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See detailCharacterization of recharge mechanisms in a Precambrian basement aquifer in semi-arid south-west Niger
Abdou Babaye, Maman Sani ULiege; Orban, Philippe ULiege; Ousmane, Boureisma et al

in Hydrogeology Journal (2019)

In the central part of the semi-arid Dargol Basin of southwestern Niger, most of the groundwater resource is contained in the fractured aquifers of the Precambrian basement. The groundwater resource is ... [more ▼]

In the central part of the semi-arid Dargol Basin of southwestern Niger, most of the groundwater resource is contained in the fractured aquifers of the Precambrian basement. The groundwater resource is poorly characterized and this study is the first attempt to better describe the recharge mechanisms and hydrogeochemical behaviour of the aquifers. Hydrogeochemical and piezometric methods were combined to determine changes in recharge rate and origin of groundwaters for the shallow weathered aquifer and the deep fissured/fractured aquifer. At the basin scale, the groundwater fluxes towards the Niger River are influenced mainly by topography, with no visual long-term trend in groundwater levels (1980-2009). The hydro-geochemical signature is dominated by the calcic-bicarbonate to magnesian (70%) type. It shows evolution from an open environment with CO2 and low mineralized water (granitoids, alterites) towards a more confined environment with more mineralized waters (schists). Stable water isotopes (δ18O, δ2H) analysis suggests two main groundwater recharge mechanisms: (i) direct recharge with nearly no post-rainfall fractionation signature and (ii) indirect recharge from evaporated surface waters and/or stream-channel beds. Groundwater tritium content indicates that recharge is mostly recent, with an age less than 50 years (3H > 3 TU), with only 10% indicating low or even no recharge for the past decades. A median value of the groundwater renewal rate estimated from individual values of tritium is equivalent to 1.3% y-1, close to the one determined for groundwater samples dating to the early 1980s, thus indicating no measurable long-term change. [less ▲]

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See detailEvaluation des ressources en eau souterraine dans le bassin de Dargol (Liptako - Niger)
Abdou Babaye, Maman Sani ULiege

Doctoral thesis (2012)

Located in the southwestern part of Niger, the Dargol basin belongs to the region of Precambrian Liptako. In this area, most of the groundwater resources are stored in fractured aquifers of Precambrian ... [more ▼]

Located in the southwestern part of Niger, the Dargol basin belongs to the region of Precambrian Liptako. In this area, most of the groundwater resources are stored in fractured aquifers of Precambrian basement. Since the late 1980s, major rural water supply programs were interested in these aquifers and thousands of boreholes were drilled to cover the water needs of the growing population. However, many of them dry up during the dry season, forcing villagers to walk kilometers to fetch water their families. To increase the success rate of drilling, it is important to improve the knowledge on the functioning of these aquifers. The present study is carried out in this context. Its main objective is to identify and characterize fractured reservoirs in order to quantify and improve groundwater resources management methods of in semi-arid. A multidisciplinary methodology is developed to achieve this goal. Its combines lineaments maps, major element geochemistry and isotopic analyzes of drill logs. The lineaments cartography are made from the satellite imagery analysis. It is completed by field measurements, geological and geophysical data analysis. This study helped to understand the influence of the directions of fractures in the yield of the boreholes. New field investigations, particularly piezometric measurements, analyze of water and structural measurements were performed. The chemistry of water in this area revealed three sources of main ions which are from entropic origins, dissolution of gypsum and weathering of silicates minerals. Approximately 19% of boreholes recorded a high content of nitrates exceeding WHO standards (50 mg / l). To better understand the modes of recharge of these fissured aquifers, isotopic approaches were used. Stable isotope ratios (δ18O, δ2H) indicate two groundwater recharge mechanisms: direct recharge waters with little or no rain evaporated and indirect recharge which are infiltration surface water and water from stream channels beds. The analysis of the tritium content of the water indicates that recharge is new at most of the points investigated. In contrast, in area of low levels of tritium, the renewal rate appears to be low or even zero. On the basis of these data, a multi-criteria analysis was performed to produce maps of potential recharge areas and productivity index. These maps are validated using independent data and can be used as a pragmatic tool for water resources management and for future surveys. [less ▲]

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See detailEvaluation qualitative et quantitative des ressources en eau souterraine dasn le bassin de Dargol (Liptako – Niger)
Abdou Babaye, Maman Sani ULiege; Boureimane, Ousmane; Orban, Philippe ULiege et al

Conference (2012, November)

Située dans la partie Sud-Ouest du Niger, le bassin de Dargol appartient à la région de socle précambrien du Liptako. L’étude du chimisme des eaux souterraines révèle trois types de faciès dont le plus ... [more ▼]

Située dans la partie Sud-Ouest du Niger, le bassin de Dargol appartient à la région de socle précambrien du Liptako. L’étude du chimisme des eaux souterraines révèle trois types de faciès dont le plus dominant est le type bicarbonaté calcique à magnésien (65%). Environ 47% d’ouvrages ont des teneurs en nitrates dépassant largement les normes OMS (50 mg/l). Les teneurs en isotopes stables (δ18O, δ2H) de la nappe indiquent deux mécanismes de recharge: une recharge directe par les eaux des pluies peu ou pas évaporées, et une recharge indirecte par les eaux évaporées issues des lits de koris et des eaux de surface. L’analyse des teneurs en tritium de la nappe indique que la recharge est récente pour la majorité des points investigués. En revanche, dans le secteur à faibles teneurs en tritium, le taux de renouvellement semble être faible voire nul. [less ▲]

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