Morphosedimentary Evolution of the Macrotidal Seine Estuary Subjected to Human Impact

Many estuaries in the world have been subjected to significant human impact since the 19th century. Natural infilling and human activities, including building of embankments, dikes and jetties have modified both the morphology of these estuaries and the distribution of sedimentary facies. The Seine, a macrotidal estuary, provides a good opportunity to study such modifications, as the latest morphosedimentary observations could be compared to old sediment maps as well as to geotechnical drilling data. In the mouth of the Seine, originally a sand/gravel system sediment distribution, has now been transformed into a muddy system. The result is a regressive sequence several meters thick. It is typically fining-up and corresponds to a shift from a distal term (pebbles, gravel, and coarse sands) at its base to a proximal term (mud and fine sands) at its top. Civil engineering works have reduced the available amount of space within the estuary, leading to an increase in the natural downstream shift of the depocenter of mud brought by winter river floods. The deposition area of the mud is today in the open marine zone, where waves and tidal currents render the balance of this process precarious.