be compared in detail with experimental results for water surface elevations, velocities and turbulence, and implications for cross-shore sediment transport will be discussed (to be presented).

Feedbacks between geomorphology and plants are increasingly recognized as key drivers shaping a variety of landscapes. Most studies of biogeomorphic interactions have focused on the influence of physical plant characteristics, such as stem and root density, on landscape morphodynamics without considering the role of life-history traits. However, pioneer plants can have very different colonization behaviours. Fast colonizers are characterized by a high number of establishing seedlings that produce homogenous vegetation patterns. In contrast, slow colonizers are characterized by a low number of establishing seedlings that are able to expand laterally, resulting in patchy vegetation patterns. Here we combine biogeomorphic model simulations and field observations in the Western Scheldt Estuary, the Netherlands, to show that colonization behaviour can influence the evolution of wetland landscapes. We find that colonization by fast colonizers favours stabilization of pre-existing channels and consolidation of the landscape configuration. In contrast, colonization by slow colonizers facilitates the formation of new channels and thereby actively facilitates further landscape self-organization. Our findings underline the key role of life-history traits in steering landscape self-organization across different biogeomorphic systems, and potentially the long-term resilience of these landscapes to disturbances.

harvest, Coastal Engineering

cBathy is a recently developed tool designed to predict the nearshore bathymetry using Argus images. The algorithm estimates the water depth in a predefined analysis domain. For each analysis location the dominant wave frequencies are detected through spectral analysis while the wavenumber is given by the phase structure of the first EOF of the cross spectral matrix. Subsequently the linear dispersion relationship is inverted and solved yielding a depth estimate. However, past studies have found the latter to be inaccurate in a nonlinear environment. The current work aims at both the application of cBathy in the Dutch coast of Egmond aan Zee and the improvement of the algorithm in the surf zone by testing different nonlinear celerity predictors. The algorithm is well compared with field measurements over a big domain and for the offshore part. A closer examination in the intertidal zone and over a cross shore transect reveals that cBathy predicts celerity systematically higher than linear theory. Errors of O(0.5 m) are found inside the inner surf zone where a composite model for phase speed that incorporates both amplitude and dispersion effects predicts better the bathymetry. Higher errors occur on the difficult to be modeled location of the onset of breaking (O(1 m)) where the solitary model matches better with the ground truth data. In addition, performance of the algorithm substantially degrades during stormy conditions due to camera issues with bathymetric errors being O(>1 m).

This paper presents a comprehensive numerical study into the infragravity-wave dynamics at a field site, characterized by a gently sloping barred beach. The nonhydrostatic wave-flow model SWASH was used to simulate the local wavefield for a range of wave conditions (including mild and storm conditions). The extensive spatial coverage of the model allowed us to analyze the infragravity-wave dynamics at spatial scales not often covered before. Overall, the model predicted a wavefield that was representative of the natural conditions, supporting the model application to analyze the wave dynamics. The infragravity-wave field was typically dominated by leaky waves, except near the outer bar where bar-trapped edge waves were observed. Relative contributions of bar-trapped waves peaked during mild conditions, when they explained up to 50% of the infragravity variance. Near the outer bar, the infragravity-wave growth was partly explained by nonlinear energy transfers from short waves. This growth was strongest for mild conditions, and decreased for more energetic conditions when short waves were breaking at the outer bar. Further shoreward, infragravity waves lost most of their energy, due to a combination of nonlinear transfers, bottom friction, and infragravity-wave breaking. Nonlinear transfers were only effective near the inner bar, whereas near the shoreline (where losses were strongest) the dissipation was caused by the combined effect of bottom friction and breaking. This study demonstrated the model's potential to study wave dynamics at field scales not easily covered by in situ observations., Hydraulic Engineering, Civil Engineering and Geosciences

Surface moisture is an important supply limiting factor for aeolian sand transport, which is the primary driver of coastal dune development. As such, it is critical to account for the control of surface moisture on available sand for dune building. Optical remote sensing has the potential to measure surface moisture at a high spatio-temporal resolution. It is based on the principle that wet sand appears darker than dry sand: it is less reflective. The goals of this study are (1) to measure and model reflectance under controlled laboratory conditions as function of wavelength () and surface moisture () over the optical domain of 350–2500 nm, and (2) to explore the implications of our laboratory findings for accurately mapping the distribution of surface moisture under natural conditions. A laboratory spectroscopy experiment was conducted to measure spectral reflectance (1 nm interval) under different surface moisture conditions using beach sand. A non-linear increase of reflectance upon drying was observed over the full range of wavelengths. Two models were developed and tested. The first model is grounded in optics and describes the proportional contribution of scattering and absorption of light by pore water in an unsaturated sand matrix. The second model is grounded in soil physics and links the hydraulic behaviour of pore water in an unsaturated sand matrix to its optical properties. The optical model performed well for volumetric moisture content 24% ( 0.97), but underestimated reflectance for between 24–30% ( 0.92), most notable around the 1940 nm water absorption peak. The soil-physical model performed very well ( 0.99) but is limited to 4% 24%. Results from a field experiment show that a short-wave infrared terrestrial laser scanner ( = 1550 nm) can accurately relate surface moisture to reflectance (standard error 2.6%), demonstrating its potential to derive spatially extensive surface moisture maps of a natural coastal beach.

