The Var is a coastal river in the south-east of France flowing into the Mediterranean Sea after sinking in the two departments of Alpes-de-Haute-Provence and Alpes-Maritimes. It is the main watershed of the Alpes-Maritimes, with a large area of ​​2822 km². Its source is Estenc, a hamlet of the municipality of Entraunes, located at an altitude of 1,790 meters. Its 125 km course ends between Nice and Saint-Laurent-du-Var. Its geological ensemble is characterized by metamorphic and schistose formations. The Var receives, near its source, the waters of the torrents of Colombier and Jallorgues to which the small streams descendants of the col Cayolle are added further downstream.

   The basin is characterised by altitudes ranging from 0 m on the coast to more than 3000 m on the ridge line that separates France from Italy (Figure 1: Geoman 1997). Its dimensions reach 70 km for the east / west axis and 75 km for the north / south route. The morphology of the basin is marked by the high values ​​of the slopes which locally exceed 20% its compactness. The hydrographic network is organized around four large valleys which generate in addition to the Var the tributaries that are Tinée, the Vesubie and the Estéron.

   The basin of the Var is characterised by a very strong geological heterogeneity. Four main training families can be identified:

  • a large crystalline and metamorphic zone around the reliefs of the Argentera-Mercantour massif. Outcrops of these formations occupy the eastern part of the watershed;
  • Mesozoic and Cenozoic successions of the arc of Castellane, which are represented on the one hand by calcareous and marl-limestone series as well as by the Annot sandstones (south / east of the basin);
  • Permian estates, mostly pelitic (central watershed);
  • Pliocene formations gather pudding and blue marl (low valley of the Var).

   These geologies support soils with a characteristic of being thin and rapidly saturated during precipitation. The runoff process is favoured.