Macquarie University
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Channel bifurcation and adjustment in multi-channelled floodplain wetlands

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posted on 2022-07-13, 01:26 authored by Neda Yousefi

 Multi-channelled rivers and floodplain wetlands are geomorphologically dynamic systems that provide vital resources and habitat. River bifurcation is a critical element of channel formation and adjustment in these systems. Bifurcations may be stable or unstable, leading to anastomosing reaches and also wholesale avulsions that create new channels. The division of discharge, stream power and sediment load between channel branches may be uneven and change over time. Depending on the spatial patterns of branches and the associated processes of channel adjustment, either continuous or discontinuous channels will occur that define the structure of floodplain wetlands into the future. New evidence from the Macquarie Marshes, a large, low energy, floodplain wetland system in semi-arid Australia, demonstrates the importance of bifurcations and return points leading to maintenance of channel capacity despite loss of flow to the floodplain. Estimates of bankfull discharge and unit stream power suggest that channels are able to effectively transmit water and sediment to downstream reaches until a threshold is crossed whereby channels become increasingly inefficient and decline in size rapidly downstream. This ultimately leads to channel breakdown where channels cannot be maintained and where water floods out onto alluvial surfaces at channel termini. The historical trajectory of channel behaviour in hyper-avulsive reaches of this system showed fluctuations in channel capacity adjustment from 1992 to 2018, including large variations in bankfull width, depth and cross-sectional area, as well as bankfull discharge and unit stream power. Erosion is central to the formation of bifurcations and avulsion processes in the Macquarie Marshes. Analysis of erosion risk showed that despite channel ranking according to likelihood and consequence of channel change, few sites experienced significant changes between 2012 and 2018. Overall, understanding the biophysical character and behaviour of multi-channelled floodplain wetlands is important for water resources and environmental management.


Table of Contents

Chapter 1: Thesis introduction -- Chapter 2: Methodological literature review -- Chapter 3: Research sites and methods -- Chapter 4: Assessment of recent channel change using DEMs -- Chapter 5: Spatial pattern of channel bifurcation and return nodes in the Macquarie Marshes -- Chapter 6: Recent historical channel adjustment in the Southern Macquarie Marshes -- Chapter 7: Rapid assessment of key hazards and risks associated with channels in the Southern Macquarie Marshes -- Chapter 8: Discussion -- Chapter 9: Conclusion – References -- Appendix 1: Geomorphology Site Assessment form -- Appendix 2: Plots of relation between geometric and hydraulic parameters


"This thesis submitted for the degree of Doctor of Philosophy, October 2019."

Awarding Institution

Macquarie University

Degree Type

Thesis PhD


Thesis (PhD), Faculty of Science and Engineering, Macquarie University

Department, Centre or School

Department of Earth and Environmental Sciences

Year of Award


Principal Supervisor

Tim Ralph

Additional Supervisor 1

Paul Hesse

Additional Supervisor 2

Michael Chang

Rights Copyright Neda Yousefi 2020




vii, 173 pages