Characteristics of the individual wave height distribution in shallow water have been investigated using measured wave data and results of numerical simulations using the non-hydrostatic SWASH model. It is shown that the SWASH model is capable of reproducing the temporal and spatial variation of surface elevation in a wave flume and the resulting individual wave height distributions, whereas three theoretical distributions fail to do so. SWASH was also applied to a 2D field case and was able to reproduce the individual wave height distribution. Finally, the effect of directional spreading on the individual wave height distribution was determined by performing two SWASH model runs; one with directional spreading and one with uni-directional irregular waves. The results suggest that directional spreading increases the highest individual wave height., Hydraulic Engineering, Civil Engineering and Geosciences

Input reduction is imperative to long-term (> years) morphodynamic simulations to avoid excessive computation times. Here, we discuss the input-reduction framework for wave-dominated coastal settings introduced by Walstra et al. (2013). The framework comprised 4 steps, viz. (1) the selection of the duration of the original (full) time series of wave forcing, (2) the selection of the representative wave conditions, (3) the sequencing of these conditions, and (4) the time span after which the sequence is repeated. In step (2), the chronology of the original series is retained, while that is no longer the case in steps (3) and (4). The framework was applied to two different sites (Noordwijk, Netherlands and Hasaki, Japan) with multiple nearshore sandbars but contrasting long-term offshore-directed behavior: at Noordwijk the offshore migration is gradual and not coupled to individual storms, while at Hasaki the offshore migration is more episodic, and wave chronology appears to control long-term evolution. The performance of the model with reduced wave climates was referenced to a simulation with the actual (full) wave-forcing series. It was demonstrated that input reduction can dramatically affect long-term predictions, even to such an extent that the main characteristics of the offshore bar cycle are no longer reproduced. This was particularly the case at Hasaki, where all synthetic series that no longer capture the initial chronology (steps 3 and 4) lead to rather unrealistic long-term simulations. At Noordwijk, synthetic series can result in realistic behavior, provided that the time span after which the sequence is repeated is not too large; the reduction of this time span has the same positive effect on the simulation as increasing the number of selected conditions in step 2. It was further demonstrated that, although storms result in the largest morphological change, conditions with low to intermediate wave energy must be retained to obtain realistic long-term sa, Hydraulic Engineering, Civil Engineering and Geosciences

This paper aims to conceptually simulate observed spatial and temporal variability in aeolian sediment transport rates, erosion and deposition on a beach. Traditional strategies of modeling aeolian sediment transport rates do not account for supply limitations that are common on natural beaches. A recently developed 1D linear advection model is used in which supply limitations are taken into account in a highly aggregated manner. It is shown that the model is able to simulate the appearance and disappearance of sediment accumulations. However, sediment accumulations alike observed in the field using ARGUS cameras behave on a different time and spatial scales., Hydraulic Engineering, Civil Engineering and Geosciences

Cross-shore suspended sediment transports were studied at a transect over a beach plain in a small tidal inlet system The Slufter located on the barrier island Texel, The Netherlands. Field measurements of the near-bed velocity and sediment concentrations were obtained using electromagnetic current meters and optical backscatter sensors. Spectral analyses of velocity and sediment concentration was performed on two time frames of low wave conditions and two time frames of high wave conditions to reveal the contributions of waves of different frequencies to the net transport. Sediment flux measurements showed that the main contributors to the gross suspended sediment transport were made by incident waves and undertow, causing onshore and offshore transport, respectively. Co-spectral density diagrams of high wave conditions have shown a high-frequency contribution to the onshore transport, but of minor importance to the gross suspended sediment transport. Morphological change over the cross-section was mapped with a DGPS system and by using depth-of-activity rods. Swash bars were formed and slowly migrated onshore during low wave conditions and the cross-shore profile flattened during high wave events.

