The document discusses the increasing risks of siltation in small reservoirs within the Nakambé basin, Burkina Faso, primarily due to soil erosion and degradation, posing a threat to water management. It highlights the need for integrated management strategies, including conservation techniques and legislation, to protect these vital resources for local communities. Key challenges include assessing the state of siltation, water quality, and developing tools for better siltation forecasting in the Volta basin.

1. H. KARAMBIR I (1) , H. YACOUBA (1) , B. BARBIER (1) , G. MAHE (2) & J-E. PATUREL (2) (1) International Institute for Water and Environmental Engineering (2iE), 01 BP 594 Ouagadougou 01 Burkina Faso, E-mail : [email_address] , Web : www.2ie-edu.org (2) HydroSciences IRD, MSE Université Montpellier 2, F-34095 Montpellier Cedex 5, France African Basins Session, IFWF3 Conference, 16 Nov 2011 From plot to basin erosion in the Sahel: an alternative method to assess siltation risks for small reservoirs in the Volta Basin

2. Background Goal and Purpose : Assess the risks of small reservoirs siltation for a better water management Location: Nakambe basin in Burkina Faso (upper part of the Volta basin) Target Groups: Local communities (farmers, fishers, breeders, others users) Approach: Upscaling soil erosion from plot to basin scale based on soils surface characteristics

3. Plot scale (1 m²) Catchment scale (37 km²) Basin scale (418 km²) Outlet Small reservoir at outlet

4. Findings / Highlights Soil erosion and degradation is significantly increasing from one year to another. This represents a serious threat for small reservoirs. The potential accumulation in the reservoir shows a loss of capacity about 12% over three years studies. A need for actions Figure 1: Evolution of soil loss by water erosion on the reservoir watershed (418 km²) for three years of study (2004, 2005 and 2006).

5. Evidence / Solutions Figure 2: A small reservoir under intensive and multiple uses (Djibo, North of Burkina Faso) Picture: H. Karambiri, 2iE A particular attention should be given to the protection of these water resources (uplands soils and water conservation techniques, no farming buffer zones, pollution control, reforestation, etc..) Integrated management of small reservoirs (resources, uses, users, consultation framework, legislation and policies, …) Small reservoirs in the Volta Basin are vital for socio-economic development of local communities, mainly in Sahelian areas under water scarcity and high spatio-temporal variability

6. Gaps / Challenges  What is the state of siltation of small reservoirs in the Volta Basin? What is the situation of water quality of small reservoirs in the Volta Basin? How to take into account the dynamics at the basin scale (land uses, socio-economic activities, agriculture, …) in assessing siltation risks (including water quality issues) of small reservoirs? Tools/methods to be developed for a better siltation forecast/prediction in small reservoirs? Hydrological inter-relations of ensemble of small reservoirs in the Volta Basin? How to integrate siltation risks in water resources management of small reservoirs?