Extreme flood-driven bank erosion and sediment transport on a mega-river: Direct process measurements using integrated Mobile Laser Scanning (MLS) and hydro-acoustic techniques.

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.This methods paper details the first attempt at monitoring bank erosion, flow and suspended sediment at a site during flooding on the Mekong River induced by the passage of tropical cyclones. We deployed integrated Mobile Laser Scanning (MLS) and Multibeam Echo Sounding (MBES), alongside acoustic Doppler current profiling (aDcp), to directly measure changes in river bank and bed at high (~0.05 m) spatial resolution, in conjunction with measurements of flow and suspended sediment dynamics. We outline the methodological steps used to collect and process this complex point cloud data, and detail the procedures used to process and calibrate the aDcp flow and sediment flux data. A comparison with This article is protected by copyright. All rights reserved. conventional remote sensing methods of estimating bank erosion, using aerial images and Landsat imagery, reveals that traditional techniques are error prone at the high temporal resolutions required to quantify the patterns and volumes of bank erosion induced by the passage of individual flood events. Our analysis reveals the importance of cyclone-driven flood events in causing high rates of erosion and suspended sediment transport, with a c. twofold increase in bank erosion volumes and a fourfold increase in suspended sediment volumes in the cyclone-affected wet season.This research was supported by awards NE/JO21970/1, NE/JO21571/1 and NE/JO21881/1 (to the Universities of Southampton, Exeter and Hull, respectively) from the UK Natural Environmental Research Council (NERC). We thank the Mekong River Commission and Department for Hydrology and Water Resources in Cambodia for logistical support. Award of a University of Southampton Diamond Jubilee International Research Fellowship to JLB helped facilitate completion of this paper