A large multi-institutional nearshore field experiment was conducted at Truc Vert, on the Atlantic coast of France in early 2008. Truc Vert’08 was designed to measure beach change on a long, sandy stretch of coast without engineering works with emphasis on large winter waves (offshore significant wave height up to 8 m), a three-dimensional morphology, and macro-tidal conditions. Nearshore wave transformation, circulation and bathymetric changes involve coupled processes at many spatial and temporal scales thus implying the need to improve our knowledge for the full spectrum of scales to achieve a comprehensive view of the natural system. This experiment is unique when compared with existing experiments because of the simultaneous investigation of processes at different scales, both spatially (from ripples to sand banks) and temporally (from single swash events to several spring-neap tidal cycles, including a major storm event). The purpose of this paper is to provide background information on the experiment by providing detailed presentation of the instrument layout and snapshots of preliminary results., Hydraulic Engineering, Civil Engineering and Geosciences

To study onshore bar migration and the accompanying intra-wave sediment transport a wave flume experiment was conducted. The wave flume had a rigid bottom with a single bar profile. The focus of the experiment was to measure the hydrodynamics in the wave bottom boundary layer. The results show that the skewness of bottom stress is not only related to wave skewness but also to wave asymmetry., Hydraulic Engineering, Civil Engineering and Geosciences

Morphological evolution of coasts is mainly determined by hydrodynamics and sediment transport processes. One of the present-day bottlenecks in predicting morphological change, concerns the description of the vertical distribution of cross-shore sediment transport and the description of associated vertical sediment concentration profiles. The prediction of these sediment concentration profiles requires specification of the sediment diffusivity, which is proportional to the vertical derivative of the sediment concentration. In existing models the distribution of the sediment diffusivity over depth varies between a constant, linear, parabolic or even a constant-linear-constant distribution. This thesis aims to determine diffusivity profiles based on time-averaged concentration profiles under skewed waves, from ripple to sheet flow regime. Full-scale experiments were done in the large scale wave flume, GWK, Gro{\ss}er Wellen Kanal, Hannover, Germany. The experiments have produced a data set of bed states, hydrodynamic conditions and time- and height-varying concentration measurements for the ripple and sheet flow regime for two different sediments Analysis of time-averaged data from a triple-frequency Acoustic Backscatter Sensor (ABS), attached to the `Twente-Utrecht measurement frame', provided time-averaged vertical sediment concentration profiles, from which the sediment diffusivity profiles were computed. For all conditions, the measured diffusivity profile has a parabolic shape. Uncertainty of the magnitude of the background signal of the ABS causes large uncertainty in the dimensions of sediment concentrations. However, the dimensions of sediment diffusivities are comparable to sediment diffusivities determined from existing empirical formulations. A comparifson to existing formulations resulted in a best fit of shape and dimensions to the diffusivity predictor of Bijker (1971).

De huidige studie is uitgevoerd in het kader van de doelfinanciering V&W met als onderwerp `Veerkracht van de kust' . In de berekeningswijze van de veerkracht (Baan et al ., 1999) wordt gebruik gemaakt van een parameter die de dynamiek in de duinvoetpositie voor een kustraai beschrijft. Hierbij wordt onder dynamiek de fluctuaties ('veerkracht') van de duinvoet rond een trend verstaan . Baptist & Van den Boogaard (2000) stellen voor om 1 .96*standaard deviatie (a) van de residuen te gebruiken als parameter voor de dynamiek van de duinvoet. Voorts constateren zij dat de duinvoetdynamiek langs de Noord-Hollandse gekenmerkt wordt door bepaalde perioden, in de orde van 12 tot 15 jaar, orde 30 tot 40 jaar, en rond de 55 jaar . Het is echter onduidelijk in hoeverre deze dominante periodes ook daadwerkelijk statistische significant zijn en wat hun relatieve belang is. Verder beschouwden Baptist & Van den Boogaard (2000) alle raaien afzonderlijk, daarbij de eventueel aanwezige ruimtelijke samenhang in duinvoet dynamiek verwaarlozend. De voorliggende studie richtte zich op het bepalen van bovengenoemde ruimtelijke en temporele aspecten van de duinvoet dynamiek. Hierbij werd verondersteld dat het morfologisch gedrag van de duinvoet bestaat uit een trend en een residu, waarbij het residu kan worden onderverdeeld in een kustlangs uniform en een kustlangs niet-uniform deel . Het uniforme deel (2D-gedrag) hangt samen met stormen, het kustlangs niet-uniforme deel (3D-gedrag) hangt samen met strandzandgolven . Om deze hypothese te toetsen is voor drie kustgebieden de morfologische dynamiek van de duinvoet geanalyseerd . Het betreft de kustvakken Noord- Holland en Rijnland langs de gesloten Hollandse kust en het kustvak Walcheren langs de open Zeeuwse kust. Uit de diverse analyses blijkt dat de morfologische dynamiek van de duinvoet op een tijdschaal van jaren tot decennia wordt bepaald door de residuen . Naarmate de beschouwde tijdschaal toeneemt wordt de trend belangrijker . Het ku