  The present study deals with the problem of evaluation of the recharge
mechanism and the characterization of the groundwater flow system in the
basement shallow aquifer, which is one of the groundwater resource in the
semi-arid South region of Madagascar. Stable isotopes (deuterium and oxygen-18)
and tritium are used to achieve with accuracy the hydrogeological and
geochemical dynamics study. Chemical analysis is used to provide complementary
information to the investigation. A space distribution of tritium concentration
and isotopic composition in groundwater shows evidence of two opposite
categories of aquifers, which is confirmed by the chemical analysis results and
by the geological features of the study site. Some groundwater flow path
directions have been identified in the study area thanks to the tritium
concentration space distribution and the geological formation. Besides, the
groundwater recharge of the shallow aquifers in the South of Madagascar has
been characterized by the exponential mixing model.
