Aeolian sand transport over complex intertidal bar-trough beach topography

• Published in: Geomorphology (Amsterdam) Vol. 105; no. 1; pp. 95 - 105
• Main Authors: Anthony, Edward J., Ruz, Marie-Hélène, Vanhée, Stéphane
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 01.04.2009; Elsevier
• Subjects: Aeolian fetch; Aeolian transport; Beach surface moisture; Earth sciences; Earth, ocean, space; Exact sciences and technology; Geomorphology, landform evolution; Intertidal bar-trough topography; Marine and continental quaternary; Surficial geology; Wind flow; Europe; Atlantic Ocean; Northeast Atlantic; North Atlantic; North Sea; France; Nord France; Western Europe; Intertidal bar-trough topography; Beach surface moisture; Aeolian transport; Wind flow; Aeolian fetch; experimental studies; boundary layer; beaches; acceleration; eolian sedimentation; dunes; modern; winds; eolian features; onshore; models; wind transport; soil moisture; morphology; topography; bars; intertidal environment; offshore; saltation; bedforms; sand; landform evolution
• ISSN: 0169-555X; 1872-695X
• DOI: 10.1016/j.geomorph.2007.12.013

Aeolian sand transport on macrotidal beaches with complex intertidal bar-trough topography (ridge-and-runnel beaches) was assessed from experiments in northern France that involved measurements of wind speed, saltation, surface moisture contents, and rates of sand trapping across surveyed portions of the upper beach profile. Beaches exhibiting intertidal bars and troughs are much more complex, topographically, than simple reflective or dissipative beaches. Furthermore, the intertidal bar-trough morphology commonly exhibits strong cross-shore variations in the moisture contents of the beach surface and in patterns of bedform development. The results of four 30-minute experiments, conducted along topographically surveyed portions of the upper beach-dune toe profile, show that troughs act as extremely efficient sand interceptors, because of their permanently saturated state, which also inhibits sand mobilisation. Troughs, thus, limit or segment the dry fetch during conditions of intermittent saltation. Flow lines, inferred from the wind profiles, suggest that complex interactions at the boundary layer are generated by the bar-trough topography. Troughs systematically appear to be characterised by air expansion, while bar faces generate ramp wind acceleration for onshore winds, and sometimes immediate downwind deceleration for offshore winds. These effects may also contribute to cross-shore variations in the rates of sand trapping. Finally, a simple conceptual model of effective fetch development, integrating the effects of the spring-neap tidal range and of gross bar-trough morphological variability over time, is proposed for bar-trough beaches. The model highlights the key theme of fetch segmentation induced by cross-shore differentiation in the moisture contents of the beach surface hinged on the complex topography of multiple bars and troughs.