The Chari-Logone watershed is the only hydrologically active part of the Lake Chad Basin (Central Africa). The Chari-Logone River and Lake Chad exchange water with the surrounding unconfined aquifers of sedimentary and crystalline rock types. In this study, the groundwater contribution to stream flow was quantified by taking advantage of a comprehensive hydrological and chemical database from the 1970s for the upper catchment, which has no equivalent to date. The study area was limited to the larger Chari catchment where the exchanges are mainly oriented from the aquifers to the stream. Upon identification of the mixing poles using end-member mixing analysis (EMMA), and a Monte Carlo inversion of a monthly mixing mass-balance model, an annual averaged base flow of 59 ± 10% of the total stream flow was estimated for 1969–1973. Then, a hydrological model accounting for baseflow and surface flow was calibrated using a 47-year-long monthly discharge time series, and the 4-years’ monthly averaged chemical data available. The simulations yielded an average baseflow of 64% of the annual discharge. The time-constant of the reservoir model (τ = 0.2 years) used to simulate the baseflow was interpreted in terms of hydraulic diffusivity, yielding a value in the order of 10¹ m² s⁻¹. This large value corresponds to a highly productive bedrock and thick sedimentary aquifers. The main contribution to the Chari stream flows is restricted to a 140,000-km² subcatchment located in the southern tropical zone, where the recharge rate reaches 72 ± 6 mm year⁻¹.

Chari-Logone流域是乍得湖盆地（中部非洲）唯一的水文活动部分。Chari-Logone河和乍得湖与周围的沉积岩和结晶岩类型的无限制含水层交换水。在这项研究中，利用1970年代之前流域的综合水文和化学数据库，定量了地下水对水流的贡献，该数据库迄今尚无等效数据。研究区域仅限于较大的Chari流域，那里的交换主要是从含水层到河流。在使用末端成员混合分析（EMMA）确定混合极点后，以及每月混合质量平衡模型的蒙特卡罗反演后，估计1969年的年平均基本流量为总流量的59±10％ 1973年。然后，使用47年的每月排放时间序列和4年的每月平均化学数据，对考虑了基流量和地表流量的水文模型进行了校准。模拟得出的平均基流为年排放量的64％。储层模型的时间常数（ 根据水力扩散率解释了用于模拟基本流量的τ = 0.2年），得出的值约为10 ¹ m ² s ^-1。这个大值对应于高产的基岩和厚的沉积含水层。对Chari流的主要贡献限于位于南部热带地区的140,000 km ²子汇水面积，该地区的补给速率达到72±6 mm年^-1。