STELAR-S2S

Sediment Transfer and Erosion on Large Alluvial Rivers

The
Challenge

The world's largest rivers transport an estimated 19 billion tonnes of sediment each year, with a significant fraction settling in the large deltas that are home to 14% of the world's population. Most of these large deltas are under threat from rising sea levels, ground surface subsidence and declining riverine sediment supply required for delta construction.

The Mekong, the world’s third largest river delta, is home to 20 million people and a large agricultural area dominated by rice. As such, it is vital to the economy and food security of Vietnam and the region. A change in the patterns of tropical storms is threatening the future of the Mekong River delta in Vietnam, indicating a similar risk to all of the world’s major river deltas.

While measurements and projections of sea level rise and subsidence exist for many deltas, data quantifying historic changes in fluvial sediment supply are sparse, limiting our understanding of how delta building is related to climatic fluctuations.

The
Approach

Lead researchers

Project funded by

Project partners

Aalto University

Fulcrum Graphic Communications Inc

Mekong River Commission

Office of Naval Research (ONR)

Southern Institute of Water Resources Research

Stroud Water Research Center

University of Durham

University of Exeter

University of Illinois

University of Southampton

University of Washington

WWF – Greater Mekong

This three-year research project focused on the Mekong - one of the world’s great rivers. The STELAR team wished to build new insights into how morphodynamic processes interact with climate to modulate sediment transfer from source to sink.

To assess the nature and magnitude of sediment fluxes within the Mekong River, the STELAR-S2S team used a combination of coupled catchment-scale hydrological and sediment delivery modelling, field monitoring and a new morphodynamic model capable of simulating floodplain sedimentation, channel bank erosion and within-channel erosion and deposition. Field monitoring consisted of high-resolution single and multi-beam echosounder and terrestrial laser scanner surveys to quantify morphology and morphological change, acoustic Doppler current profiling to assess in-channel flow velocity, erodibility testing of bank material resistance to hydraulic erosion, and geochronology to determine spatial variations of floodplain sedimentation.

The newly-developed morphodynamic model combined a 1-D flow and sediment transport in-channel model, a 2-D flow and sediment transport floodplain flow model and a coupled bank erosion and channel migration model. This model was then implemented over a multi-decadal historical period to simulate historical sediment exchanges along the Mekong River.

The Impact

Scientists found that changes in the behaviour of cyclones mean less sediment is running into rivers upstream of the Mekong delta, starving it of the sediments needed to guard against flooding.

The findings are significant in terms of Mekong delta sustainability into the future. The sediment load is already declining as a result of upstream damming and other human impacts such as sand mining. Climate models predict that tropical cyclones will get stronger as the climate warms but storm tracks will also move further to the North-East and away from the Mekong’s catchment, exacerbating the problems of a reduced sediment supply.

The research has global implications as other major rivers such as the Ganges (India/Bangladesh), Yangtze (China) and Mississippi (USA) have catchments that are regularly struck by tropical storms.

Some 500 million people live and work in the world’s major river deltas. This study indicates that changes in storm climatology, even in the river catchments far upstream of the deltas themselves, must also be considered when evaluating their future vulnerability to sea-level rise.

The Challenge

The Approach

The Impact

Other completed research projects

The
Challenge

The
Approach