Role of a fractured basement on the hydrology of a catchment.

In the rural catchment of the Maurets (Var, France), storm runoff is simula ted via two different representations. If in the representation, the soil p rofile is composed of the observed porous medium settled upon an impervious substratum, then the calculated flow does not fit the observation data. If a pervious layer of high water conductivity is inserted upon the imperviou s substratum to represent the observed fractured basement, the simulated fl ow better fits the observations. Moreover, in this case, simulations show t he large participation of old water to the stormflow, as do geochemical ana lyses of the catchment. (C) 2000 Academie des sciences / Editions scientifi ques et medicales Elsevier SAS.