Understanding how hydrosystems function is a crucial point in the current context of the new water policy implementation (European Water Framework Directive). This policy aims at ensuring both the sustainable development and the protection of human lives and goods. In this context, the challenge is to acquire and provide scientific knowledge to be used for the management of water resources and risks (drought and floods) along with the assessment of human impacts on water regime and quality. Increasing human control over rural areas increases the general vulnerability of our environment to extreme events. Evaluating the risks requires observation of hydrological and biogeochemical processes on a long term basis and at different scales that are from the plot to the basin scale. The project is based on the monitoring of a set of embedded watersheds of the Parisian Basin, representative of watersheds over limestone. The aim of this research project is to 1) provide forecast for the prevention of hydrological risks such as floods or low flows, and to 2) better understand and represent water and pollutant fluxes and transfers.