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Diagnosis of the Bagoé basin moisture at the semi-dry season (Sudano-Sahelien area of Ivory Coast) using the ETM + of Landsat imagery Volume 20, issue 3, juillet-août-septembre 2009

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Laboratoire des sciences et techniques de l’eau et de l’environnement (LSTEE) UFR des sciences de la terre et des ressources minières Université de Cocody 22 B.P. 582 Abidjan 22 Côte d’Ivoire, Centre universitaire de recherche et d’application en télédétection (CURAT) UFR des sciences de la terre et des ressources minières Université de Cocody 22 B.P. 801 Abidjan 22 Côte d’Ivoire

The diagnosis of the hydrous state of the Bagoé catchment area at the semi-dry season is made using Landsat ETM + images. Located in the North of Ivory Coast, this basin belongs to the large basin of the Niger River. On the images, the wet portions of rivers are discriminated and mapped using coloured compositions and moisture index calculations, giving the maps of the wet drains network at the wet period and semi-dry season. These two networks are used to constitute two series of wet drain lengths whose exploitation makes it possible to calculate drain densities per mesh of 5 km size and their classification in 4 classes. The hydrologic stability of this basin is brought about by a network of wet drains during the wet period which correspond to 69.21 % of its global hydrological network. Hence, 30.79 % of the drains of the global hydrological network would not be topographically capable of holding water. At the semi-dry season, 37.98 % of the streams of the wet drains network dry up. This drainage is a non-preferential one since all the stream orders are concerned. The arms of the rivers are separated into several portions: the portions constantly holding water, the still wet portions and/or those which are totally dry. The resulting hydrous deficit is spatially expressed by a large extension of the classes from low to very weak drain densities to the detriment of the high densities class which is absent.