Calcul de la recharge naturelle par la méthode de fluctuation de la nappe aquifère: où implanter un puits d’observation

Accurate evaluation of natural recharge is fundamental for the estimation of renewable groundwater resources and constitutes a key issue for water resources management. Among physical, chemical and numerical methods, the water-table fluctuation technique is simple and easy to use. The main question is where, with respect to the draining stream, to locate the monitoring well to effectively observe representative water level fluctuations. Storage and discharged volumes in an unconfined aquifer during the water-table fluctuation application are described with equations using the Dupuit-Forchheimer model. This leads to the determination of an optimal distance from the stream (0.4 times the length of the aquifer) for siting observation wells. Beyond this distance, the computed volumes stored in the aquifer are overestimated by up to 20%. Less than this distance, the stored volume is highly underestimated.