Water contribution given by snow melting and restitution in top of a cristalline watershed at local scale: Example of the Lignon du Forez River, Massif Central, France.
Résumé
This article takes part in the study of hydrosystems interfaces, a tricky discipline in mountain hydrology, due to the inconstant behavior of the exchanges between snow, soils and substratum. The main goal is to assess the exchanges of the snow melting and its restitution in the top of a mid-mountain watershed (Lignon du Forez, Massif Central, France). The glacial heritage of the study area shows a favorable configuration for the Lignon river springs. The Northern spring seems to depend of the soil configuration and the snow accumulation of the watershed during winter. A focus has been done on the snow accumulation and the snow water equivalent, then a monitoring of infiltration, and finally its restitution at the spring. The snow accumulation and snow water equivalent mapping have been led with ground penetrating radar. This method has been used again to investigate and to map soils depths, where this soil thickness acts as an unconfined aquifer in certain years. The infiltration monitoring has been done during winter and melting time thanks to a trench dug up in the soil and set up with Time Domain Reflectometry temperature and moisture probes. This monitoring station can detect snow presence on the ground indirectly, and can give a melting speed estimation of the snow. The volume of water given by snow melting is quantified at the spring of the river, where melting flows are clearly visible in annual flows.