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Hydrogeological mapping of north-central Madagascar using limited data

By Jeffrey Davies


North-central Madagascar is well endowed with surface-water. Due to soil erosion and\ud pollution, rivers can no longer provide year round clean water supplies. Shallow\ud aquifers are being developed to provide sustainable rural and urban water supplies. A\ud survey of water sources located 2760 boreholes, wells, ponds and springs in the area, but\ud understanding of groundwater occurrence remains poor. The area comprises four\ud hydrogeological zones: the dry Central High Plateau with erosion surfaces underlain by\ud weathered and fractured Basement Complex aquifers ; the wet East Coast Basin\ud underlain by Cretaceous limestone, Neogene volcanic and Recent alluvial aquifers; and\ud the northern Antsiranana and the western Mahajanga Basins underlain by Karoo\ud continental and marine sedimentary and Cretaceous -Tertiary sedimentary and volcanic\ud aquifers . Thick lateritic soils mantle much of the area. As part of the 2005-8 geological\ud mapping of north-central Madagascar, hydrogeological mapping at 1:500 000 scale was\ud undertaken based on hydrogeological, geological and geomorphological data layers\ud within an Arc9 GIS format. Georeferencedgroundwater data were collated with\ud information from a weathered basement aquifer research site north of Antanarivo.\ud Experience from studies of weathered Basement Complex, Karoo, Mezo -Tertiary and\ud Quaternary aquifers on the mainland informed map content. Seven map sheets were\ud produced at a scale of 1:500 000 using the UNESCO hydrogeological legend modified to\ud show aquifer distribution. Insert maps show depth to water-table/DEM and waterquality/\ud geomorphological unit distributions. These maps were compiled for planning\ud purposes in areas of limited hydrogeological data

Year: 2009
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