The Central-African country of Chad, located in the Sahel-Sahara zone, faces diverse shortages of portable water. The only reliable source of water available for drinking, domestic and agricultural use in the Dababa Division is groundwater. Conventional hydro-geochemical and isotopic methodology, coupled with piezometric data, allowed investigators to identify the numerous process affecting not only water quality, but also aided them to assess its suitability for different uses. The types of groundwater encountered indicated the presence of Ca-Mg-HCO3, Na-HCO3, Cl-SO4 and Na-Ca-SO4 in descending order of abundance. The data presented in this investigation shows three processes influenced the groundwater quality; these are the alteration of silicate minerals by dissolved CO2, the cationic exchange and the evaporation phenomenon, in particular, in the piezometric depression. Additionally, to these findings, this article discussed the anthropogenic processes involved, whose effects are evident in many samples with nitrate concentrations above the WHO standards. Generally, the groundwater in the study area show signs of human contamination. Recent studies also indicate the development of cardiovascular diseases among the population of this area which are directly linked to the low total hardness (TH) values, or general softness, of the water. The groundwater in Dababa is, however, usable for agricultural and other domestic needs. Based on the calculation of Na‰ and the sodium adsorption ratio, the sampled waters are suitable for irrigation. Key words: Groundwater, World Health Organization (WHO), hydrogeochemistry, isotope, Dababa, Chad.

The demography (3.4%) and the development of anthropic activities in the city of Sarh, constitute a risk of groundwater pollution. That is why a vulnerability map is determined to contribute to the protection of groundwater resources against possible pollution for future decision and allocation of land and activities. The present study interested the city of Sarh and had the objective to elaborate a vulnerability map to pollution by applying the DRASTIC method. The data required for this study are summarized in seven critical factors specific to the model applied (depth of the water table, net recharge, aquifer lithology, soil type, topography (slope), unsaturated zone lithology and hydraulic conductivity). They were acquired from several sources and converted by the GIS into thematic maps. For each critical parameter, a coefficient and a weight were assigned according to its importance in the DRASTIC model. The resulting map shows three classes of vulnerability; 36% of the Sarh region has very low vulnerability, 35% has low vulnerability and 29% has medium vulnerability.

This study investigates the Batha endorheic basin in Chad, situated east of the Lake Chad basin in the arid to semi-arid Sahelian zone. This region has not yet undergone comprehensive geological and hydrogeological studies. More broadly, the transition zone between semi-arid and arid climates has been minimally explored. This research aims to evaluate the resources and dynamics of this multi-layered system using a combined geology-hydrogeology-hydrochemistry-isotopes approach. The multilayer system includes sedimentary layers (Quaternary, Pliocene, and Eocene) over a crystalline basement. A piezometric investigation of the system shows a general SE–NW groundwater, indicating an interconnection between all layers. Hydrochemical analyses identifies four main facies (calcium-bicarbonate, sodium-bicarbonate, sulphate-sodium, and mixed), primarily controlled by water–rock interaction with secondary influences from base-exchange and evaporation. Saturation indices indicate that these waters are close to equilibrium with the calcite-Mg phases, gaylussite and gypsum. Stable isotopes (oxygen-18 and deuterium) categorize groundwater into three groups: ancient water, recent and older meteoric water mixtures affected by evaporation, and mixtures more heavily impacted by evaporation. Tritium contents reveal three groups: current rainwater, modern water, and sub-modern water. These results indicate that ionic and isotopic differentiations cannot be strictly linked to specific layers, confirming the interconnected nature of the Batha system. The observed heterogeneity is mainly influenced by lithological and climatic variations. This study, though still limited, enhances significantly the understanding of the basin’s functioning and supports the rational exploitation of its vital resources for the Batha area’s development. Future investigations to complete the present study are highlighted.

This work aimed to contribute to knowledge improvement of the great Lake ecosystems of Chad, precisely that of the Lakes of Ounianga using bathymetric statements on water levels and the in situ analysis of physicochemical parameters of the lake’s waters. Bathymetric surveys facilitated characterization of the morphology of the bottom of the lakes with depths that vary from 0 to -27 m and 0 to -5.7 m for Yoan and Teli Lakes, respectively. With regards to water physio-chemistry, the temperature of the Teli Lake water measuring up to 0.5 m varied from 20.8 to 36°C, while that of Lake Yoan varied from 10.50 to 32.90°C, with an average of 22 and 27°C. The conductivity values oscillated between 69 and 111,700 μS/cm for the Lake Teli and 100 to 64,000 μS/cm for the Lake Yoan. This document illustrates the techniques used in the investigation of a lake whose study constitutes a wide field of continental hydrology. Key words: Ecosystem, lakes, bathymetry, physio-chemistry, Ounianga, Chad.