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Wave sequencing, Erosion, Accretion: Any miracle recipe for wave-dominated sandy beach morphodynamics?

09.11.2020, 13:15
MARUM Research Seminar
MARUM I, room 2070

Nadia Senechal

Sandy beaches have been studied extensively often driven by major societal issues and yet, long-term erosion of beaches (and dunes) is already a widespread phenomenon at the regional scale and global scale, and has been a major challenge for governance actors.

Shoreline evolution can be variable over a wide range of different temporal and/or spatial scales and this is especially the case for wave-dominated environments. This highly dynamic behaviour is essentially due to the fact that wave-dominated sandy coasts are characterized by low relaxation time that is a measure of the morphological inertia within the system; basically sandy coasts are dynamic systems, undergoing adjustments of form and process (termed morphodynamics) that can be very rapid (several meters within a few hours if one considers the shoreline or the dune foot). Many sandy wave-dominated environments around the world exhibit a seasonal imprint. This is particularly the case in the higher latitude and in the Northern Hemisphere where environmental factors may have a significant seasonal imprint. Periods of accretion and erosion are thus generally coupled to low- and high-energy wave conditions but the response also exhibits highly site-specific variations.

Nadia Senechal
Nadia Senechal

Storm-induced extreme waves and water-level conditions are key drivers in shoreline erosion. Single storms can result in meters of shoreline change within hours and a sequence of storms, for example during a winter-season may cause a seasonal, cumulative shoreline response. However recent studies showed that the same cumulative shoreline response (in term of magnitude) can be observed under variable ranges of winter conditions characterized by their number and/or intensity of storm events experienced during this period and that even after an extremely energetic winter, beaches can recover relatively fast. As underlined by Jimenez et al. (2011), managing erosion-induced problems will also depend on the resilience of the beach to extreme events: (i) by measuring the capability of the beach to recover (rebuild) from storm erosion or, (ii) by measuring the ability of the beach to withstand changes induced by the storm. Beach recovery is thus an important process in evaluating coastal vulnerability but recovery periods have received much less attention in the literature, being even neglected in studies evaluating the cumulative impact of storm clusters on beach erosion.

In this presentation we propose to provide recent insight in the seasonal response of an open sandy wave-dominated beach.