Applications of remote sensing and GIS for groundwater modelling of large semiarid areas: example of the Lake Chad Basin, Africa

Abstract Because of its large extent and the extremes of its climatic and environmental conditions, the Lake Chad Basin is an example of a region where it is extremely difficult to collect hydro(geo)logical field observations. So far, the scale and the scope to which remote sensing and GIS can assist groundwater modelling in such regions has not been fully exploited. We detail applications of remote sensing and GIS to improve groundwater modelling of the large superficial Quaternary aquifer, which covers 500 000 1cm 2 and forms the main water resource of the basin. Satellite imagery and GIS enabled us to refine the location of recharge and discharge areas. In a GIS framework, relevant maps and pertinent satellite images were analysed together with hydrogeological data. The rationale was to search and map key characteristics in the terrain that indicate groundwater discharge and recharge areas. In addition, maps and low cost satellite data, such as AVHRR and Meteosat, were used for a thorough mapping of the fluctuations of Lake Chad extent over the last three decades. Using GIS, this valuable information was implemented in a transient groundwater model, with the MODFLOW program. The model calibration was greatly improved by the use of remote sensing data

The use of remote sensing and GIS for water resources management of large semi-arid regions (a case study of the lake Chad basin, Africa)

POITIERS-BU Sciences (861942102) / SudocSudocFranceUnited KingdomFRG

Evaluation of energy potential of Municipal Solid Waste from African urban areas

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Application of Meteosat thermal data to map soil infiltrability in the central part of the Lake Chad basin, Africa

In the central part of the Lake Chad Basin, Africa, the superficial Quaternary aquifer (500,000 km2) forms the main water resource. Little is known about the aquifer recharge processes. Large piezometric depressions affect the aquifer and are still unexplained. Meteosat thermal composite data were used to infer qualitative information about time-space variations of soil moisture. Over the aquifer, Meteosat data reveal that after heavy rainfall, the piezometric depressions (Kadzell, Chari-Baguirmi) appear cooler than the surrounding areas (Manga and Harr). The interpretation is that above the depressions, rainwater accumulates at the surface and does not infiltrate deep into the ground, leading to the observed cooler ground. Accordingly, the depressions are characterized by low rainwater infiltrability, which presumably results in a small rainfall recharge. As far as we know, this is the first time that an observed surface phenomenon is directly related to the origin of some piezometric depressions

Remote sensing for groundwater modelling in large semiarid areas: Lake Chad Basin, Africa

Regional groundwater modelling studies in large semiarid\ud regions are often hampered by field data scarcity, in both\ud space and time. In such a case, remote sensing can offer\ud complementary datasets and guide further investigations\ud (e.g. Jackson 2002; Brunner et al. 2004; Schmid et al.\ud 2005). Presented here is an example of how remote\ud sensing and geographic information system (GIS) techniques\ud have helped regional groundwater modelling\ud through a better definition of groundwater recharge and\ud discharge areas, groundwater/surface water interaction,\ud and paleohydrological settings. The work focuses on the\ud Quaternary unconfined aquifer covering 500,000 km2 in\ud the central part of the Lake Chad Basin in north-central\ud Africa. It is shared between Chad, Niger, Nigeria and\ud Cameroon and provides fresh water for the majority of\ud ∼20 million inhabitants of the basin (Fig. 1). Quaternary\ud sediments form a continuous layer made up of fluviolacustrine\ud deposits and aeolian sands, isolated from\ud underlying aquifers by a thick layer of Pliocene clay.\ud The regional aridity may be illustrated by environmental\ud conditions to the north of Lake Chad where the annual\ud rainfall is lower than 200 mm and the population density\ud does not exceed 0.05 inhabitants per km2. Previous\ud reliable hydrogeological studies are few, most of them\ud dealing with the southern half of the aquifer. Regional\ud syntheses can be found, for instance, in Leblanc (2002)\ud and Gaultier (2004). The Quaternary aquifer has large\ud natural piezometric depressions, vast closed concentric\ud sinks also called ‘hollow aquifers’. Major piezometric\ud depressions have an amplitude of about 40 m and are\ud found in SE Niger, central Chad, and NE Nigeria. The\ud Quaternary aquifer interacts with the changing environment\ud (climate, surface water and human activities).\ud Understanding such a dynamic system and effective\ud management of this vast groundwater resource underpins\ud the need for a groundwater model of the Quaternary\ud aquifer. Such a model requires good spatio-temporal\ud definition of processes indicative of land surface and\ud aquifer interactions

Application of remote sensing and GIS for groundwater modelling of large semiarid areas: example of the Lake Chad Basin, Africa

Because of its large extent and the extremes of its climatic and environmental conditions, the Lake Chad Basin is an example of a region where it is extremely difficult to collect hydro(geo)logical field observations. So far, the scale and the scope to which remote sensing and GIS can assist groundwater modelling in such regions has not been fully exploited. We detail applications of remote sensing and GIS to improve groundwater modelling of the large superficial Quaternary aquifer, which covers 500 000 km2 and forms the main water resource of the basin. Satellite imagery and GIS enabled us to refine the location of recharge and discharge areas. In a GIS framework, relevant maps and pertinent satellite images were analysed together with hydrogeological data. The rationale was to search and map key characteristics in the terrain that indicate groundwater discharge and recharge areas. In addition, maps and low cost satellite data, such as AVHRR and Meteosat, were used for a thorough mapping of the fluctuations of Lake Chad extent over the last three decades. Using GIS, this valuable information was implemented in a transient groundwater model, with the MODFLOW program. The model calibration was greatly improved by the use of remote sensing data