Sub-bend scale flow–sediment interaction of meander bends — A combined approach of field observations, close-range remote sensing and computational modelling

• We study three meander bends in a natural river in high resolution.
• We combine field survey, close-range remote sensing and computational modelling.
• The effect of flood on the point bar depends on the stage of the bend development.
• Parts of the point bar that are long inundated are likely to gain net deposition.
• The transport magnitude and morphological change are not fully interconnected.

Various field-based studies of meander development have been realised, yet fluviomorphological processes and their spatial patterns over bends are not fully understood. In this paper, the processes of three natural meander bends during a flood event are dissected using a unique study approach, which combines traditional field surveying, close-range remote sensing, and computational modelling. The combined study approach improves the spatial and temporal resolutions of the data compared to traditional survey methods, although the bathymetric data collection needs improvement. The analyses indicate that the influence of a flood on the morphological changes of point bars depends on the stage of the bend's development. The point bars may also experience lateral growth during low discharge. However, the point bar is too large a unit to find simplified relationships between the discharge and morphological changes. Instead, one should concentrate on different parts of the bend and the point bar. In general, the longer the inundation period of one part, the more probable that the area will experience net deposition. The magnitude of the sediment transport and the net morphological change are not interconnected: Areas of net erosion and deposition can experience either high or low sediment transport rates during a flood. The results are compared with earlier theories of meander development, which are also assessed.