Hydropower development plans along the Mekong River mainstream have raised serious concerns about their impacts on the Mekong Delta. For that reason, from 2013 to 2015, the Government of Vietnam, with participation from the governments of Cambodia and Laos, conducted a ‘Study on the Impacts of Mainstream Hydropower on the Mekong River’, also known as the Mekong Delta Study or MDS. The objective was to assess the fluctuations on the flow regime of the construction and operation of the mainstream cascade hydropower scheme, and the impacts due to these changes on the natural, economic and social environment in the Mekong Delta regions of Vietnam and Cambodia.

A comprehensive integrated system of models was developed by DHI as part of the Study to understand and quantify these impacts.

Download the case story highlights flyer


Twelve hydropower projects have been proposed for the Mekong River mainstream in the Lower Mekong Basin, which covers the riparian areas of Thailand, Lao People’s Democratic Republic (Laos), Cambodia and Vietnam. Construction and operation of any or all of these proposed projects could potentially have substantial and wide‐ranging socio‐economic and environmental effects in all four countries, especially in the downstream areas.


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.


Transparent and science-based tools using available knowledge base

Impact assessment in the Mekong River and the Delta with a high temporal and spatial resolution

Better understanding of cumulative impacts on biodiversity, livelihoods and the economies of the lower Mekong countries

'The results of this Study are the basis for ministries and agencies to develop prevention, mitigation and adaptation measures for the Mekong Delta in the face of impacts from the mainstream cascade hydropower development projects. The aim is to implement programs to continue monitoring developments and assessing the impact of water resources development activities upstream. The results also provide a point of reference for Vietnam and other members of the Committee during the consultation stage of Mekong mainstream hydropower projects proposals. In addition, the findings have assisted the International Mekong River Commission in completing a Study on Sustainable Management and Development of the Mekong River Basin.'

Dr. Le Duc Trung, Director General
Office of Viet Nam National Mekong Committee

About the client

Viet Nam National Mekong Committee (VNMC) is an interdisciplinary agency responsible for assisting the Prime Minister in directing and managing inter-sectoral, inter-provincial and transboundary activities in order to effectively and sustainably manage and utilise water and related resources in the Mekong Basin, including Cuu Long (the Vietnam’s Mekong Delta parts) and SeSan-Srepok river basins.

Software used

Case story - Highlights flyer

Let us help

Want to take the next step in solving your challenge?