Physico-Chemical and Isotopic (<sup>18</sup>O, <sup>2</sup>H and <sup>3</sup>H) Characterization of the Upper Dallol Maouri Watershed (Niger)

Dallol Maouri is one of the fossil valleys on left bank Niger River. Its watershed drains water from in Tahoua and Dosso regions Niger. The watercourse not continuous has areas surface accumulation (ponds) spreading infiltration. potential this area limited, with most ponds having a temporary to semi-permanent regime. Groundwater resources are, therefore, main sources withdrawal for human food, agriculture, livestock. Climate change through variation rainfall, often-anarchic multiplication catchment works (wells boreholes) agricultural activities can have impacts qualitative quantitative evolution groundwater. objective study characterize underground upper dallol physicochemical parameters use isotopes molecule (18O, 2H 3H). A total 53 samples were analyzed at laboratory Regional Directorate Hydraulics Sanitation Tillabéri (Niger) chemical 73 Radio Analysis Environment Laboratory (LRAE) National School Engineers Sfax (ENIS) Tunis isotopy. characterized by three types facies: calcium bicarbonate, magnesium nitrate chloride. groundwater 75% chloride-nitrate-calcium facies CT3/CT2 bicarbonate. results stable made it possible highlight presence four distinct groups: highly evaporated water, sheets Continental Terminal 1 2 (CT1 CT2) an isotopic cachet old table consisting two-layer system southwestern part area. very mineralized (40 μS 600 μS) slightly acidic (pH = 6.4). analysis radioactive isotope (3H) content identify recharge table. These also highlight: upward drainage zone, contribution lowland alluvial aquifers ranging 24% 84%. No structure zone reaches Intercalaire Hamadien, depth which estimated average m. relationship between 18O 3H contents shows two tritium higher than TU lower (CT3). recent recharges level outcrop CT3. There no hydraulic continuity plateau