Flood Country: An Environmental History of the Murray-Darling Basin

By Emily O'Gorman

Floods in the Murray-Darling Basin are crucial sources of water for people, animals and plants in this often dry region of inland eastern Australia. Even so, floods have often been experienced as natural disasters, which have led to major engineering schemes. Flood Country explores the contested and complex history of this region, examining the different ways in which floods have been understood and managed and some of the long-term consequences for people, rivers and ecologies.

The book examines many tensions, ranging from early exchanges between Aboriginal people and settlers about the dangers of floods, through to long running disputes between graziers and irrigators over damming floodwater, and conflicts between residents and colonial governments over whose responsibility it was to protect townships from floods.

Flood Country brings the Murray-Darling Basin's flood history into conversation with contemporary national debates about climate change and competing access to water for livelihoods, industries and ecosystems. It provides an important new historical perspective on this significant region of Australia, exploring how people, rivers and floods have re-made each other.

• Language: English
• Publisher: CSIRO PUBLISHING
• Release date: Aug 1, 2012
• ISBN: 9780643106666

Book preview

Flood

Country

AN ENVIRONMENTAL HISTORY OF THE MURRAY-DARLING BASIN

Emily O’Gorman

University of Wollongong

© Emily O’Gorman 2012

All rights reserved. Except under the conditions described in the Australian Copyright Act 1968 and subsequent amendments, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, duplicating or otherwise, without the prior permission of the copyright owner. Contact CSIRO PUBLISHING for all permission requests.

National Library of Australia Cataloguing-in-Publication entry

O’Gorman, Emily.

Flood country: an environmental history of the Murray-Darling basin/by Emily O’Gorman.

9780643101586 (pbk.)

9780643106659 (epdf)

9780643106666 (epub)

Includes bibliographical references and index.

Floodplain management – Darling River (Qld. and N.S.W.)

Floodplain management – Murray River (N.S.W.–S. Aust.)

Wetland management – Darling River Watershed (Qld. and N.S.W.)

Wetland management – Murray River Watershed (N.S.W.–S. Aust.)

Darling River Watershed (Qld. and N.S.W.) – Environmental

aspects.

Darling River Watershed (Qld. and N.S.W.) – History.

Murray River Watershed (N.S.W.-S. Aust.) – Environmental

aspects.

Murray River Watershed (N.S.W.–S. Aust.) – History.

333.73160994

Published by

CSIRO PUBLISHING

150 Oxford Street (PO Box 1139)

Collingwood VIC 3066

Australia

Front cover and title page:

WC Piguenit

The flood in the Darling 1890, 1895

oil on canvas 122.5 x 199.3 cm

Art Gallery of New South Wales

Purchased 1895

Set in 8/12 Adobe Lucida and Adobe Minion Pro

Edited by Elaine Cochrane

Cover and text design by Andrew Weatherill

Typeset by Desktop Concepts Pty Ltd, Melbourne

Index by Russell Brooks

Printed in China by 1010 Printing International Ltd

CSIRO PUBLISHING publishes and distributes scientific, technical and health science books, magazines and journals from Australia to a worldwide audience and conducts these activities autonomously from the research activities of the Commonwealth Scientific and Industrial Research Organisation (CSIRO). The views expressed in this publication are those of the author(s) and do not necessarily represent those of, and should not be attributed to, the publisher or CSIRO.

Original print edition:

The paper this book is printed on is in accordance

with the rules of the Forest Stewardship Council®.

The FSC® promotes environmentally responsible,

socially beneficial and economically viable

management of the world’s forests.

