Dune Erosion Research Articles

Formation Processes and Environments in the Hinojo‐Las Tunas Shallow Lake System, Argentina Pampas: The Laguna Chica Archaeological Locality as a Case Study

ABSTRACTThis work integrates taphonomic (archaeofaunistics and bioarchaeology) and geoarchaeological (geormorphology, pedologic, sedimentological and micromorphological analyses) information to discuss the depositional and postdepositional history of both surface and buried archaeological record related to past hunter–gatherer populations from the Central Pampean Dunefields of Argentina (South America). Radiocarbon and optically stimulated luminescence dating suggest three temporal clusters of occupations in the Laguna Chica locality: one during the middle Holocene (~8050–6535 years cal. B.P.) and two in the late Holocene (~3350–2870 and ~1640–1535 years cal. B.P.). Middle Holocene burials found at the present lake shore are hosted in aeolian sediments that accumulated under arid/semiarid conditions. Modern lacustrine dynamics derived from contraction/expansion cycles have exposed burials, archaeofauna, and stone tools, resulting in displacements, fragmentation and loss. A palimpsest of cultural and natural material spanning ~8000 years resulted from this paleoenvironmental setting. Late Holocene human activities might have been related to a transitional landscape, where aeolian processes took place under an expanding lacustrine scenario (i.e., relatively wetter conditions). Our stratigraphic assessment suggests that human occupations were syndepositional agents with episodes of aeolian sand activity and landscape stability. The taphonomic and geoarchaeological evidence from Laguna Chica locality show that the empirical evidence traditionally used to evaluate hunter–gatherer settlement patterns (e.g., abundance and diversity of archaeological evidence and their spatial association in surface or stratigraphic units) and human diet breadth changes (e.g., Ntaxa) may simply reflect the cumulative action of lacustrine erosion of dunes. While both the Laguna Chica surface and stratigraphic records have complex formation histories, the buried context could be interpreted with greater detail through taphonomic and sedimentological analyses.

Fluvial-lacustrine influences on linear dune erosion at Lake Caroline in the Simpson Desert of Australia

Linear dunes are frequently examined with regard to their formation and maintenance; however, erosion or degradation of these landforms is less commonly addressed, due in part to the lack of observable changes in the geologic record. This study investigates the significant erosion of linear dunes along Lake Caroline, a playa in the northern Simpson Desert of central Australia. Field observations, laboratory analyses, and remote sensing imagery document recent fluvial and lacustrine interactions at Lake Caroline. Compositional and geochemical sediment analyses from three ∼2 m deep hand-augured sample sites indicate that the playa is primarily filled with sand from linear dunes, but also contains evaporite minerals and weathered local bedrock. Satellite images show that the playa has flooded at least 58 times since 2001. Our results indicate that present-day aeolian processes are sufficient to mobilize and transport sediment but are dominated by fluvial-lacustrine processes, resulting in the playa-adjacent dunes becoming isolated and starved of local sediment. As a result, the dunes are currently eroding into the playa which supports the conclusion that long-distance sediment transport is not responsible for the formation or maintenance of linear dunes as suggested by the linear due extension hypothesis. Burial dates from optically stimulated luminescence (OSL) indicate the linear dunes have been eroding for as much as 24 ka, and sediment samples from the playa near one linear dune suggest an onset of dune formation in the area before 58 ka. This work documents an instance in geologic time during the late Quaternary when aeolian, fluvial, and lacustrine processes are competing with one another, offering new insights into the dynamics of linear dunes in the arid Simpson Desert.

Coastal Dune Erosion and Slumping Processes in the Swash‐Dune Collision Regime Based on Field Measurements

AbstractThis paper studies hydrodynamic and morphodynamic field measurements of two storms with dune erosion in the swash‐dune collision regime. It analyses (a) the behavior and change of the total dune profile over the course of both storms (b) the erosion rate at the dune base, (c) the slumping frequency, and (d) the volumes of individual slumps. The erosion rate at the dune base shows a strong positive correlation with the square of the total water levels that were exceeded for 2% of the time, recorded approximately 5–6 m in front of the dune face (r = 0.91). Individual slumping events occurred when nearly all sediments from previous slumps at the dune base were transported away from the dune. A strong positive correlation was found between the time between two consecutive slumps, and the volume of the first slump divided by the mean erosion rate between the two slumps (r = 0.90). As a consequence, smaller slumps were followed more rapidly by a new slump than larger slumps, under identical erosion rates. The majority of the slumping events occurred after the last wave impact before a slumping event, when the instantaneous water level in front of the dune was still retreating. No clear process based on the incident hydrodynamics could be identified that determined the size of individual slumps. Overall, the results of this study suggest that the morphodynamic behavior of the upper dune face and dune crest is primarily steered by the erosion at the dune base.

