Impacts des aménagements hydrauliques sur les systèmes fluviaux bas-normands depuis 2000 ans, premiers résultats d’une approche géomorphologique et géoarchéologique dans la moyenne vallée de la Seulles

Abstract

There is fragmentary knowledge of the hydrosedimentary dynamics of rivers in Normandy before and during the installation of numerous watermills dating from the Middle Ages and onwards. The rates of erosion and sedimentation that have occurred in Norman rivers over the last two millennia are poorly understood as are the anthropogenic and climatic forces which have influenced these processes. The current issue is to understand and measure the inheritances in the current functioning of rivers in order to help with their contemporary management. To provide answers, geomorphological and geoarchaeological research has been carried out in the middle of the Seulles valley. These studies highlight the effects of the hydraulic structures, particularly mills in the past floodplain dynamics. Indeed, the complete control of water flow since the Middle Ages has completely artificialized the riverbed, the channel slope and partitioned the river favouring lateral stability and overbank sedimentation. Watermill construction was accompanied locally by a simplification of the course of the Seulles as on the Heuzé site where a large part of the current course is artificial. These artificial changes to the river course and the acceleration of silt sedimentation in the floodplain since the medieval period are responsible for the establishment of the dynamic equilibrium and the hydrosedimentary forms of the current Seulles River. The end of the management of these hydraulic structures and their destruction during the last fifty years has had its effect on the natural balance of the river.