Forecasting the evolution of nitrate contents in spring water using a lumped hydrologic model.
Résumé
Hydrologic forecasting by the use of lumped basin models has been widely practiced for many years. The transposition of this type of model to simulation of the evolution of nitrate contents in groundwater is much more recent. The principle of this modeling lies in the analysis of the existing records of precipitations, stream discharge, piezometric level, as well as nitrate contents in a spring or a borehole. Such an analysis makes it possible to establish, with a lumped hydrologic model, a balance between input data (precipitation, evapotranspiration, fertilizations) and output data (river discharge or piezometric level, nitrate content, crops needs) and also a transfer function. Once the model parameters are found, it is possible to determine the contents corresponding to various fertilizer application and climatic scenarios. The BICHE model, which was developed at the Ministry of Environment's request, thus enables continuous forecasting of the nitrate content evolution at the outlet of a drainage basin or in a borehole. This article describes the principles of the model and the case study of the springs of the Voulzie, at Provins (Seine-et-Marne department) which supply Paris with drinking water. The influence of the climatic variability is also analyzed.