Coastal dune management affects above and belowground biotic characteristics.

Dune vegetation mediates dune-building through trapping wind-blown sand and reduces dune erosion by attenuating wave energy via above- and belowground biomass. Despite the role of vegetation in dune functions, the amount and distribution of biomass within a dune remains poorly quantified due to a lack of ample data. Our objectives were to determine the effects of management history and elevation on (1) dune belowground biotic structure and aboveground community composition and (2) to determine best predictors of belowground biomass. We sampled belowground biomass and sedimentology across the dune profile at sites in the Outer Banks, North Carolina, USA. Dunes were classified as either unmanaged (no anthropogenic interventions) or managed (sand fencing, vegetation planting, dune construction). Living belowground biomass was higher in unmanaged dunes and decreased with depth. Non-living belowground biomass was 50% higher than living biomass and with greater abundance in unmanaged dunes. Elevation was a significant covariate of living and non-living belowground biomass, vegetative cover and species richness. Plant community composition varied less in managed dunes and differed significantly from unmanaged dunes. Vegetative cover, species richness, elevation, sedimentology and management history were predictors of belowground biomass. These results underscore the influence of management and geomorphology on dune plant communities, which may influence erosion resistance.

Seasonality of aeolian landforms on Meridiani Planum, Mars

The wind interacts with the surface of Mars, forming aeolian landforms. The orientation of these landforms informs us about the formative wind directions. The observations of the orientation of aeolian landforms on Meridiani Planum between Mars years 26 and 38 indicated that there is a seasonality of formative wind directions in this region. The studied landforms were shaped by a predominant SE wind during summer, while during winter several wind directions played a role in their formation. Throughout the Mars year, the most formative were the NW winds. The presence of dark wind streaks oriented toward the west during winter indicates that E winds occur in this season on Meridiani Planum, as previously predicted by numerical simulations. It was also found that aeolian deflation led to complete erosion of smaller dunes, and that the relatively strong deflation was responsible for the scarcity of fine-grained ripples on Meridiani Planum. In this region, fine-grained ripples were found only in a few locations, and they were mainly small bedforms with wavelengths up to several centimeters.

Evaluating Vegetation Effects on Wave Attenuation and Dune Erosion during Hurricane

This study employs the XBeach surfbeat model (XBSB) to explore the effects of vegetation on wave attenuation and dune erosion in a case study of Mexico Beach during Hurricane Michael. The XBSB model was validated against laboratory experiments of wave-induced dune erosion and wave attenuation by vegetation. In the case study of vegetation on dunes in Mexico Beach during Hurricane Michael, different vegetation drag coefficients were evaluated to investigate the effects of vegetation on wave attenuation and dune erosion. LiDAR data of dune profiles before and after Hurricane Michael were used for model validation. The findings reveal that vegetation on dunes significantly affects wave attenuation and dune erosion. Under vegetated conditions, as the vegetation drag coefficient value increases, wave attenuation also increases, leading to a reduction of dune erosion. An increase in vegetation density enhances wave attenuation in the vegetated area, including reductions in significant wave height and flow velocity. However, the rate of change in attenuation decreases as the vegetation density increases. Through simulations under regular wave condition on Mexico Beach, an optimal vegetation density was identified as 800 units/m2. Beyond this density, additional vegetation does not substantially improve wave attenuation. Furthermore, the position of the dune crest elevation is related to the location where the alongshore flow velocity begins to decrease. The findings highlight the essential role of coastal vegetation in enhancing coastal resilience against hurricanes.

