Demonstration of strong temporary vertical circulation between wetlands and alluvial and regional aquifers

Tensiometric and piezometric values were recorded in an alluvial valley of the Seine wetland from February to November 1998. As a consequence of two f lood events, the groundwater head once rose above the soil surface. When th e water level in the Seine decreased, the vertical hydraulic gradient betwe en the underlying Senonian chalk and the alluvia increased to 16 parts per thousand. During the few days of recession the alluvial wetlands were fed b y an upward flow from the regional chalk aquifer and drained towards the ri ver through a more permeable alluvial layer (1.5 m to 7 m below soil surfac e). ((C) Academie des sciences / Elsevier, Paris.).