These seasonal alternations influence coastal processes, with erosion in the wet season and accretion in the dry season. Wave energy is generally low because the southwest swell from the Atlantic is dissipated across the broad continental shelf. Tides are semidiurnal, and augmented as they cross the wide continental shelf: Conakry has a mean spring tide range of 3.2m.The masses of surface water in the North-Western region of Africa were classified by Berrit (1962) and seasonal distribution by Rossignol (1973)