Downwind evolution of aeolian saltation across an artificially constructed coastal berm

Knowledge of aeolian sediment dynamics over an elevated berm with an upwind topographic obstacle is rather scarce and is of utmost importance for understanding aeolian transport from beach to dunes. This study reports on a field experiment designed to carry out simultaneous measurements of wind and aeolian sediment dynamics across a human-constructed berm with a steep seaward cliff backed by a dyke. In front of the dyke, a trench is excavated to prevent aeolian sand being blown to the hinterland. Two sets of measurements were carried out, one with low-moderate (6–7 m/s) oblique onshore wind and one with high velocity winds directly onshore (12–13 m/s). Due to the irregularity of topography upwind of the berm, boundary layer flow dynamics are dramatically different and influenced the sediment dynamics locally. Maximum transport was achieved at a distance of 20 to 35 m downwind from the cliff. Downwind sediment transport was characterized with an overshoot during the oblique onshore wind event. Sand mass flux rapidly increases towards a maximum value followed by a decrease to a lower equilibrium value which was approximately half of the maximum mass flux. The evolution of the vertical flux profiles downwind caused the exponential decay rate β to increase with increasing distance further away from the cliff, until an equilibrium decay rate is achieved. The measurements presented herein show that the distribution of particle trajectories for different transport events changes similar downwind of the cliff until it is stable.

Publication year:2020

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