Géodynamique d'un hydrosystème tropical peu anthropisé, le bassin supérieur du Niger et son delta intérieur

Abstract : This work deals with the water quality assessment of large rivers in the world, and especially with tropical rivers. Trough the monitoring of water discharge, suspended and dissolved matter fluxes over a seven year period (1991 to 1998), this study shows the specific processes occurring in the two parts of the studied watershed : the upper Niger river, and his inland delta, a very large flood-plain.
The study of water discharge on the upper watershed shows that the monitoring period is contrasted and representative of the hydrological fluctuations over the 25 years of drought. The temporal and spatial variability of suspended matter exported to the inland delta also permits to propose a simple modelling of processes involved. The water quality study shows that the river Niger and its tributaries have very low concentrations of dissolved major and trace elements. At a global scale, the weakness of annual runoff, lithology (silicate rocks), and low basin relief are the principal factors explaining the low mechanical and chemical rates observed. The results confirm that the chemical pollution of the Niger river in Mali is currently low.
Estimation of water, sediment and dissolved discharge inputs and outputs through the inland delta proves that this zone plays an important role in the water balance (30 to 45% of input is lost) and for the fluvial deposits (they amount to 26 à 54 % of input for suspended matter and to about 30% for dissolved matter). These rates are directly or indirectly linked to the spatial and temporal variability of the inundation. This variability regulates the importance of complex processes occurring in the inland delta. This work also confirms that two zones must be distinguished in the functioning of the delta, a upper part witch is specifically a deltaic zone, and a lower part witch has a particular morphology with inundation of lesser extent. Differences between these two zones are particularly evidenced for high magnitude annual flood stages.
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Submitted on : Thursday, June 3, 2004 - 1:07:36 PM
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Cécile Picouet. Géodynamique d'un hydrosystème tropical peu anthropisé, le bassin supérieur du Niger et son delta intérieur. Hydrologie. Université Montpellier II - Sciences et Techniques du Languedoc, 1999. Français. ⟨tel-00006189⟩

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