Determining sand strip characteristics using Argus video monitoring

The wind transports sand from the beach to the dunes and is therefore important for dune growth and recovery after a storm. Identifying the conditions that favour aeolian sand transport is especially important for narrow beaches, where measured long-term (seasons to years) deposition volumes on the foredune are often substantially less than the potential input from the beach. One of the most visually distinct signs of aeolian transport can be seen when relatively dry sand moves over a wet beach and organises itself to form low, slipfaceless bedforms. These features are known as sand strips. Here, we investigate the presence and characteristics of sand strips and their dependence on regional wind conditions by using a multi-year data set of video images of the Argus tower at Egmond aan Zee, The Netherlands. The dataset average wavelength and migration rate of the sand strips is 12.0 m and 1.24 m/h, respectively. Little to no relation was found between these two sand-strip characteristics and the wind velocity. The presence of these bedforms does not depend on wind velocity either, provided the wind velocity exceeds ∼8 m/s. Instead, the wind direction determines if fully-developed sand strips form, as they are seen during alongshore or almost alongshore winds only. Our observations are indicative of topographic steering of the wind by the 25-m high foredune into the alongshore direction, as sand strips move alongshore even under onshore-oblique, regional winds.