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Alexandre Dubois (PhD)

Alexandre Dubois


Thesis defended in 2012
in Lorient
Physical Geography

Morphodynamic behaviour of pocket beaches in a semi-sheltered meso-tidal environment : example of the Southern beaches of the Rhuys peninsula, Southern Brittany


Pocket beaches take place along the rocky coastlines. On the Rhuys peninsula, they form protecting sandy barriers at the back low wetlands partially connected to the marine environment. These beaches undergo a strong meso-tidal range, when they are located behind a structural barrier, the ocean swell is strongly attenuated. The local wind generates an important sea of wind whose short frequency waves thus created favour the greatest transverse morphological change and the greatest longitudinal sediment transport. The various hydrodynamic and topographic experiments carried out in the field have highlighted longitudinal sediment transport favoured by a moderate and persistent local wind. With greater agitation, the sedimentary transfers are carried out transversally by more powerful processes of surfing and bank jet. Exchanges take place around a point of equilibrium of lesser activity. Wind and swell have a heterogeneous impact in space. Moreover, the variations in volume clearly indicate that each beach system is independent. No exchange of sediment between beaches is demonstrated, whereas a connection is allowed with the near subtidal domain, between rocky flats. Finally, the degree of impact of a storm depends on its trajectory and the water level. Moreover, the eroded volume is quickly recovered by the system. The sediment budget is preserved. However, with the rise in sea level, dune belts can break with an expected longitudinal redistribution.

David Menier

Transversal sand dynamics
Meso-tidal range
Rhuys peninsula