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sur le développement des zones arides et semi-arides

Titre : Characterization of the Hydrogeology of the Lodwar Alluvial Aquifer System, Turkana County, Kenya

Auteur : Tanui, Florence J

Université de soutenance : University of Nairobi

Grade : Doctor of Philosophy (PhD) in Geology 2021

Résumé partiel
Drylands account for more than a third of the world’s land area and are characterized by less than 250 mm of rainfall per year. In these regions, groundwater is a strategic resource and plays a key role in economic development, especially in sub-Saharan Africa, where it is responsible for improving livelihoods. Lodwar town depends primarily on a poorly studied groundwater system for its municipal water supplies. The aim of this research was to establish the sustainability of this aquifer system through a comprehensive study of its hydrogeological characteristics, sensitivity to climate variability, and the influence of natural and anthropogenic processes, all of which are currently unknown yet critical for its sustainable management. The methods used were : detailed geological mapping and rock analysis (petrography and X-ray fluorescence) ; remote sensing (digital elevation models and vegetation cover maps) and drone mapping of Lodwar town for stream lineament analysis ; evaluation of borehole drilling datasets including yields, static water levels, water rest levels, drawdowns, transmissivities, and borehole depth ; geophysical surveys involving vertical electrical soundings for evaluation of the hydrogeological characteristics ; aquifer hydrogeochemistry of surface (river, scoop holes, water pans) and groundwater, where field measurements included pH, Temp, and EC using hand-held Combo Tester HI98129 while, turbidity, total hardness, alkalinity, Ca2+, Mg2+, Na, K+, Fe2+, Mn2+, Cl-, F-, HCO3-, SO42- and CO32- NO3-, NO2- were measured at the Water Resources Central Laboratory based standard analytical procedures. Furthermore, stable isotopic analyses of oxygen-18, deuterium and tritium in water samples was done at Elemtex Lab, United Kingdom to establish the rainfall-surface water-groundwater interactions, groundwater age and recharge sources. The multifaceted dataset was analysed using descriptive and inferential statistics, including principal component analysis (PCA), hierarchical cluster analysis (HCA), the software PHREEQC for analysis of the water chemistry data, and all together, to develop the first conceptual aquifer model for this system.

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