Tidal flow separation at protruding beach nourishments

Radermacher, M.; Schipper, Matthieu de; Swinkels, Cilia; MacMahan, Jamie; Reniers, A.J.H.M.

doi:10.1002/2016jc011942

Cited by 18 publications

(23 citation statements)

References 33 publications

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“…Data were collected during a field campaign at the Sand Engine mega‐nourishment as a part of the MEGA‐Perturbation EXperiment in the fall of 2014 on the Delfland Coast of the Netherlands (Radermacher et al, ). Since the installment of the 21.5 million cubic meters of sand in 2011, the Sand Engine has dramatically changed shape (Stive et al, ); in 2011 it stretched 2 km in the alongshore and 1 km into the North Sea, and in 2014 it stretched 4 km alongshore and 800 m in the cross shore (Radermacher et al, ). The large‐scale morphology is considered very dynamic with observable bathymetric changes over periods of days to months.…”

Section: Methodsmentioning

confidence: 99%

Observations of Time‐Dependent Bedform Transformation in Combined Wave‐Current Flows

et al. 2018

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Although combined wave-current flows in the nearshore coastal zone are common, there are few observations of bedform response and inherent geometric scaling in combined flows. Our effort presents observations of bedform dynamics that were strongly influenced by waves, currents, and combined wave-current flow at two sampling locations separated by 60 m in the cross shore. Observations were collected in 2014 at the Sand Engine mega-nourishment on the Delfland coast of the Netherlands. The bedforms had wavelengths ranging from 14 cm to over 2 m and transformed shape and orientation within, at times, as little as 20 min and up to 6 hr. The dynamic set of observations was used to evaluate a fully unsteady description of changes in the bedform growth with the sediment transport continuity equation (Exner equation), relating changes in bedform volume to bedload sediment transport. Analysis shows that bedform volume was a function of the integrated transport rate over the bedform development time period. The bedform development time period (time lag of bedform growth/adjustment) is important for estimating changes in bedform volume. Results show that this continuity principle held for wave, current, and combined wave-current generated bedforms. Plain Language SummaryJust under the water at sandy beaches around the world there are sand ripples that form, grow, move, change, and decay. While the ripple feature is very aesthetically pleasing, it also serves the purpose of moving sand toward and away from the coast. In order for us to accurately predict coastal change, it is important to fully understand how sand ripples grow and decay in waves, currents, and combined wave-current flows. Field observations of growing and changing sand ripples in combined wave-current flows are used to validate a new analytical expression for estimating bedform growth and decay due to changes in the flow field energy.

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Section: Methodsmentioning

confidence: 99%

Observations of Time‐Dependent Bedform Transformation in Combined Wave‐Current Flows

et al. 2018

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“…The effect of episodic events on mixed wave-and-current energy systems is less well known, although recent studies at the Sand Engine in the Netherlands suggest that storm energy has a similar relationship to sediment transport in the presence of relatively weak tidal currents (<1 m/s) (Luijendijk et al, 2017) when wave-driven currents in the nearshore approach 1 m/s (Radermacher et al, 2017). Tidal currents observed near Katama (~3 m/s around the corner of Chappaquiddick Island and~2 m/s through the inlet) can be stronger than those observed at the Sand Engine (0.8 m/s), and wave-driven currents tend to be weaker owing to smaller wave angles relative to the shoreline orientation (typically 1 m/s at the Sand Engine compared with 0.2 to 0.9 m/s south of Katama Bay, depending on wave energy and direction).…”

Section: 1029/2017jc013708mentioning

confidence: 99%

Storm Impact on Morphological Evolution of a Sandy Inlet

2018

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Observations of waves, currents, and bathymetric change in shallow water (<10‐m depth) both inside and offshore of a migrating inlet with strong (2–3 m/s) tidal currents and complex nearshore bathymetry show over 2.5 m of erosion and accretion resulting from each of two hurricanes (offshore wave heights >8 m). A numerical model (Delft3D, 2DH mode) simulating waves, currents, and morphological change reproduces the observations with the inclusion of hurricane force winds and sediment transport parameters adjusted based on model‐data comparisons. For simulations of short hurricanes and longer nor'easters with identical offshore total time‐integrated wave energy, but different peak wave energies and storm durations, morphological change is correlated (R2 = 0.60) with storm intensity (total energy of the storm divided by the duration of the storm). Similarly, the erosion observed at the Sand Engine in the Netherlands is correlated with storm intensity. The observations and simulations suggest that the temporal distribution of energy in a storm event, as well as the total energy, impacts subsequent nearshore morphological change. Increased storm intensity enhances sediment transport in bathymetrically complex, mixed wave‐and‐tidal‐current energy environments, as well as at other wave‐dominated sandy beaches.

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“…Lastly, tides were neglected in our model setup. Morphologic change in the surf zone could be influenced by tide-induced water level variations (Price et al, 2013), tide-driven currents, but also other tide-induced phenomena specific for curved coasts (e.g., tidal flow separation; Radermacher et al, 2017).…”

Section: Comparison With Observations and Model Limitationsmentioning

confidence: 99%

Alongshore Variability in Crescentic Sandbar Patterns at a Strongly Curved Coast

et al. 2019

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Sandbars, submerged ridges of sand parallel to the shoreline, tend to develop crescentic patterns while migrating onshore. At straight coasts, these patterns form preferably under near‐normal waves through the generation of circulation cells in the flow field, whereas they decay under energetic oblique waves with associated intense alongshore currents. Recently, observations at a man‐made convex curved coast showed an alongshore variability in patterning that seems related to a spatiotemporal variability of the local wave angle (Sand Engine). Here, we aim to systematically explore how coastline curvature contributes to alongshore variability in crescentic pattern formation, by introducing local differences in wave angle and the resulting flow field. A nonlinear morphodynamic model was used to simulate the patterns in an initially alongshore uniform sandbar that migrates onshore along the imposed curved coast. The model was forced by a time‐invariant and time‐varying offshore wave angle. Simulations show that the presence of patterns and their growth rate relate to the local breaker angle, depending on the schematization of the offshore angle and the local coastline orientation. Growth rates decrease with increasing obliquity as both refraction‐induced reductions of the wave height as well as alongshore currents increase. Furthermore, simulations of variations in coastline curvature show that patterns may develop faster at strongly curved coasts if this curvature leads to an increase in near‐normal angles. This implies that beaches where the coastline orientation changes substantially, for example, due to km‐scale nourishments, become potentially more dangerous to swimmers due to strong currents that develop with pronounced bar patterns.

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Tidal flow separation at protruding beach nourishments

Cited by 18 publications

References 33 publications

Observations of Time‐Dependent Bedform Transformation in Combined Wave‐Current Flows

Observations of Time‐Dependent Bedform Transformation in Combined Wave‐Current Flows

Storm Impact on Morphological Evolution of a Sandy Inlet

Alongshore Variability in Crescentic Sandbar Patterns at a Strongly Curved Coast

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