Aeolian activity in foredune notches: Evidence from multiannual wind observations

Abstract

Coastal dunes are increasingly threatened by human activities and climate change, often with adverse effects on biodiversity. Excavating gaps, or notches, through densely vegetated foredunes is an increasingly adopted dynamic management measure aimed at enhancing aeolian sand transport from the beach to beyond the foredune, supporting both ecological diversity and coastal resilience. However, observational evidence of the wind conditions that support notch activity and of the influence of notch geometry on long-term sand transport remains limited. Using near-bed wind data collected from 2016 to 2023 in three geometrically distinct notches at Bloemendaal, the Netherlands, we found that these notches were active across a wide range of incident wind directions (130–150 deg; centred on the notch axis), with higher incident wind speeds required (up to 15 m/s at 10 m height) as winds became more oblique to the notch axis. Although notch geometry did not systematically affect how often notches were active over time, the results indicate that steeper deflation basin slopes increase annual sand transport through stronger slope-induced airflow acceleration. Together with previous studies, these findings suggest that notches with moderate deflation basin slopes (3–10 deg) and large widths (> 50 m) are most effective in promoting landward aeolian sand transport through the foredune.