Spatial and vertical wind patterns in a path-induced blowout in opposing wind conditions

Blowouts are geomorphic features formed through the interplay of aeolian processes, vegetation cover and anthropogenic disturbance. Although the basic dynamics of airflow over blowouts under unidirectional winds are relatively well understood, fine-scale airflow patterns under bi-directional wind regimes remain poorly characterised. This study investigates airflow dynamics within a small trough blowout located in the coastal dune system of Canet-en-Roussillon (SE France), where foot traffic has modified the original morphology. Wind data were collected using 26 anemometers deployed across and within the blowout, capturing spatial and vertical variations during both offshore and onshore wind events. The blowout exhibits a bifurcated morphology that alters airflow asymmetrically: offshore winds are steered oblique to the shoreline and sustain acceleration along the main axis (pattern [c]), whereas onshore winds generate more parallel flow, resulting in deceleration and turbulence (pattern [a]). This contrast gives rise to distinct internal flow structures, flow bifurcation under offshore winds and widespread near-surface disturbance under onshore winds. A shallow, disturbed near-surface flow develops within the blowout, constrained vertically by blowout dimensions, and decoupled from the more coherent higher and above-blowout flows aligned with the incident wind. Peak velocities for both wind directions are observed in the constricted throat region (pattern [b]), though classic jet flow does not develop, likely due to bifurcation and throat morphological constraints. These findings highlight the sensitive coupling between blowout morphology, wind regime and anthropogenic alteration in shaping airflow behaviour within a small trough blowout.