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Channel Change in Large Rivers

Channel Change in Large Rivers

Research published in Earth Surface Processes and Landforms (2011, 36: p.1563–1576. doi: 10.1002/esp.2165) looks into the effects tributaries have on main-channel width.

Using publicly available SPOT-5 imagery from Google Earth, tributary junction geometries and downstream changes in channel width below these junction were catalogued along a ~2200 km reach of the Mekong River. The Mekong flows over sections of varied geology and as such provides a valuable site to study the varying influences of such constraints. The use of publicly available imagery, such as that provided by Google Earth, provides a unique platform for large scale assessments of channel planform and adjustments to be made. This research represents one of the first such studies, which previously have been hindered by the time consuming and expensive nature of obtaining relevant data.

Of the 284 junctions identified, the majority (66.2%) were acute. However 12 (4.8%) were found to be normal (90°) and 75 (30%) were found to be obtuse. This latter number is in contrast to previous studies over similar spatial scales which found little evidence of obtuse junctions. Meander extension of the incoming tributary and deflection of the tributary across bedrock shoulders were found to be the dominant geomorphological causes of obtuse tributary junctions. The relationship between the width of the tributary channels and the width of the mainstem upstream and downstream of the confluences was analysed. It was observed that, over the whole reach, a slight narrowing occurred immediately below tributary junctions. Although the changes themselves were small, the slight net narrowing is shown to be statistically significant. The observed relationship is shown to vary considerably with geology.

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