NJG93-1-02
2013
Channel-bed changes in distributaries of the lake Øyeren delta, southern Norway, revealed by interferometric sidescan sonar
93
1
pp. 25–35
978-82-92-39481-6

Multiple high-resolution bathymetric data from interferometric multibeam surveys over a three-year period were used to investigate channel-bed morphology and changes in distributary channels of the Øyeren delta plain, the largest freshwater delta in northern Europe. Most of the erosion over the three-year period occurred at the outside of channel bends and upstream ends of islands, while deposition mostly occurred at the inner bends. Overall, there appears to be a net aggradation within the channels over the three-year period. The dominant bedforms registered are dunes.

The dune morphology is complex with large variations in wavelength, height, lee-side angles, scour depth and crest-line curvature. Their size shows a correlation with flow depth. Another prominent feature registered is that of scours occurring at different settings and at different scales. The largest scour recorded was 23 m deep (below water level) in 2004, and 19.5 m in October 2007. It has migrated more than 20 m downstream and up to 7.5 m of sediments have been removed vertically over the three-year period. Over the same period, 10 m of vertical deposition has taken place at the upstream end of the scour. Between June and October 2007, relatively little erosion has taken place at this locality, apart from a bank collapse at the scour margin. The smaller and more localised scours occur at the lee sides of some dunes, commonly extending well into the stoss side of the downstream dune and with occasional prominent spurs on the flanks.

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