Abstract
Aeolian sediment transport on beaches is responsible for dune growth and/or recovery. Models predicting potential aeolian sediment transport rates often overpredict the amount of deposition on the foredune when applied to narrow (<100 m) beaches, pointing to supply limitations. Our goal is to better understand these limitations, especially in the long-term (>years) in order to improve predicted transport volumes and the timing of transport. Here, we used 8 years of Argus video images at Egmond aan Zee, The Netherlands, in combination with routine weather data to delineate 241 limited from 467 unlimited sand transport events to explore supply-limiting factors. Our research shows that the wind is more oriented to the west (shore normal) and is generally stronger for limited transport events. This indicates that the available fetch distance is often less than the critical fetch needed for unlimited transport. This is further confirmed by the timing of the transport events, as limited events often became unlimited during low tide when the beach was the widest and fetch potentially the longest. Our results help understanding the nature of aeolian sediment transport on narrow beaches, which will hopefully lead to better predictions of annual aeolian sediment transport rates.
Highlights
The sand needed for coastal dune growth primarily comes from the intertidal and supratidal beach
The null hypothesis states that the data for limited and unlimited events are from the same continuous distribution, while the alternative hypothesis is that limited and unlimited events are from different continuous distributions
The critical fetch cannot be determined with the Argus images, but an equation based on field results by [58] exists, and even though its general application is not proven, it can give an indication of typical critical fetch distances Fc for dry, sandy surfaces with a mean grain size of 200–300 μm: Fc = 4.38 ∗ U − 8.23
Summary
The sand needed for coastal dune growth primarily comes from the intertidal and supratidal beach. Transport on a natural beach is affected by, for example, the moisture content of the sand, the beach slope and the bed roughness (e.g., [2,3,10,11,12,13,14,15,16,17]) These factors cause moments of strong aeolian activity to not always coincide with moments of high wind velocities, and the other way around; moments of high potential transport based on wind velocity do not necessarily lead to high actual transport [15,18]. The effect of limiting factors on long-term (months to years) transport and dune development is unknown [26] and not properly quantified This would require long-term observations with high (hourly) temporal resolution to determine which wind events do induce high aeolian activity and which factors determine this
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