Avalanching of the dune face: field observations and equilibrium theory

A field experiment to study dune erosion was conducted on the Sand Engine near Kijkduin, the Netherlands, from November 7th 2021 to January 7th 2022. Two artificial unvegetated dunes were constructed near the high water line, and experienced significant erosion through avalanching during three storms. This paper aims to identify what drives dune erosion through avalanching by using the collected data and equilibrium theory. Results suggest that the cumulative volume eroded through avalanching during a single high water is positively correlated with the profile mismatch between the pre-storm profile and a ‘storm equilibrium profile’, described by a 2/3rd power law, an empirical coefficient A, and the total water level. This mismatch is quantified by calculating the area integral of the profile that is acquired when the upper 35 m of the pre-storm profile is subtracted from the upper 35 m of the equilibrium profile. Avalanching commences when this mismatch becomes larger than approximately 0, after which 1 m3/m of sediment erodes from the dune face for every 3 m3/m mismatch. In addition, during one event avalanching occurred even though the elevation of the total water level did not exceed the initial elevation of the dune toe. This implies that a total water level that exceeds the initial elevation of the dune toe is not a requisite for avalanching and a collision regime to occur, which contradicts conventional definitions of dune erosion regimes. These results have implications on risk assessment of storm conditions on dune erosion.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Coastal EngineeringEnvironmental Fluid Mechanic

The effect of wave obliquity on dune erosion: A field experiment

Storm conditions can lead to excessive dune erosion with potential floods as a consequence. Barrier islands and low-lying countries protected by dunes are especially vulnerable to dune erosion. To properly assess the risks these areas face, a clear understanding of the physical processes during dune erosion is required. One of such processes is the effect of wave obliquity on sediment transport in the surf zone. Classic dune erosion models assume that dune erosion volumes decrease under oblique wave attack, because the time-averaged cross-shore undertow decreases in magnitude and with that offshore directed sediment transport decreases (Steetzel, 1993). More recent process-based erosion models predict an increase in erosion quantities, because the generated longshore currents increase surf zone sediment concentrations, and with that offshore directed sediment transport increases (Den Heijer, 2013). The main objective of this study is to analyse the effect of wave obliquity on dune erosion through a field experiment, by quantifying the effect of the decreasing undertow but increasing alongshore current on sediment concentrations in the surf zone.Coastal EngineeringEnvironmental Fluid MechanicsCivil Engineering & Geoscience

Dune erosion during storm surges: The realdune/reflex experiment at the sand engine

Storm conditions can lead to excessive dune erosion with potential floods as a consequence. Barrier islands and low-lying countries protected by dunes are especially vulnerable to dune erosion. To properly assess the risks these areas face, a clear understanding of the physical processes during dune erosion is required.An international field experiment was conducted to study dune erosion during storm surges from November 6 2021 until January 6 2022. on the Sand Engine. During the Realdune/Reflex experiment, two prototype un-vegetated dunes of 5.5 m high and 150 m long were built just above the high waterline. Due to a different shoreline orientation and nearshore bathymetry, these dunes eroded differently during moderate storm conditions. 3 storms were captured during the campaign.This abstract presents preliminary results of morphodynamic change during these 3 storms, by means of profile changes and erosion volumes.Coastal EngineeringEnvironmental Fluid Mechanic

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.Coastal EngineeringEnvironmental Fluid Mechanic