Dynamique hydrosédimentaire du récif frangeant de l’Hermitage / La Saline (La Réunion) : processus physiques et flux sédimentaires
Published the 20 July 2009, updated the 22 July 2009
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Réunion Island University thesis - Oceanography, Sedimentology - Emmanuel Cordier - 20 of June 2007 at the GEOSCIENCES REUNION lab. (St Denis of La Réunion).
Dynamique hydrosédimentaire du récif frangeant de l’Hermitage (PDF, 15.6 Mo, in french)
Disturbances induced by the global climate change have significant impact on the coastal ecosystems, particularly in the tropical or subtropical countries already subjected to a pronounced anthropic pressure. In l’Ile de La Réunion, carbonate sand beaches erosion is identified since 1980 and can be linked to the fringing reef degradation. The fringing reef of L’Hermitage / La Saline is chosen to carry out a survey of the morphodynamic variation of carbonate beaches and to study the sedimentary dynamics within the fringing reef. Synthesis of environmental physical forcings reveals that carbonate beaches erosion is significant for open sea waves energy greater than 5.104 J.m-1.s-1. Surveys of morphodynamic variations of carbonate sand beaches show no seasonal changes, but a high correlation with frequency and intensity of extreme events. Hydrodynamics records underline the main forcings which drive the circulation in the study area. The reef circulation is organized in 5 hydrodynamic cells and is forced by the open-water wave energy propagation and distribution and the reef morphology. Minimum depths of 0,75 m on the outer reef-flat and 1,80 m in the back-reef are required to allow swell energy transfer to the shoreward. Suspended sediment concentrations and sedimentary fluxes are extrapolated showing a significant loss of material for the reef area studied. The results of this work underline the importance of fringing reef to shore protection and carbonate sand beaches durability in La Réunion. Survey and monitoring of coastal morphology, nearshore physical processes and open sea forcings, appear to be principal factors to take into account for integrated management of coastal areas.