This dataset contains data from a river multibeam and seismic survey which took place in 2013 and 2014 at scour sites within the Brahmaputra river basin in Bangladesh. The survey was carried out as part of a joint project between the Universities of Birmingham, Southampton and Exeter. "The sedimentology of fluvial megascours" was a scientific research project funded by NERC. The purpose was to collect the data necessary to validate the first generic numerical model of scour zone stratigraphy that will be widely applicable to a broad range of large rivers. River bed bathymetry data were collected using a multibeam echosounder. Sub bottom seismic profiling data were collected using a surface tow boomer and chirp system. Technical details of the survey are contained in the cruise report of the survey which comprises part of the metadata. Some of the data has been accepted for a publication in the journal 'Sedimentology' which will be published in 2018 with the title 'The Sedimentology of channel confluences'.