Water balance of small reservoirs in the Volta basin: A case study of Boura reservoir in Burkina Faso

• Small reservoirs improve the reliability of water supplies in the remote areas.
• Small reservoirs promote diversification of agricultural activities at the locale scale.
• Small reservoirs are of the opportunities for increasing productive water use.
• Proper management of small reservoirs may enhance the sustainable agriculture.
• Water balance is a convenient tool for estimating the magnitudes of unknown fluxes.

Effective water resources development and management is crucial for sustainable economic growth and poverty reduction in many developing countries. In West Africa, large numbers of small reservoirs with volumes from 104 to 107 m3 play a considerable role in maintaining and developing activities in remote areas and in providing irrigation water for agriculture and supply water for both livestock and people. The lack of baseline data on reservoir operation hinders their optimal management. The objective of this study was to enhance the knowledge of water resources of the small reservoirs in order to improve their management in the context of multiple uses. This study was carried out on a small reservoir located in Southern Burkina Faso which was monitored for 2 years (from April 2012 to April 2014). A simple approach based on the mass conservation equation was developed for estimating reservoir fluxes. For a short hydrological monitoring period, the rainfall, evaporation and reservoir filling patterns revealed a different hydrological balance of the reservoir between these 2 years. A decrease of 32% in the annual rainfall leads to a 50% reduction in the annual runoff coefficient. The results showed that about 60% of water was lost by evaporation, whereas less than 20% of water caught in the reservoir was withdrawn for various uses. The available water resources in the studied system are largely sufficient to satisfy the current demands. There are still possibilities for developing uses of water storage and for enhancing the irrigation potential of the small reservoir. This analysis indicates that small reservoirs are under-performing. The results highlighted that estimating water fluxes in a reservoir is a central task to support water management authorities and stakeholders in operational strategies for water supply and irrigated agriculture.