COMPARISON OF THE HYDRODYNAMIC AND STRUCTURAL CHARACTERISTICS OF THE CHALK AQUIFER OF THE NORD PAS-DE-CALAIS SHORELINE

A continuous series from the Cenomanian to the Senonian constitutes th e chalk aquifer on the Nord Pas-de-Calais coast. Although it presents a homogeneous facies, it is affected by a fracture network. A piezomet ric map established from a field study between the south of the Bouton niere du Boulonnais and the north of the Authie, and in high ground-wa ter level period (April 1995), enables one to modelize the groundwater flows. The hydraulic conductivity values obtained by this method vary in the range of 10(-3) to 10(-9) m.s(-1) on a relatively small area ( approximately 500 km(2)). Furthermore, the structural map built with t he help of well log data, allows to define hydrogeological compartment s delimited by faults, each block having different hydrodynamic behavi ours. Thus, the superposition of the results issued from the calibrati on of the model and from the interpretation of the stratigraphic data proves that the chalk aquifer can no longer be considered as homogeneo us but comprises a puzzle of juxtaposing blacks of differentiated hydr aulic properties. Structural informations may now be considered as a m ean of a partial indirect identification of the behaviour of the chalk aquifer.