Observations of alongshore variability in intertidal beach development and wave conditions
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As a large part of the world population lives near sandy coasts it is vital to ensure safety from flooding and coastal erosion, which makes the understanding of coastal dynamical processes important. In the past, much research has been done on the behaviour of sandy coasts, although the processes behind alongshore variations in the bar-beach-dune system are not well understood. The bar-beach-dune coupling is a key factor to fully comprehend when considering future coastal protection. Alongshore variations in wave energy dissipation over subtidal bars can generate alongshore differences in the development and accretion of the (intertidal) beach under low-energetic wave conditions, which can lead to areas with less sediment accretion resulting in possible weaknesses in the coastal area. Therefore, possible alongshore variations in intertidal beach development during mild weather conditions need to be investigated to understand beach recovery and alongshore variation therein. To unravel the alongshore variation in morphological development of the intertidal beach in relation to the incident wave conditions, after crossing the subtidal bars during low-energetic wave conditions, a 3-week fieldwork campaign at Vejers Beach, Denmark, was set out. The changes in bathymetry/topography of the intertidal beach were observed under mild weather conditions. Incident wave conditions were measured along the low tide water level; the seaward border of the intertidal beach. The behaviour of the intertidal beach was alongshore variable during mild weather conditions in an inconsistent manner, with alongshore differences in bar migration, bar elevation change and bar height change (between two days), up to 5, 0.15 and 0.25 meter, respectively. And the maximum alongshore difference in the cross-shore position of z=0 increased from ± 9 m to ± 15 m during 8 days of low-energetic wave conditions. Furthermore, there were significant correlations between alongshore variations in bar developments and alongshore variations in wave conditions, during a period of low-energetic wave conditions. However, it is uncertain how the alongshore variations in wave conditions originate, how they changed over time and which processes were responsible for the alongshore variations in bar development. Therefore, future research, with a more enhanced instrument setting, is needed to improve the knowledge concerning possible alongshore variabilities in intertidal hydrodynamics and beach recovery.