Abstract
Transport of beach sand to the foredune by wind is essential for dunes to grow. The aeolian sand transport rate is related to wind velocity, but wind-based models often overpredict this transport for narrow beaches (<100 m). To better predict aeolian sand transport, the fetch-based Aeolus model was developed. Here, we qualitatively test this model by comparing its transport-rate output to visual signs of aeolian transport on video imagery collected at Egmond aan Zee, the Netherlands, during a six-month winter period. The Aeolus model and the Argus images often agree on the timing of aeolian transport days, except when transport is small; that is not always visible on the Argus images. Consistent with the imagery (minimal signs of aeolian activity in strong winds), the Aeolus model sometimes predicts the actual transport to be smaller than the potential transport. This difference is largest when wind velocity is large, and its direction is cross-shore. Although transport limitations are not predicted to be common, the results suggest that their effect on the total transport in the study period was substantial. This indicates that the fetch distance should be taken into account when calculating aeolian transport for narrow beaches on longer timescales (>weeks).
Highlights
Coastal dunes are dynamic systems whose evolution is determined by aeolian and marine processes, the presence of vegetation, and human activities
How large the wind speed has to be for limited transport depends on the strength of the visual aeolian transport; a transport day with no visual sign of transport is considered limited when the wind speed is above the threshold of transport (≈8 m/s for Egmond aan Zee)
To test if the model predicts the timing and transport-limited nature of aeolian transport events correctly, its results were compared to Argus images collected during a six-month winter period at Egmond aan Zee
Summary
Coastal dunes are dynamic systems whose evolution is determined by aeolian and marine processes, the presence of vegetation, and human activities. A similar mismatch was observed by [23], who found that small wind velocities (≈8 m/s), and small potential aeolian transport rates, can cause sand strips to cover the beach. According to these studies, a short fetch, i.e., the distance over which the wind blows over the beach, and a large surface moisture content form important limitations for aeolian sand transport. Ice and snow cover form limiting factors as well [22], while nourished beaches may have reduced aeolian transport because of shell lag deposits [24]
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