Skill assessment of a total water level and coastal change forecast during the landfall of a hurricane

The Total Water Level and Coastal Change Forecast (TWL&CC Forecast) provides coastal communities with 6-day notice of potential elevated water levels and coastal change (i.e., dune erosion, overwash, or inundation) on sandy beaches that threatens safety, infrastructure, or resources. This continuously operating model provides hourly information for select regions along U.S. Gulf of Mexico and Atlantic Ocean coastlines. The objective of this work is to assess the skill of forecasts during a period of elevated water levels along the coasts of North Carolina (NC) and South Carolina, USA caused by Hurricane Isaias in August 2020, using a combination of observations and model hindcasts. Water levels and waves were observed throughout the storm at three locations near Wrightsville Beach, NC, which provided information to assess forecast skill; a wave buoy offshore, a tide gage at a local pier, and a pressure sensor deployed at the pier. In addition to observations, the non-hydrostatic phase-resolving model SWASH (Simulating WAves till SHore) was forced with hourly wave energy spectra derived from a coupled Delft3D-SWAN simulation during the peak of Isaias, to complement observations by computing nearshore wave height and wave-induced setup and runup at the shoreline. During the storm peak, SWASH-simulated water levels at the sensor position were comparable to those at the maximum landward extent (bias = −0.05 m; gain = 0.26; r2 = 0.99), suggesting that observations at the USGS sensor location were a useful proxy for total water level (TWL; sum of tide, surge and wave runup) at the shoreline that are predicted by the TWL&CC Forecast. The TWL forecast at Wrightsville Beach was consistent with observations from the USGS sensor (bias = −0.38 m and −0.74 m, scatter index = 0.22 and 0.28 for the two forecast model grids considered, respectively; weighted regression considering model uncertainty explained 95 percent of variability in observed TWL). Observed TWL was within the confidence interval of the TWL&CC Forecast for the 5 h at the storm peak. Forecast mean water levels (MWL; sum of tide, surge and wave setup) and tide gage observations were also consistent (bias = 0.07 m and 0.02 m for the forecast model grids; scatter index = 0.46; r2 = 0.80). Forecast MWL at the storm peak was within 0.06 m of the observed MWL from the tide gage for both sites. In the region where Isaias made landfall, eight additional pressure sensors were compared to the peak TWL forecast (bias = 0.14 m; scatter index = 0.18). Forecast TWL explained 90 percent of observed variability in TWL when considering uncertainty of the forecast with a weighted regression. The results demonstrate that wave-driven water levels contributed a significant portion of the forecast TWL during Isaias (52 percent during the three peak hours of the storm), and that TWL were represented using the forecast model. Mean absolute error of the coastal change forecast and observed overwash is 0.4 and 0.14 for the two forecast model grids considered. The skill demonstrated by this computationally efficient method indicates that the forecasting system can provide fast and reliable predictions of TWL across hundreds of km of coastline at sub-km resolution, days to hours in advance of when storms threaten coastal regions.

Statistics of significant storm events using one- and two-dimensional analyses of the natural and protected coasts of the Dziwnów Spit

In this paper, one- and two-dimensional statistical analyses of significant storm parameters were conducted along natural and protected coasts of the Dziwnów Spit, based on quantiles and concentration ellipses. In the one-dimensional analysis, the quantiles of 0.9, 0.99 and 0.999 erosion magnitude D, sea level F, significant wave height H and storm duration T were determined, and these quantiles correspond to significant storm occurrence once every 10, 100 and 1000 years, respectively. To account for the influence of other variables on the erosion magnitude, log-linear models describing the linear dependence of log(D) on F and log(D) on F and H were built. Based on these models, the corresponding quantiles for the erosion magnitude D were also determined. In the multivariate case, using the 2-dimensional normal distribution, (log(D), F), (log(D), H), and (log(D), T) concentration ellipses were determined for the above pairs of parameters for probabilities of 0.9, 0.99 and 0.999, respectively. The application of one-dimensional distribution results in the lowest values of eroded material of dune, while the use of concentration ellipses estimates the highest values of dune erosion. Moreover, the developed log-linear models better predict the values of eroded material of dune along natural coast than on protected one.

