CFD simulations of wind flow across scarped foredunes: Implications for sediment pathways and beach–dune recovery after storms

Beach–dune systems are dynamic geomorphic environments subject to erosion during storms and reconstruction during swell‐dominated inter‐storm periods. Wave‐cut scarps are frequently carved into the beach–dune profile, occasionally eroding the stoss slope of the foredune. Although the rapid phases of...

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Bibliographic Details
Published in:Earth surface processes and landforms Vol. 47; no. 12; pp. 2989 - 3015
Main Authors: Bauer, Bernard O., Wakes, Sarah J.
Format: Journal Article
Language:English
Published: Bognor Regis Wiley Subscription Services, Inc 30.09.2022
Subjects:
Beach erosion
Beaches
beach–dune interaction
CFD simulations
Computer applications
Dunes
Echoes
Eolian processes
Escarpments
Flow distribution
flow dynamics over foredunes
Flow pattern
Fluid flow
Geomorphology
Healing
Kinetic energy
Mathematical models
Modelling
Offshore
Ramps
Recovery
Sand
sand ramp development
scarp healing
Slopes
Storms
Transportation systems
Turbulence
Vertical profiles
Vortices
Wind flow
Wind speed
Yields
ISSN:0197-9337, 1096-9837
Online Access:Get full text
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Summary:Beach–dune systems are dynamic geomorphic environments subject to erosion during storms and reconstruction during swell‐dominated inter‐storm periods. Wave‐cut scarps are frequently carved into the beach–dune profile, occasionally eroding the stoss slope of the foredune. Although the rapid phases of erosion have been researched and modelled extensively, relatively little is known about beach–dune recovery, especially scarp healing by aeolian processes. Computational fluid dynamic (CFD) modelling was deployed in this study to yield insights into different flow patterns across beach–dune profiles with three model foredunes (unscarped, 1 m scarp, 2 m scarp) for varying wind approach angles (α = 0–45°). The results show that the presence of a scarp substantially modifies the flow dynamics on the backbeach in front of the foredune. Vertical profiles of turbulence kinetic energy indicate that the influence of this flow‐modified zone extends out to about −7h from the scarp base (where h is the scarp height). The reduction in onshore wind speed that is characteristic of this flow‐modified zone favours sand deposition on the backbeach and sand ramp development at the base of the scarp. Shore‐normal wind approach angles yield discontinuous roller‐like vortices with reversing (offshore) flow components at the sand surface, accompanied by the evolution of echo dunes. Oblique wind approach angles yield corkscrew (helicoidal) vortices that lead to the formation of continuous sand ramps alongshore. A conceptual model of scarp healing based on ideas previously discussed in the literature and enhanced by the CFD simulation results highlights the importance of sand ramps for reconnecting the transport system on the beach to the foredune stoss slope, thereby facilitating foredune growth and maintenance. Wave‐cut scarps pose significant barriers to landward transport of sediment from the beach to the foredune because of the development of recirculating vortices at the scarp base, as shown by CFD simulations. Echo dunes form at the scarp base when wind approach angle is shore normal, but when wind is oblique, sand ramps evolve that infill and ‘heal’ the scarp. Sediment delivery to the stoss slope is enabled when sand ramps reconnect the backbeach to the foredune.
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ISSN:0197-9337
1096-9837
DOI:10.1002/esp.5439