Flood fields and aerial photographs: determination of submersion heights

Abstract

Over the centuries, the construction of several dikes has created a highly complex water circulation system in alluvial plains. The management of these ageing dikes, in particular understanding how they interact with flooding and the associated risks, is now a major consideration in land improvement work in alluvial plains. A method was drawn up to study in detail aerial flood photographs to provide information on the area covered by occasional flooding (area of water) over the whole of the dikes. This method was part of, and additional to, hydrogeomorphological studies and hydromodelling systems. It was developed in the lower Hérault valley and provided additional information about occasional flooding showing the actual role played by the dikes during the floods. It is the first stage towards flood risk management in alluvial plains.