Influence of dam operation on water resources management under different scenarios in the Zambezi River Basin considering environmental objectives and hydropower

Worldwide, almost 50,000 dams over 15 m height have been built during the last six decades with an aggregated storage capacity of 6,000 km3. The fact that large dams, by increasing irrigation and hydroelectricity production, can sustain development and reduce poverty has led developing countries to undertake major investment in dam construction. However, scientific progress is required in order to design and manage the future complex hydrologic/hydraulic systems in sustainable ways. The African Dams project (ADAPT) aimed at enhancing the scientific basis of integrated water resource management. New models for the real-time control and multi- objective optimization of large hydraulic structures were created and data resources enhanced through field survey. The case study considered to apply this new knowledge is the Zambezi River basin located in southern Africa. It contains many of southern Africa’s largest and most intact freshwater and estuarine wetlands, e. g. the Kafue flats, the Mana Pools and the Zambezi delta as well as several free-flowing yet unprotected river reaches. Three of Africa’s largest dams (Kariba, Cahora Bassa and Kafue) inundate hundreds of square kilometers of river habitat and modify the natural flow patterns that sustain floodplains. Increasing human activity by cities and industry is causing a regional energy shortage, leading governments and investors to plan yet more dams in the basin. In the framework of the ADAPT project, the major contribution of the present research is to set-up a hydrologic-hydraulic model of the whole catchment area which includes all relevant elements as hydraulic structures and schemes as well as floodplains. The multi- objective modelling and simulation define how dam operation can be adapted to get the highest environmental results under highest energy production. Three main steps structure the project: (1) the evaluation of the quality of available input data, (2) the definition of the specific hydrological processes needed for hydraulic-hydrological modeling of the Zambezi Basin along with the establishment of a calibration outline, (3) the assessment of the impacts of the planned new hydraulic structures and the refurbishment of the existing hydropower plants on the flow regime at critical points of the basin. At first, three operational and acknowledged satellite derived precipitation products (the Tropical Rainfall Measuring Mission product 3B42 -TRMM 3B42-, the Famine Early Warning System product 2.0 -FEWS RFE2.0- and the National Oceanic and Atmospheric Administration/Climate Prediction Centre (NOAA/CPC) morphing technique -CMORPH-) are analyzed in terms of spatial and temporal distribution of the precipitation. They are compared to ground data at daily, 10-daily and monthly time steps. Based on the results, TRMM 3B42 was chosen as input data for the hydrological modeling. Secondly, the Soil and Water Assessment Tool (SWAT 2009), a semi-distributed physically based continuous time model