Vertical anisotropy of hydraulic conductivity in the fissured layer of hard - rock aquifers due to the geological structure of weathering profiles

Pumping tests carried out in the fissured layer of a granitic hard-rock aquifer, interpreted at the observation wells by means of the analytical solution of Neuman and at the pumping wells using that one of Gringarten show the vertical anisotropy of this layer of the aquifer; the horizontal permeability being clearly and systematically higher than the vertical permeability. These results perfectly agree with the geological observations, the fissured layer of the weathered granite profile showing the existence of many sub-horizontal fractures. It confirms dominating role, within the fissured layer, of the permeability of fractures due to the weathering process over that one of fissures with a tectonic origin.