Reducing the Vulnerability of Societies to Water Related Risks at the Basin Scale (Proceedings of the third International Symposium on Integrated Water Resources Management, Bochum, Germany, September 2006). IAHS Publ. 317, 2007, 167–172.

Integrated modelling of conjunctive use of surface and groundwater resources in a small-scale irrigation system in the Volta Basin, Africa

LUNA BHARATI¹ , CHARLES RODGERS², SERGE SHUMILOV³, MARIA PLOTNIKOVA² & PAUL VLEK²

1 International Water Management Institute (IWMI), 127, Sunil Mawatha, Pelawatte, Battaramulla, Sri Lanka

l.bharati@cgiar.org

2 Center for Development Research (ZEF), Bonn University, Walter-Flex str. 3, 53113 Bonn, Germany

3 Department of Computer Science III, Bonn University, Römerstr. 164, 53117 Bonn, Germany

Abstract The Volta Basin covers 400 000 km² of the West-African savanna. Agriculture is the dominant economic activity. Given the extremely unreliable rainfall, irrigation development is seen as an obvious strategy to increase agricultural production. Irrigation development is mainly linked to the construction of small and medium sized reservoirs. The potential use of groundwater for irrigation is a very important issue. In this study, we present an evaluation of the conjunctive use of surface and groundwater in a representative small reservoir–irrigation system. The physical processes are modelled with WaSiM-ETH. The physical boundary conditions needed for the optimization model are then passed on to the optimization model written in GAMS, which then simulates the capture and utilization of runoff in small reservoirs. Water can be withdrawn for irrigation, or stored. Irrigation water can also be pumped from the underlying aquifer, and pumping costs are modelled as proportional to the distance to the water table.

Key words decision support; groundwater resources; integrated modelling; irrigation; small reservoirs; Volta Basin