The Addos mountain stream (torrent in French) is 4 kilometres long. A mountain stream is a natural water course located in the mountains. The flow regime is characterised by a steep gradient, with a very fast and therefore turbulent water flow producing significant erosion. It is also defined by a significant variation in flow rate depending on precipitation levels. In this mountain stream, as in many others, numerous small sills (small dams) have been created to slow down the water flow and limit the impact of floods.