Observation and modelling of infragravity waves at a large meso-tidal inlet and lagoon

The role of infragravity waves (IG waves) in beach and dune erosion or in flood hazard has been extensively studied on open beaches. In contrast, the detailed characterization of IG waves and their contribution to the Total Water Level (TWL) along the shore of inlets received little attention so far. In such environment, there is a real lack of in situ observations of waves and hydrodynamics conditions at appropriate spatial and temporal coverage to study the role of infragravity (IG) waves (long waves of frequency typically ranging between 0.004 Hz and 0.04–0.05 Hz) on coastal hazards. This contribution is based on field observations collected at the Arcachon Lagoon, a shallow semi-enclosed lagoon connected to the ocean by a large tidal inlet, located in southwest France. Analyses combine observations made at several locations during storm events within the inlet and the lagoon with numerical simulation with the XBeach surfbeat model to explore the spatial variability of IG waves and simulate observed, historical, and idealized storm conditions. The results show that IG waves are substantial during typical winter storms at the inlet and range from Hm0 = 0.8 to over 1 m across the ebb delta and about 0.4–0.6 m in the inner part of the inlet. At the lagoon entrance, IG waves remain substantial (about 0.1–0.2 m) and decrease to a few centimeters at the lagoon shore. The spatial variability and magnitude of IG waves along the inlet coast, simulated for the historical storms, are quite comparable to those observed during classical winter, and do not increase linearly with offshore wave energy. However, both observations and simulations reveal local amplifications of IG waves in the inner part of the inlet, especially along the sheltered coast were IG waves dominate the variance of free surface elevation, reaching about 0.6–0.7 m during common storms and more than 1 m for an extreme storm scenario. A numerical experiment indicates that IG wave reflection from one coast to the other contributes up to 35–40% of the measured IG wave height at a hot spot located along the sheltered coast. Finally, the contribution of IG waves to TWL at the shore on both sides of the inlet has been estimated to be about 0.4–0.6 m for a common storm and 0.6–0.9 m for an extreme scenario, locally peaking at 0.74 and 1.1 m respectively and overpassing the contribution of wave-induced setup. This work provides new insights into the contribution of IG waves to TWL and its implications for overtopping flooding hazard and overwash processes at large inlets, highlighting the need to consider IG waves in Early Warning Systems or hazard mapping for flood prevention plans in these environments.

The future of the Portuguese (SW Europe) most vulnerable coastal areas under climate change – Part II: Future extreme coastal flooding from downscaled bias corrected wave climate projections

Episodic extreme coastal flooding is considered one of the most serious threats to the global coastlines, endangering infrastructure, ecosystems, and communities. The synchronized effects of extreme wave events, storm surges and astronomical tides are particularly worrying in the context of sea level rise (SLR), and a comprehensive understanding of their future dynamics remains challenging. In this study, an innovative approach for a vulnerability assessment of sandy low-lying coastal areas, based on dynamic ensemble projections is proposed. In the current Part II study, the combined effects of future projected SLR, tides, storm surges and wave action are investigated at five key-locations along the Portuguese coastline, considering projected digital terrain models, built upon the shoreline projections obtained in Part I. Future extreme total water levels are obtained through a probabilistic approach, and extreme wave events are defined considering high wave energy thresholds in a changing climate. Overall, extreme coastal flooding is projected across several urbanized sections along the Portuguese coastline, especially in areas without artificial protection infrastructures. Dune erosion is expected along the sandy stretches, reducing the natural protection against extreme coastal events up to 13.3%, and promoting widespread overtopping, leaving populations more exposed. Future projections reveal the episodic flooding of up to 1.47 km2 of land along the 14 km of analyzed coastline, threatening households and commercial hubs, besides services and communication routes. As physical and human losses may increase substantially in the future, our results call for the implementation of adequate coastal management and adaptation plans, strategically defined to withstand changes until 2100 and beyond.

