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Floodplain wetland formation and avulsion in the semiarid Tshwane-Pienaars Catchment, South Africa

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posted on 28.03.2022, 13:01 authored by Zacchary Larkin
Controls on floodplain wetland formation and river avulsion (channel relocation on the floodplain) are diverse and can include external (e.g. geology, climate) or internal (e.g. sediment deposition, erosion) drivers. Using a range of techniques including mapping historical channel change, morphological analysis of downstream channel characteristics and optically simulated luminescence dating of recently deposited floodplain sediment, this thesis investigates floodplain wetland formation and avulsion in the Tshwane-Pienaars Catchment in northern South Africa. The broadest scale control on river character and wetland development is catchment lithology, which affects floodplain width and accommodation space for unconfined alluvial reaches and floodplain wetlands. Downstream declines in discharge account for the overall morphology and behaviour of the Tshwane and Pienaars Rivers and their wetlands. Downstream channel diminution due to declines in discharge leads to aggradation of levees and alluvial ridges, and lateral adjustment occurs by channel migration and avulsion on the lower reaches of both rivers. Avulsion of the Tshwane River occurs autogenically during meander belt development in response to reductions in sediment transport capacity. The Tshwane River has a high avulsion frequency ( ̃4.6 avulsions ka⁻¹) and a high vertical overbank sedimentation rate ( ̃11 mm a⁻¹), which provides a well constrained dataset to demonstrate that sedimentation rate and avulsion frequency are correlated.

History

Table of Contents

Chapter 1. Introduction -- Chapter 2. Controls on river character, behaviour and floodplain wetland formation in the semiarid Tshwane-Pienaars Catchment, South Africa -- Chapter 3. Mechanisms and timescales of avulsion in a rapidly adjusting South African dryland floodplain wetland : Tshwane River, North West Province -- Chapter 4. Conclusion.

Notes

Bibliography: pages 67-71 Empirical thesis. Spine title: Tshwane-Pienaars Catchment : floodplain wetland formation and avulsion.

Awarding Institution

Macquarie University

Degree Type

Thesis MRes

Degree

MRes, Macquarie University, Faculty of Science and Engineering, Department of Environmental Sciences

Department, Centre or School

Department of Environmental Sciences

Year of Award

2015

Principal Supervisor

Timothy John Ralph

Additional Supervisor 1

Stephen Tooth

Rights

Copyright Zacchary Larkin 2015. Copyright disclaimer: http://www.copyright.mq.edu.au

Language

English

Jurisdiction

South Africa

Extent

1 online resource (v, 73 pages) colour illustrations, maps (some colour)

Former Identifiers

mq:44900 http://hdl.handle.net/1959.14/1073073