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7 - Synchronous estuaries: sediment trapping and sorting – stable morphology

Published online by Cambridge University Press:  01 September 2009

David Prandle
David Prandle
Affiliation:
University of Liverpool
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Summary

Introduction

Suspended sediments in estuaries generally increase upstream to produce a ‘turbidity maximum’ (TM) in the vicinity of the upstream limit of saline intrusion, with concentrations hugely increased relative to open-sea conditions. Uncles et al. (2002) summarise observational studies of these TM and discuss mechanisms responsible for their formation. Here, for the case of strongly tidal estuaries, we develop generic quantitative expressions to represent the mechanisms producing these high sediment concentrations. The aim is to identify the scaling parameters which determine the sensitivities to sediment type (sand to clay), spring to neap tides and drought to flood river flows. Recognising the long-term stability of estuarine bathymetry, despite the continuous large ebb and flood sediment fluxes, an additional aim is to identify feedback processes that maintain this stability.

Postma (1967) first described the mechanisms responsible for estuarine trapping of fine sediments, namely gravitational circulation, non-linearities in the tidal dynamics and delays between resuspension and settlement. However, these respective roles are difficult to isolate either from observations or from models. Hence, it has been difficult to gain a clear insight into the scaling of these processes and to estimate their sensitivities to changes in either marine or fluvial forcing or to internal parameters.

Earlier studies

Postma (1967) described the nature of sediment distributions in tidal estuaries and indicated likely controlling mechanisms.

Type
Chapter
Information
Estuaries
Dynamics, Mixing, Sedimentation and Morphology
 , pp. 175 - 204
Publisher: Cambridge University Press
Print publication year: 2009

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