Assessment of groundwater hydrology of the Quaternary aquifer of Lake Chad Basin

Salehi, N. (2023) Assessment of groundwater hydrology of the Quaternary aquifer of Lake Chad Basin. PhD thesis, Universitat Politècnica de Catalunya.

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Abstract

This thesis aims to enhance the conceptual model of the Lake Chad Basin's quaternary aquifer by gathering updated hydrological, geological, meteorological, and groundwater data. Objectives include analyzing natural recharge-discharge and surface-groundwater interactions and constructing a hydro-stratigraphic-based conceptual model using a water budget approach. The Chad Aquifer Formation (CAF) is one of the world's largest transboundary aquifers, spanning the entire basin, covering 2,381,000 km² in West-Central Africa. The basin consists of the Quaternary, Lower Pliocene, and Continental Terminal aquifer systems, underlain by Precambrian crystalline basement and formations of Late Cretaceous, Tertiary, and Quaternary sandy or sandstone. The quaternary aquifer, is crucial for the basin's water balance and socio-economic development. The research comprises data gathering, storage of new geo-hydrological information, and analysis of collected data using scientific publications, ground data, remote sensing, and digital files from national and international institutions. Limited data availability in the arid and semi-arid Lake Chad Basin makes this study significant. The methodology involves storing new geo-hydrological information, utilizing 430 lithological well logs to update the basin geometry, and generating a 3D description using the RockWare code. Hydro-stratigraphic units are established based on the collected data at the basin scale. Daily natural groundwater recharge in the Quaternary aquifer for the period of 2005-2014 is quantified using a numerical model (Visual Balan). The study discusses the methods and tools employed for analyzing climatic data, estimating recharge, and modeling the unsaturated zone in the Chari-Baguirmi groundwater depression. Various hydrological and geological data sources, including remote sensing platforms, are utilized. The CAF aquifer in the basin consists of different hydrogeological layers, including the upper phreatic aquifer, Upper Pliocene aquitard, and the deep confined or unconfined aquifer of the Continental Terminal. The hydrogeological system encompasses both deep confined-unconfined aquifers and a Quaternary shallow aquifer with varying hydraulic parameters. Hydraulic connectivity exists between the aquifers in the southern part and with the main rivers. The basin boundaries primarily comprise crystalline rocks. During the 2008-2011 period, the potentiometric surface indicates regional groundwater flow towards the central and northern zones of the basin. Limited data is available for the deep confined aquifer (LPli-CT), restricting the display of groundwater contours in the southern part. The groundwater level generally declines towards Lake Chad and the upper northern basin. Groundwater recharge in the Lake Chad Basin is primarily influenced by precipitation, accounting for 0% to 13% of total precipitation in the southern part and dune systems in the north. Surface water-groundwater interactions occur during flood periods in the Komadougou-Yobe and Chari Logone River systems. Discharge primarily occurs through pumping wells, with the Quaternary aquifer supplying surface water. Lake Chad operates as an in-transit hydrologically open system, removing dissolved salts. However, exchanges between the lake and the Quaternary aquifer are limited due to hydraulic aquifer connection constraints. Unsaturated zone modeling in the Chari Baguirmi depression indicates low aquifer recharge primarily affecting the upper soil layers. The research contributes to an updated conceptual model of the Chad Aquifer Formation, enhancing understanding of hydrogeology in arid and semi-arid regions with limited data. The findings have implications for groundwater management, water balance, and flow systems, benefiting decision-makers, stakeholders, and water resource managers in the Lake Chad Basin to ensure sustainable use and management of groundwater resources.

Item Type:	Thesis (PhD)
Additional Information:	Autor/s Salehi Siavashani, Nafiseh Tipus Tesi doctoral Unitat del programa de doctorat Escola Tècnica Superior d'Enginyeria de Camins, Canals i Ports de Barcelona (ETSECCPB) Altres unitats relacionades Departament d'Enginyeria Civil i Ambiental Data de la defensa 07/07/2023
Subjects:	Q Science > QE Geology
Depositing User:	José Ángel Gómez Martín
Date Deposited:	27 Oct 2023 09:44
Last Modified:	19 Mar 2024 14:57
URI:	http://eprints.imdea-agua.org:13000/id/eprint/1571

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