François Sabatier

Coastal boulders in Martigues, French Mediterranean: evidence for extreme storm waves during the Little Ice Age

Summary. Boulder accumulations occur along a stretch of rocky coast of about 1.5 km near the French Mediterranean city of Martigues. The boulders occur up to 100 m inland from the present shoreline and some contain marine bio-constructions that are proof of residence in a subtidal or intertidal setting. The setting, spatial distribution and morphologic characteristics of these boulders indicate that they were detached from the rocky shore platform and transported landward by high-energy waves. The size, position and distance from the shoreline of 1475 boulders were measured in order to determine their volume and mass, as well as the conditions under which they were transported landward to their present positions. The results were then statistically analyzed and confronted with hydrodynamic models commonly used to evaluate the charactestics of the transporting waves. The wave characteristics thus obtained were compared to recorded and modeled extreme waves in the region. Dating of the boulders shows age ranges that correspond to the Little Ice Age (LIA), thus suggesting a relationship between their deposition and the high storm frequency that characterized the LIA. The results also indicate little likelihood of a tsunami origin for these boulders, although there is historical evidence of tsunamis in this region. The study insists on the potential for storm

The Sand Spits of the Rhône River Delta: Formation, Dynamics, Sediment Budgets and Management

This chapter describes the morphology and dynamics of the three sand spits flanking the Rhone river delta: Gracieuse, Beauduc and Espiguette spits. The formation and distal extension of these spits (respectively +5, +10–15, +10–15 m/year) results from active wave-induced longshore transport that generates sand migration downdrift from erosional updrift sectors. These erosional sectors are systematically associated with former delta distributary mouths that are being reworked by waves. In other words, the sand brought down to the sea by the Rhone participates in the construction of sand spits only following mouth abandonment. Finally, as a result of the curvature of these spits, the overall aeolian regime induces sand migration seaward in the southern sectors of the spits near the transition zone between eroding and accreting sectors. Understanding these functional aspects of spit formation and growth is important in terms of management of the Rhone delta shoreline and its sediment budget by public authorities.

Coastal Stabilization Practice in France

The expansion of coastal urban fronts, leisure ports and tourism in the course of the twentieth century has been the main driver of large-scale modification of the coastal zone in France. The development pressures generated by mass tourism and the economic boom of the 1960s have had their strongest effects in the Mediterranean, but pressures have also been important on the coast of Normandy and Picardy. In the Mediterranean, where large-scale planned development involving joint state and private capital ventures was implemented, this situation has, in many cases, exacerbated coastal instability, while endangering coastal ecosystems, and the growth of urban fronts has commonly led to a drastic reduction in beach width and to dune degradation. Coastal sediment budgets have also been seriously affected by updrift stabilization of cliffs and beaches, especially in Normandy and Picardy. In France, some of the causes of, and the responses to, shoreline destabilization have been essentially a matter of ‘hard’ engineering, for both historical and cultural reasons, although the situation has been changing over the past decade. A brief overview of shoreline stabilization procedures and structures highlights the overwhelming predominance of seawalls and groynes. Recent practices have tended to move closer to beach nourishment, which is gaining ground in France.

Modélisation du potentiel de transport sédimentaire longitudinal des plages du Languedoc-Roussillon

Résumé : Une approche modélisatrice du transport longitudinal le long des plages du LanguedocRoussillon est proposée sur la base du modèle numérique Unibest-LT (Uniform Beach Sediment Transport) en utilisant en entrée des données de houle de 1979 à 2010 (base de données ANEMOC-2) ainsi que des relevés topo-bathymétriques à haute résolution (LiDAR). Unibest-LT permet de calculer le Transport Sédimentaire Longitudinal annuel Résultant (TSLR) sur l’ensemble du linéaire côtier étudié. Les directions du TSLR modélisé concordent bien avec celles définies empiriquement et nos travaux précisent et/ou dévoilent des dérives littorales potentielles unidirectionnelles ou bidirectionnelles selon les secteurs. Mots-clés : Dérive littorale, Plages sableuses, Unibest-LT.