Observations on the role of internal sand moisture dynamics in wave-driven dune face erosion

Understanding and predicting dune erosion is crucial for coastal hazards mitigation, ecosystem preservation, as well as the protection of human settlements and infrastructure along sandy coastlines. However, our knowledge regarding the influence and potential importance of internal sand moisture content on wave-driven dune face erosion processes remains limited. This paper presents the findings from an extensive series of controlled wave flume experiments of eroding, unvegetated dunes, combining a range of wave conditions and water levels. A further variable that is studied directly for the first time is the internal moisture content of the dune. The initial moisture content and its evolving dynamics within the eroding dune face are quantified, revealing this to be a determining factor of the observed erosion rates, the final horizontal erosion distance, and the dune face failure type. Importantly, infiltration into the dune with each wave was not a driving mechanism of observed failures, but rather the rapid increase and then decrease of the phreatic surface within the dune, resulting in excess pore pressures and destabilization of the sediment matrix. Based on these observations two distinct mechanisms of shear failure and resulting dune face slumping are identified for unsaturated dunes corresponding to ‘minimum’ and ‘field capacity’ internal moisture content: Type 1 is associated with a circular failure surface in the absence of notching at the base of the dune, while for Type 2, notching is present and the failure surface is vertical. Under fully saturated conditions, the phreatic surface is observed to decouple from the wave runup, with excess water continuously exiting the dune face near the base. This results in rapid shear failure with no notching (Type 3). Significantly, dunes with saturated initial pore moisture content above the capillary fringe are observed to have up to 35 % greater erosion potential, consistently receding further landward than the two unsaturated counterparts as well as undergoing slumping in the absence of wave impact. A new conceptual framework is presented, comprising of a three-phase erosion sequence that directly links dune face failure mechanisms to wave runup and prevailing groundwater conditions.

Sands Through the Hourglass

Providing insights into relationships between wave activity and coastline dune erosion

Coastal processes and dune stability: Insights from wave transmission and runup modeling

Dunes not only serve as natural landscapes but also act as crucial natural barriers protecting coastlines from storm surges. However, the stability of coastlines and dunes is further affected by climate change-induced sea level rise and increased storm activity. An effective evaluation of dune stability necessitates the collection of parameters such as wave height, changes in dune crest elevation, and dune erosion rates. This research employs wave flumes and high-speed camera technology in laboratory settings to observe and simulate coastal dynamics under overwash and collision regimes. The study investigates wave propagation under both regimes using the XBeach model. In the overwash regime, the model slightly overestimates the values of infragravity waves, whereas its accuracy improved under the collision regime. Moreover, in the overwash regime, higher wave skewness results in more sediment transport to the shore, exhibiting a linear relationship between sediment erosion volume and shoreline retreat distance. Through comparison with time series wave runup data obtained by cameras and traditional predictive formulas, the study validates the applicability of the formula proposed by Stockdon as a predictive tool for wave runup in this experiment. To evaluate dune stability, the study introduces the dimensionless overwash threshold parameter Cs, which is based on wave runup and dune crest elevation, to distinguish between dunes in a collision regime or an overwash regime. These findings help identify dune stability patterns, aiding in early detection of coastal erosion and assisting authorities in ecosystem management.

Medium-Term Effects of Dune Erosion and Longshore Sediment Transport on Beach–Dune Systems Evolution

Medium-Term Effects of Dune Erosion and Longshore Sediment Transport on Beach–Dune Systems Evolution

OSL dating of very young aeolian sediments of NW Spain to assess dune erosion and accretion periods

Optically stimulated luminescence (OSL) ages of young coastal dune ridges have allowed getting more knowledge on the deposition, erosion and evolution of coastal dune systems in Northern Europe during historical times. However, there is a lack of knowledge of the evolution of the same systems in SW Europe. The studies published in the last years about fossil dunes in NW Spain have allowed the reconstruction of the coastal evolution of this area from the Marine Isotopic Stage (MIS 8) until the Middle Holocene. However, there is still a poor knowledge for the Late Holocene and namely the last centuries. Dating young sediments is challenging due to the low signal to noise ratio of the natural OSL signal and because young samples are very sensitive to thermal transfer or partial bleaching of the luminescence signal during transport. In the last century, erosion and accretion events are better known because remote sensing methods allowed to model some coastal dune systems. However, OSL dating has also been particularly useful in NW Europe to get a better knowledge on the coastal dune evolution. In this work, seven samples from dune ridges and a climbing dune of a coastal system in Playa de Trece (NW Spain) were dated by OSL, as they record the last accretion events occurred in the last two centuries, and above all the 20th Century. For assessing the ages we have compared the results from both parametric central age models and Bayesian statistic using R package BayLum.

