Engineers Australia

The Evolution of East Coast Australian Estuaries and Implications for Geotechnical Investigation

Daniel Bishop

The heavily developed and populated east coast of Australia comprises numerous estuary systems, evolved within deeply incised valleys east of the Great Dividing Range. Sediment sequences that fill these estuaries are complex and pose many challenges to engineering development. Not least of these challenges is predicting the distribution and behaviour of the thick deposits of soft estuarine clays that fill these valleys.

Unfortunately there appears to be a significant gap between current understanding of coastal evolution in geoscience research fields and simplified concepts typically utilised by the local geotechnical profession. A significant part of the problem has been the absence of any active research to translate and apply up-to-date geological concepts into the realm of geotechnical investigation.

A conceptual framework will be presented that integrates recent developments in coastal estuary models with the concepts of sequence stratigraphy and morphodynamics. Influences of past sea level change and climate change will be discussed. Application of the framework to geotechnical investigations in estuaries will be described with reference to recent work conducted in the Richmond River. Some key geotechnical outcomes arising from this work will be highlighted.

The ideas presented in this lecture have been developed during research into the distribution and behaviour of soft clays in the Richmond River Estuary conducted at the University of Newcastle and in cooperation with the NSW RTA.

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