Jim Best

Jim Best

Jim Best is a sedimentologist and fluvial geomorphologist with research interests in the dynamics of the world’s big rivers, and has conducted field work on the Jamuna, Meghna, Paraná, Paraguay, Amazon, Mekong, Mississippi and Columbia rivers. His research investigates the links between fluid flow, sediment transport and the development of bed morphology, and use of this knowledge in contemporary channel management and interpretation of ancient fluvial landscapes. He has recently published a major review paper in Nature Geoscience concerning anthropogenic stresses on the world’€™s big rivers.

Understanding Sediment Flux in the Mekong River: Geomorphology, Tropical Cyclones, Sediment Mining and Implications for Delta Stability

The Mekong River is one of the world’s great waterways, and one that holds a socio-economic significance for the tens of millions of people living in its transboundary basin. At present, the Mekong River is under pressure from a range of anthropogenic stresses, including large-scale damming, hydrological change, and downstream sediment starvation. Understanding the nature of sediment flux in the river is key to predictions of future channel change and management, and yet, like most of the world’s big rivers, reliable estimates of sediment flux are notoriously difficult to gain.

In this paper, we detail the findings of a major geomorphological study of the lower Mekong River in Cambodia in which we have employed the techniques of acoustic Doppler current profiling, terrestrial laser scanning and multibeam echo sounding, in order to gain quantitative insights into the transport of suspended and bedload sediment, as well as bank erosion, within the Mekong River. These methods permit new sediment rating curves to be developed, and illustrate: i) the significant role of tropical cyclones in driving suspended sediment flux, and their possible change in a warming climate, and ii) that at current extraction rates from sand mining, the availability of sand on the Mekong river bed is extremely limited and sand transport to the delta is therefore under threat. We highlight how these current rates of alluvial sand extraction and future decreases in alluvial transport, which will be amplified by trapping behind hydropower dams, will threaten infrastructure and communities throughout the Lower Mekong River, including the stability of the Mekong Delta. Food and water security thus demand monitoring of water and sediment flux across the drainage basin, requirements reflected in many large rivers, and calls for a global monitoring network by which to gain such data, and thereby assess the degree of anthropogenic change.

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