Observing And Characterizing Infragravity Waves Through Different Sampling Devices: A Case-Study Off The Belgian Coast

Infragravity waves are surface waves with relatively longer periods in comparison to periods of the spectrum-dominant gravity waves. They are characterized by oscillations between 20 and 300 seconds (0.0033 Hz < f < 0.05 Hz), amplitudes that range from a few millimeters to tens of centimeters, and wavelengths of kilometers (Munk, 1950; Holman and Bowen, 1982; Ardhuin et al., 2014). Their forcing is linked to, amongst others, nonlinear interaction between sea swell waves, varying wave heights causing the breaking point of the waves to vary with height, and height variation of incoming waves (Bertin et al., 2018). Infragravity waves play an important role in coastal dynamics (Svendsen, 2005) and have been reported to trigger nearshore hazards such as beach and dune erosion (de Vries et al. 2008; Roelvink et al., 2009), development of seiches in harbors (Melito et al., 2006; Cuomo and Guza, 2017), wave-driven coastal inundation (Gent, 2001; Stockdon et al., 2006), and ice shelves collapsing (Bromirski et al., 2010). Therefore, revealing infragravity wave characteristics is of utmost importance to understand their potential to generate hazards in a certain region, especially at sites strongly influenced by human occupation and activities. Their consideration in coastal safety planning can avoid damages, as several locations have already experienced in the past (Yamanaka et al., 2019). Implementing optimal sampling strategies for observing and characterizing infragravity waves might be challenging. By nature, these waves are hard to measure accurately due to their low amplitude. Their evolving characteristics in an environment marked by pronounced bathymetric features, such as the sand bank systems off the Belgian coast, add a degree of complexity that requires testing of different approaches, and at different sites. Within this context, this work first revisits observational approaches, instrumentation, logistics, and sampling techniques that have been used to study this phenomenon on the Belgian Coast. The advantages, challenges and limitations of different approaches are discussed, and best practices for collecting high-quality data in the field are addressed. To do so, this study explores multi-sensor in situ deployments conducted at four selected sites off the Belgian coast (Figure 1) (Nieuwpoort, Raversijde (inshore and offshore Stroombank), and Trapegeer) within the context of the “Influence of infragravity sea waves during storms on the hydro- and morphodynamic processes along hybrid soft-hard coastal defence structures with a shallow foreshore” project, an FWO-funded initiative being conducted in collaboration between UGent, VLIZ, and KULeuven and with support of Agency for Coastal and Maritime Services (AMDK). More specifically, field observations were conducted using multipurpose mooring frames equipped both with (i) Acoustic Doppler Current Profiles (ADCPs) to sample pressure (0.1% FS), current, and sea surface elevation through acoustic surface tracking and (ii) high-accuracy quartz pressure sensors (accuracy 0.01 % FS). Both ADCPs and pressure sensors were set to measure continuously at 4 Hz being, therefore, able to capture both infra- and gravity waves. Furthermore, the moorings were collocated with standard wave buoys from AMDK. Data was collected continuously for about 3 months, covering storm and calm wave conditions. Finally, the measurements from ADCPs (pressure and acoustic) and pressure sensors were compared and used to derive the infragravity wave characteristics, as well as cross-validated against wave buoy data.

Towards Accurate Modeling Of Aboveground Vegetation In White Dunes: Biomechanics Of Marram Grass (Ammophila Arenaria)

Coastal dunes, shaped by natural processes, particularly aeolian sediment transport driven by onshore winds, are dynamic environments where vegetation plays a pivotal role in trapping sediments, enabling dunes to reach substantial heights. However, the biomechanical traits of aboveground dune vegetation have received limited attention, impeding precise modeling in coastal engineering. Understanding dune erosion and accretion is essential for enhancing coastal resilience and the integration as ecosystem-based coastal protection measures. Notably, prior research has primarily focused on salt marshes and seagrass (e.g. Keimer et al. 2023), neglecting more detailed modeling of dune vegetation, often employing simplified methods like live vegetation (Figlus et al. 2014; Silva et al. 2016) or wooden dowels (Kobayashi et al. 2013; Bryant et al. 2019). The hypothesis tested for the first time here is that geographic expositions and seasonal growth stages can be quantified for marram grass (Ammophila arenaria), and that in turn, these vegetation characteristics will inform laboratory studies involving the interaction of waves, flexible vegetation and eroding dunes.

