One of the major problems in hydrogeology investigations of arid and semi-arid regions is the
determination of water that contributed to the recharge of the water table. By considering the hydrodynamic
characteristics of the Quaternary aquifers in the Southern sector of the Lake Chad basin, this study has
permitted to obtain a quantitative evaluation of the groundwater resources available in a selected area of about
4000 km . The estimated regulating reserve ranges between 0.1 to 0.5 x 10 m /year. Monthly and yearly 2 9 3
estimation of the water budget, for a period of 16 years, according to the Thornthwaite-Mather method, shows
that the main source of regulating reserve is the August rain. For a dry water year (like 1984), there is no
effective rainfall, while in a year with a favourable rainfall, for example, we could have effective rainfall ranging
between 10 and 15% that could improve the groundwater recharge.