This study describes the development, calibration and preliminary application of a dynamically coupled economic-hydrologic simulation-optimization model ensemble for evaluating the conjunctive use of surface water and groundwater in small reservoir-based irrigation systems characteristic of the Volta Basin, Africa. The focus is on a representative small reservoir irrigation system located in the Antakwidi catchment in Ghana. The model ensemble consists of the physical hydrology model Water balance Simulation Model ETH and an economic optimisation model written in General Algebraic Modeling System language. The goal of the research, conducted within the Globaler Wandel des Wasserkreislaufes Volta project, was to develop a decision support system for improving the management of land and water resources in the face of potential environmental change in the Volta Basin.