Olivier Raynal

Across the coastal dunes, wind velocity and consequently sand transport is strongly controlled by the interaction between regional wind flow, vegetation cover and surface topography (topographic steering, Schwarz et al., 2020). Recently, knowledge has been improved on how winds erode, transport and deposit sand across coastal dunes, including the specific effects of vegetation and moisture as exemple (e.g Bauer et al., 2012; Hesp et al., 2015; Davidson et al., 2022). However, most of the existing studies are based on measurements collected along a single profile, thus limiting the understanding of alongshore variability and of the influence of the beach-dune profile on windblown sand pathways. The aim of this study is to address the differences on the wind flow pattern and resulting sediment transport during the same storm events at two beach-dune systems separated by only 7 km. The two field sites, which are exposed to the same ambient wind conditions, have contrasting dune profile morphologies primarily due to different human action (fixation/remobilization), allowing to discuss the impact of coastal dune management on aeolian processes.

The morphodynamics of the Leucate double-crescent bar system was studied over twenty years using bathymetric data supplemented by satellite images and video monitoring. Eleven different bar typologies were identified, mostly based on existing beach state classifications (Low-Tide Terrace, Transverse Bar and Rip, Rhythmic Bar and Beach), also including new heterogeneous typologies (TBR/LTT, RBB HP/RBB, TBR/RBB). The inner bar shows greater variability, with 10 different typologies observed, while the outer bar shows only three different typologies. Summer low-energy periods are dominated by TBR/LTT and TBR typologies, while RBB, although common throughout the year, dominates winter periods along with disrupted bar configurations. The return to less energetic periods in spring is associated with the establishment of heterogeneous typologies. The outer bar has a fairly stable position, although breaches at the embayments and slight movements of its horns can occur following particularly energetic episodes. The inner bar, on the other hand, is much more dynamic, with more common breaches at the embayments and significant cross-shore movement of the horns. Seasonal changes in bar typology do not lead to bar renewal through destruction/reconstruction. Overall, the morphological and typological characteristics of the bar system described here seem somewhat unique compared to the existing literature.

This study focuses on the dynamics of an intermittent estuary in a wave-dominated (microtidal) area, with low fluvial discharges and strong dominant offshore wind regimes. The aims are to understand the effect of these particular environmental factors in the dynamics of such estuaries. The results allow us to propose a synthetic morphodynamic model of evolution whereby opening phases are predominantly controlled by offshore winds, which have a significant influence in the northern Mediterranean. Inputs from rainfall/karst discharge and the overtopping of storm waves cause the lagoon to fill. Closing phases are controlled by the slight easterly swell which forms a berm at the inlet entrance. On occasion, major storms can also contribute to barrier opening. Nevertheless, offshore wind remains the main controlling factor allowing the surge of lagoon waters behind the beach barrier and the lowering of the berm by wind deflation. This leads to opening of the barrier due to the overflow of lagoon waters at the beach megacusp horns, thus connecting the sub-aerial beach with the inner bar system that is developed on topographically low sectors of the barrier. To the best of the authors’ knowledge, this type of estuary is not described in the literature.