A multi-method study of bedload provenance and transport pathways in an estuarine channel

Abstract

Bedload transport pathways and provenance in the upper reaches of the Tay Estuary, Scotland have been investigated using a combination of three methods, analysis of bedform geometry and asymmetry using echo-sounding and side-scan sonar, the ‘McLaren Model’ of deducing sediment transport from grain size distributions and magnetic susceptibility measurements. The 13.5 km long study reach has been shown to be a complex mixing zone in which bedform asymmetry varies both temporally and spatially. Both grain size transport trends and magnetic susceptibility data suggest that the area is dominated by marine derived bedload but, to the south of the main channel axis, the contribution from fluvial input increases. A simple mixing model based on optimised linear programming has shown the relative contribution made to estuary bed sediments from marine and fluvial sources. With increased distance upstream the role of fluvial sources becomes more pronounced peaking at 24%. Together the results clearly illustrate the dominance of marine-derived bedload in the study area.