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Large River Morphodynamics

STELAR-S2S (Sediment Transfer and Erosion on Large Alluvial Rivers) is a three year research project funded by the UK NERC. Focused on the Mekong – one of the world’s great rivers – the STELAR team are building new insights into how morphodynamic processes interact with climate to modulate sediment transfer from source to sink.

Rationale

The Mekong

The Mekong

The world’s largest rivers transport ~19 billion tonnes of sediment each year, with a significant fraction being sequestered in the large deltas that are home to 14% of the world’s population. Most (>70%) of these large deltas are under threat from rising sea levels, ground surface subsidence and declining riverine sediment supply required for delta construction.

However, 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. This situation reflects the complexity of controls on river sediment loads, which include the influence of climate and land use change in upland areas, dam construction, and flood driven storage and remobilisation of sediment within the extensive floodplains that characterise the lowland reaches (“sediment transfer zones”) of the world’s major rivers.

This project will provide the first comprehensive quantification of these controls on riverine sediment fluxes for one of the world’s largest rivers (the Mekong), leading to new generic understanding of the relationships between climatic variability, fluvial processes and sediment flux to deltaic zones and the ocean.

Objectives

The overall aim of the STELAR project is to understand the importance of climatic and autogenic controls in determining the transfer of sediment from source-to-sink within a mega-river. The specific objectives are to:

  1. Develop a model of large river morphodynamics capable of simulating floodplain sedimentation, channel bank erosion and within-channel erosion and deposition.
  2. Parameterise and evaluate that model using high quality field data collected via:
    1. high-resolution surveys of the channel bed and banks to quantify alluvial roughness, bedload transport, and changes of channel morphology;
    2. geochronology to determine spatial variations of floodplain sedimentation;
    3. field and laboratory characterisation of bed and bank materials, and;
    4. measurements of in-channel flow velocity and sediment flux.
  1. Conducting fieldwork on the Mekong.

    Conducting fieldwork on the Mekong.

    Undertake basin hydrological and sediment modelling for historical flow discharges and sediment flux at the upstream limit of the study reach (the Kratie gauging station).

  2. Implement the model developed in (1) using Monte Carlo (MC) simulation, with data from (2) and (3), to simulate historical sediment exchanges within the study reach. To assess the model quality, simulated data will be compared with observations from (2).
  3. Use the model data sets, to answer key questions concerning the nature and magnitude of sediment fluxes within the Mekong River. This will allow the STELAR team to test specific hypotheses regarding the ways in which climate variability controls the transfer of sediment between source and sink.

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