Contents

Acknowledgements

Conversions

Abbreviations and terminology

Preface

Introduction

CHAPTER 1 Gundagai 1852: the town that moved

CHAPTER 2 Experimentation and regulation: pastoralism and mining, 1850 to 1890

CHAPTER 3 Bourke 1890: the birth of engineering

Colour plates

CHAPTER 4 Federation, engineering, and a ‘watershed’ perspective, 1890 to 1956

CHAPTER 5 Mildura and the Murray River 1956: the failure of engineering

CHAPTER 6 Challenging national development: dams and irrigation, 1956 to 1990

CHAPTER 7 Cunnamulla 1990: the town that did not flood

Conclusion

Bibliography

Index

Acknowledgements

Many people have helped to bring this book to publication. I would like to thank all those from CSIRO Publishing who have been involved in its production. Flood Country is based on my doctoral research, which I undertook in the School of History at The Australian National University. It was an inspiring place to be a postgraduate student, and the insights offered by staff, students, and visitors of the School have carried through to this book. I am lucky to have had Tom Griffiths as a PhD supervisor and mentor. Through example and advice, he has encouraged an attentiveness to sources, environments and places, and to the different voices of history within them. Our conversations about ways of telling stories in environmental history have been important influences on this book. The advice of Libby Robin, Nicholas Brown and Joe Powell was also central to how this research developed, and I am deeply grateful to them.

The final stages of researching and writing this book were completed at the Australian Centre for Cultural Environmental Research (AUSCCER) at the University of Wollongong during a postdoctoral candidacy funded through the Australian Research Council (FL0992397). My colleagues there have given me important time and support during this period. I would particularly like to thank Lesley Head who encouraged me to continue this project at the Centre.

Other people who have helped this book along, through comments on various presentations of research and chapter drafts as well as through conversations, are: Brit Andresen, James Beattie, Denis Byrne, Jane Carruthers, Kirsty Douglas, Brian Finlayson, Don Garden, Leah Gibbs, Geoff Ginn, Heather Goodall, Tim Hasted, Barry Higman, John Jansen, David Jenkins, Darrell Lewis, Cameron Muir, Eric Pawson, Stephen Pyne, Tiffany Shellam, Frances Steel, Gerry van Dooren, Thom van Dooren, Clare Wallace, the members of the Ecological Humanities Group, and members of the Science and Justice Group at the University of California Santa Cruz. Many people gave generously of their time during research trips to study particular places and in subsequent conversations. I would especially like to thank Harry Edwards and the late Allan Tannock and Ted Lawton.

During the course of researching and writing this book two American university departments hosted me for short but important periods: the School of Life Sciences at Arizona State University and the History of Consciousness Program at the University of California Santa Cruz. This work was published with the assistance of grants from the Australian Academy of the Humanities and The Australian National University.

Supported by

Conversions

This book uses the measurements quoted in primary sources, except where conversions to contemporary (metric) units have been necessary for comparison or clarity.

Imperial to metric

1 acre = 0.405 hectares

1 inch = 25.4 millimetres

1 foot = 30.5 centimetres

1 yard = 0.914 metres

1 mile = 1.61 kilometres

1 pound = 0.45 kilograms

1 acre foot = 0.123 hectare metres

(Acre feet and hectare metres are units of volume, i.e. acre = area, feet = depth)

1 imperial gallon = 4.55 litres

1 US gallon = 3.79 litres

1 short ton = 0.907 metric tonnes

Other measurements

1 cusec = 28.35 litres per second

1 megalitre = 1 000 000 litres

Abbreviations and terminology

Preface

In 2008 the Macquarie River made headlines around Australia. Newspapers reported that floodwater was being ‘stolen’. A group of scientists had claimed that irrigators had built unapproved earth embankments along the river. The embankments, the scientists maintained, would illegally divert flood flows to drought-stricken farms. The scientists argued that ‘harvesting’ floodwater in this unmonitored way could damage the internationally recognised Macquarie Marshes wetlands downriver. The ecology of the wetlands depends on sizeable flood flows. Floodwaters in turn attract thousands of birds, which breed during flood events. Graziers also rely on floods to rejuvenate pastures and replenish water supplies in the lower Macquarie. Journalists reported that irrigators were stealing environmental flows intended for the marshes, and had done so for years without prosecution. A spokesman for the irrigators in the area claimed that they were being victimised by governments, graziers, and environmentalists.¹ These newspaper reports about this region, located on the eastern edge of the Darling river system in NSW, came in the wake of national discussions about environmental degradation along the iconic Murray River as Australians reassessed, and sought to reshape, their relationships with rivers.