Field observations of wave-averaged suspended sediment concentrations in the inner surf zone with varying storm conditions

During extreme conditions, the transport of the wave-averaged suspended sediment concentrations in the inner surf zone affects dune erosion. Although large-scale laboratory experiments have provided insight in what drives these sediment concentrations, corresponding field data are lacking. To fill this gap, novel field observations of suspended sediment concentrations are compared to drivers that govern sediment suspension during storm conditions known from literature. A total of 128 time intervals of 20 min are analysed, spread over 10 different high water events with different hydrodynamic conditions. For each time interval, the wave-averaged (i.e. 20 min mean) suspended sediment concentration is computed and compared to three suspension drivers. The studied drivers are (1) bed shear due to near bed velocities that originate from mean currents in combination with wave-induced orbital flow, (2) the horizontal pressure gradients under steep wave fronts that increase the forces on the bed material, and (3) bore-induced turbulence that is generated at the free surface and reaches the bed. The derived bore-induced turbulence generates the greatest correlation with the mean suspended sediment concentrations (r = 0.74, p = 4.47E-23). Samples that deviate from this correlation correspond to time intervals with lower values of derived bore turbulence, less wave energy saturation in the inner surf zone, and stronger mean currents. The correlation with the mean suspended sediment concentrations increases when the shear stress originating from mean currents is used for these time intervals (r = 0.83, p = 1.63E-33). For time intervals during which more energetic conditions persist and the wave energy is saturated in the nearshore, bore turbulence was the dominant mechanism in stirring up sediment. The outcome of this study suggests that, based on the events analysed, dune erosion models may achieve more accurate results if computations of suspended sediment concentrations include a bore-induced turbulence term, or if already included, properly address the relative importance of bore-induced turbulence when compared to bed shearing.

Observations of wave run-up affected by dune scarp during storm conditions: a two dimensional large-scaled movable bed experiment

Artificial dunes serve as essential nature-based defenses against the increasing threats posed by climate change and rising sea levels along coastal regions. However, these man-made dunes are particularly susceptible to erosion during severe storm events, necessitating careful consideration of their design for effective coastal protection. Among the myriad factors influencing artificial dune design, wave run-up stands out as a paramount concern. Not only is wave run-up crucial in assessing the extent of coastal flooding, but it also plays a significant role in shaping shoreline dynamics. During intense storm events, wave run-up amplification leads to substantial erosion of sand dunes, forming dune scarps that resemble cliffs. To address these challenges, we conducted a series of innovative two-dimensional large-scale laboratory experiments using movable beds. These experiments aimed to provide a quantitative understanding of wave run-up characteristics on dune scarps. Additionally, our study explored the feasibility of using existing empirical formulas to predict the 2% exceedance of wave run-up (referred to as R2%) in such scenarios. Our results revealed a consistent trend in R2% values, irrespective of variations in the surf similarity parameter when wave run-up was influenced by a dune scarp. Notably, our findings recommend the adoption of the Stockdon empirical formula, incorporating beach slope from the still water level to the dune scarp toe, as an effective method for predicting R2% during highly erosive conditions. This approach can significantly enhance the design and functionality of artificial dunes, bolstering their capacity to safeguard coastal areas from the impacts of severe storms and erosion, thus contributing to resilient coastal ecosystems and sustainable coastal management.

Measurements of dune erosion processes during the RealDune/REFLEX experiments

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 constructed just above the high water line to measure storm erosion and dune impacts from higher water levels and waves. During the experiment, three storms occurred that resulted in significant erosion of both dunes. The collected hydrodynamic data include pressure sensor and velocimeter data along two cross-shore transects. The collected morphodynamic data include bathymetry and topography surveys, optical backscatter sensor data in the inner surf zone, and a continuous cross-shore line-scanning lidar data set of the dune face. This comprehensive data set can be used to (1) study relevant nearshore hydrodynamic and morphodynamic processes that occur during calm conditions, moderate conditions, and storm conditions with dune erosion in the collision regime, and (2) validate existing dune erosion models.