Migration of mud banks and changing coastline in French Guiana

Abstract

The French Guiana coast is characterized by migrating mud banks which act not only as markers of hydrodynamic and climatic processes but also have an important impact on coastal evolution. The role of mud banks was documented by vertical aerial photographs taken in 1979, 1982 and 1984. These allow the delineation of the intertidal parts of the banks at low tide and at identical tidal ranges. The following results were obtained: (1) Six mud banks separated by interbank eroding areas are present along the French Guiana coast. The intertidal parts of three of these banks are cut by river mouths. (2) Between 1979 and 1984 the intertidal parts of the banks migrated to the west-northwest along the coast at rates ranging from 320 to 1220 m/yr (mean rate = 900 m/yr). (3) In the same period the extent of the intertidal areas colonized by new mangroves (60 km 2) was nearly the same as that of the areas bearing older mangroves (58 km 2) that were lost by erosion, while the nature of the surface covered by the intertidal parts of the banks remained nearly the same in spite of the migration of these banks. These results suggest the existence of hydrodynamic circulation cells linked to large coastal mud banks along northeastern South America. Additionally, historical data (1955–1972) show long-term variations in the velocity of mud-bank migration.