Interactions Nature/Société et fonctionnement du littoral très anthropisé de Bretagne Sud : approche systémique à l'échelle régionale

South Brittany societies (France) are more and more concerned with coastal vulnerability. Coastal vulnerability depends on both treaths on society and coastal system' s ability to respond to numerous constraints leading to changes. Moreover, coastal system behaviour are caracterised by numerous feedbacks, including effects due to human pressure.Thus, this paper aims at assessing interrelation between natural and anthropogenic forcing factors, in order to develop a better understanding of coast behaviour and evolution in South Brittany. In such a context, fundamental data about coastal processes as well as their spatial distribution is needed. The study has focused on two areas on south Brittany Coast. The first one, the Lorient-Nord Penthièvre area, is a wave-dominated system, mainly composed of weathered rocky cliffs and beach-dune system. The second one, The Golfe du Morbihan, is a very sheltered tidal-dominated system. Geomorphological evolutions of these coastlines between 1952 and 2000 has been analysed by using numerical aerial photographs. Results clearly demonstrate human pressure on Brittany coasts has strongly increased for the last fifty years, leading to the apparition of new complex processes, in which human and natural components can hardly be isolated. A large amount of complexity, including coastal system's lagged response or space scale interfingerings, arises from these processes and should be taken into account for any coastal vulnerability assessment.