1. National Water Institute; University of Abomey-Calavi; 01 BP. 526 Cotonou Benin
2. Department of Geography; University of Bonn; Meckenheimer Allee 166 Bonn 53115 Germany
3. Hydrosciences Research Group; CSIR Natural Resources and the Environment; PO Box 395 Pretoria 0001 South Africa
4. Département de Physique/UFR Sciences et Technologies; Université Assane SECK de Ziguinchor; BP 523 Ziguinchor Sénégal
5. Applied Science and Technology Research Institute; 03 BP 7047 Ouagadougou 03 Burkina Faso
6. Department of Soil Science, Faculty of Agriculture; University of Abuja; Abuja 900211 Nigeria