Hydrodynamic Characterization of the Water Table of the Upper Dallol Maouri Basin (Niger)

The Dallol Maouri is a valley of an ancient tributary of the Niger River. The groundwater in this area of the upper Dallol Maouri is little known because of the weakness of the data. The purpose of this study is to make a hydrodynamic characterization of the water table of the upper dallol Maouri by piezometric approach. A piezometric monitoring network made up of 65 points (54 wells and 11 piezometers) was set up. Six (6) piezometric measurement campaigns were carried out from June 2018 to June 2021. The piezometric survey is carried out once every six months: in January and June corresponding respectively to the high and low water period. The results show that the water table is multi-layered in places with a combination of alluvial and Continental Terminal 3 (CT3) aquifers, or perched aquifers and inferoflux aquifers around permanent ponds. The flow direction of the Continental Terminal 3 (CT3) aquifer is mainly North-East/South-West. The piezometric levels are around 219 m (in the South-West part) and 281 m (in the North-East part). The hydraulic gradient varies from 0.018‰ to 1.83‰. The recharge zones are located in the outcrop zone of the aquifer and in the valleys. A lack of recharge is observed on the plateaus despite the presence of numerous permanent ponds. The recharge coefficient in 2020 is estimated at 25% of the total rainfall recorded.

Monitoring of the Physicochemical and Bacteriological Quality of the Water of the Gounti-Yéna Basin and Assessment of the Impact on the Health of the Populations

The Gounti Yéna valley is the main watercourse that divides the left bank of the city of Niamey into two unequal parts. The area of its watershed is estimated at about 62 km2. The objective of this study is on the one hand to evaluate the current state of the physico-chemical and bacteriological quality of the water of the Gounti Yéna basin and on the other hand to define the risks of water pollution and its origin in the face of the phenomenon of the rise in the water table of this basin by defining some health risks linked to these impacts. In order to properly carry out this work, we carried out a study of the evolution of the physicochemical and bacteriological parameters of the water of the Gounti Yéna basin during the period from November 2020 to October 2021, at three sampling points chosen from upstream to downstream of the basin then entomological surveys and among the health centers of the capital. The results obtained showed that the physico-chemical quality of water in the Gounti Yéna basin is influenced by climatic factors (precipitation and temperature) and anthropogenic actions. This study also highlighted the presence of faecal contamination in the water of the Gounti Yéna basin with a greater degree during the rainy season. This contamination remains worrying and constitutes a health risk causing waterborne diseases. The stagnation of the various bodies of water is also a favorable place for the development and spread of vector-borne diseases.

Influence of Re-Greening on the Infiltrability of Soils in South-Central Niger

In the Sahel, the climate and the agricultural practices are the main factors used to observe regreening process. But the extension of the latter not being uniform in the farming fields, we can suppose that there are other factors that contribute to the re-greening of certain zones and not others. The infiltrability of soils is considered as an important factor for these changes in the last decades. The influence of re-greening on the infiltrability of soils in the southern strip of Niger was studied through a comparison of zones according to the type of sandy soils (Jigawa/Rerey), siltyclay (Guiéza), silty-sandy (Hako) and clay-silty-sandy (Laka). The evaluated parameters are the texture, the infiltrability and the ecological characteristics (specific index of regeneration “SIR” and the Importance Value Index “IVI”). The main conclusions were: the soils of Niger South-Central are characterized by a sandy texture for more than 80%. The soils which are very sandy (“Jigawa”, “Rerey” and “Guieza”) are more permeable and have more trees contrary to the soil Hako and Laka. Their encrusting has the tendency to reduce the vegetation cover on the soil. The infiltration measurements indicated that the rate of initial and stationary infiltration diminishes while going down towards the South. In fact, it has been recorded a rate of 123 mm/min of initial infiltration and 87 mm/min stationary in Dan Saga on the sandy soils against 76 mm/min and 65 mm/min in Daré respectively for the initial and stationary rate. Therefore, the infiltration seems to influence the density, the SIR and the IVI of the trees from the North towards the South. Some additional work is necessary in order to determine the contribution of Farmer Managed Natural Regeneration (FMNR) in the improvement of the quality of soils and the movement of water in the superficial zones of the soil.

Groundwater Annual Dynamics in the Basins of Woro and Chago (Eastern Niger) as Affected by Seasonal Variability and Anthropic Activities

The Sahelian region is known to have extremes climatic constraints since the end of the seventies. The studied zone is characterized by an extreme spatial and temporal variability of the environmental factors, complicating the understanding of the mechanisms governing the functioning of the hydrological system in the basin. The evapotranspiration was very high (1975 mm/an), whereas the local annual rainfall was around 300 mm/year. The piezometric data showed a rise of the groundwater level during the rainy season and a decrease in the dry season. The water balance obtained using the Penman-Monteith method showed the predominance of the evapotranspiration (75% to 80% of the rainfall) on the drainage (20% to 25% of the precipitations).