Barscale morphodynamics through the tidal-fluvial transition

Keevil, Claire Elizabeth

April 2016

Thesis or dissertation

© 2016 Claire Elizabeth Keevil. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

A complex transitional zone within river-estuary systems exists between fully-fluvial and fully-tidal conditions. This zone varies both spatially and temporally across a range of scales. The resultant sedimentary transport and depositional characteristics are, at present, poorly understood and a robust model that links processes to products across this complex zone is presently lacking.

Process-product relationships were investigated in two distinctive tidal-fluvial systems: the high fluvial flux mesotidal Columbia River estuary (USA), and the smaller fluvial flux macrotidal River Severn (UK). Spatially and temporally distributed three-dimensional flow and bed morphology data within the two transitions were coupled to sub-surface geophysical and core information.

High resolution bathymetric measurements collected within the Columbia River estuary transition zone allowed investigation of the variations in bedform and bar morphology. The dominant fluvial flow steers asymmetrical bedforms around local barforms, decreasing in size with increasing tidal influence. Barforms commonly have an apparently tidally-influenced lobate planform, however, investigations around a single bar indicated a fluvial origin, with tidal modification restricted to smaller-scale bedforms. Deposition within the River Severn appears fluvial, but the presence of a large tidal bore and strong flood tide is shown to hinder larger scale meander bend migration processes, also resulting in characteristic soft sediment deformation within bar deposits. The deformation may be important for palaeogeographical system reconstruction as tidal bores only form under limited conditions.

Investigations within these two very different systems reveal that both are fluvially-dominated, but with some tidal influence. Although the barforms and surrounding bedforms appear to be fluvial they contain important, although subtle, evidence of the tidal nature of the system. This may be spatially limited and could be hard to detect in both cores and/or geophysical measurements. Careful analysis of the smaller-scale features of ancient lowland fluvial systems is required to observe evidence of this subtle tidal influence.

[Thesis includes co-authored articles from Journal of hydraulic research, 2015, v.53, issue 3:
and Earth surface processes and landforms, 2015, v.40 , issue 12: ]

Department of Geography, Environment and Earth Sciences, The University of Hull
Parsons, Daniel R.
Sponsor (Organisation)
Natural Environment Research Council (Great Britain); British Sedimentological Research Group
Qualification level
Qualification name
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