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Abstract

The river streams meet the sea level either by estuaries in which the ocean flows more or less far, or by deltas, large sedimentary constructions reclaimed from the sea. The coastal dynamics of estuaries and deltas is very dependent on the difference in altitude between sea level and the bottom of the riverbed at its mouth, on the sedimentary loading transported by the river at sea, on the erosive force of the tides and on the marine currents. Among these drivers, two are rapidly changing in the Anthropocene: i) The rise of sea level due to climate change or various digging engineering works, ii) The rate of sediment transported by rivers due to the multiplication of large dams or more land husbandry inside the watershed. This review paper recalls the importance of estuaries and deltas, places with high populations due to the port sites they shelter, the richness of the alluvial lands or the importance of mangroves for natural resources and biodiversity. They indicate the principles that drive their formation and evolution. They show from the literature the important changes at the mouths of major rivers during the Anthropocene. Finally, they detail the evolution of the Medjerda Delta in Tunisia, well known since antiquity. Recent studies show the speed of its construction since the Punic period and the even faster reopening of the Gulf of Utica since the construction of large dams, the recent change of land use in the river basin and the rise in sea level. They conclude with a discussion on this global trend of the invasion of estuaries and deltas by the sea.