The MDS was initiated by the Government of Vietnam to study the overall impact of the proposed hydropower cascade in the Mekong River mainstream on the natural, social and economic systems of the Mekong River Delta and the Tonle Sap basin. The study was intended to gather more information and build a suitable science-evidence base that will guide decision making on the Mekong mainstream hydropower development.
The Study’s approach to the impact assessment is based on internationally accepted standards, principles and experiences, such as those of the International Organization for Environmental Impact Assessment. The guidelines have been recommended by the International Organization for Environmental Impact Assessment, the United Nations Environmental Policy Law, and the World Bank’s Standard for Social Environmental Sustainability. The study also uses the best available data sources and proven scientific analysis methods to calculate and quantify impacts.
State-of-the-art hydrological, hydraulic, sediment transport, morphological and water quality modelling was used to simulate and evaluate changes likely to occur in the entire Lower Mekong Basin (LMB), if the proposed mainstream hydropower cascade were to be constructed. Model simulation output was used to assess and quantify impacts on the natural, social and economic systems of the delta and flood plains of Vietnam and Cambodia.
The modelling work was completed using MIKE Powered by DHI software (MIKE HYDRO River, MIKE HYDRO Basin and MIKE 21C) and available knowledge base to forecast both spatial and temporal changes in river flows and water quality. The MDS adopted a multi-scale modelling approach (i.e. combination of large- and small-scale models) in combination with field surveys in order to represent the general features of the LMB and also to represent details of alternative hydropower project development scenarios. For each development scenario, the output of the hydrological model consisted of multi-year time series of water flows, velocities, sediment concentrations and nutrient levels. Morphological changes, as a consequence of the erosion and sediment deposition processes, were provided in terms of changes to the longitudinal river profiles.