A year later, in another part of the Darling river system, floods again made headlines, but for a different reason. The town of Bourke, located on the upper reaches of the Darling River in NSW, flooded, causing $6 million of damage to property and infrastructure in the town. The state government declared Bourke a ‘natural disaster zone’ and the Federal government initiated financial assistance to those who suffered losses from the flood.²

More recently, floods in parts of the Murray and Darling river systems in 2010 and early 2011, including along the Murrumbidgee River in NSW and the Loddon River in Victoria, caused damage to property, infrastructure, and crops. They simultaneously broke an intense drought in the southern regions of Australia. These floods also fed into the politics surrounding the release of the Guide to the Proposed Basin Plan by the Murray-Darling Basin Authority. This preliminary document, and the Plan itself, were intended to reform water use throughout the Murray and Darling river systems. Historically, changed flows and less water in rivers, and on floodplains – as a result of agricultural, domestic, and stock watering uses – has led to significant environmental degradation. This degradation had been compounded by the drought. Following these floods, some people argued that many of the most pressing water use problems, particularly the over-allocation of river water for irrigation, were no longer critical and that the urgent action proposed by the Guide was no longer necessary.³

These instances, of conflict on the Macquarie, disaster in Bourke, and both conflict and disaster in 2010 and 2011, draw attention to the complex ways in which floods in the Murray and Darling river systems are entangled in the lives and livelihoods of residents of flood country and ultimately impact upon the nation. Floods in these river systems are central to the boom-and-bust character of the watercourses, and the environments and ecologies with which they are connected. ‘Boom-and-bust’ environments, as Libby Robin and Leo Joseph have recently noted, are also cultural concepts.⁴ Boom times, within a region frequently in drought (busts), have shaped understandings of floods as simultaneously important sources of water and ‘natural disasters’. This often fraught duality has created frequent conflict in a region that has become Australia’s agricultural heartland.

I undertook much of the research on which this book is based during the ten-year drought in the Murray and parts of the Darling river systems which ended in most regions in 2010. When I told people about my research, a common reply was, ‘it’s a good thing you’re working on a history’. To many people, floods in these rivers seemed to be a thing of the past. It is not unusual for people to think that the biggest floods, and droughts, are behind them and will not happen again, as this history will show.

I wrote this book out of a curiosity about floods and a passion for history. In the context of the recent drought, I also thought that this history of floods could provide an alternative perspective on the Murray and Darling river systems. I hoped that paying attention to floods would yield a different narrative about the region, one that could perhaps provide new insights into people’s relationships with the rivers and the inland more generally; to show that histories of rivers, floods, and floodplains are important and contested and that they are connected to the present and future. I still hold those hopes. Now, the context has changed. There have been a number of large floods in the Murray and Darling river systems, as well as along coastal Queensland. People feel a more immediate resonance with past floods. Yet, we tend to look primarily to floods that have occurred within living memory for understanding, reflection, and planning. For example, many discussions during and immediately after the Brisbane River floods in January 2011 referred almost exclusively to the floods that occurred along the river in January 1974, although there have been many others. In this new context, this book has an additional purpose: to give more historical depth to such discussions.⁵ This book is about floods in the Murray and Darling river systems, but I hope that those who live with other rivers will gain an appreciation that all Australian rivers flood, and each has a unique flood history and future.

Endnotes

1  Lewis and Wilkinson (2008a); Clarke (2008); ‘Flood plain development stealing water’, The West Australian, 25 February 2008; Lewis and Wilkinson, (2008b).

2  ‘Rudd offers Federal help to Bourke flood victims’, ABC Rural, 19 February 2009.

3  ‘Vic road repair bill hundreds of millions’, SMH, 1 February 2011; ‘Farms wiped out as floods move through Victoria’, ABC News, 23 January 2011; ‘Residents evacuated as Queanbeyan floods’, ABC News, 9 December 2010; ‘Murrumbidgee flood danger period eases’, ABC News, 13 December 2010; ‘Call for Federal flood help for the Riverina’, 13 December 2011; ‘Floods Deepen Murray-Darling Basin Feud’, The Australian, 6 January 2011; ‘Murray Murmurings: what’s happening to the plan?’, Crikey, 31 January 2011; ‘PM wants Murray plan progress despite floods’, ABC News, 6 January 2011.

4  Robin and Joseph (2009).

5  See also Evans (2011).

Introduction

Together the Murray and Darling river systems define what is now known as the Murray-Darling Basin. The web of rivers and their catchments that comprise the Basin cover parts of four states (Queensland, NSW, Victoria and South Australia) and the entire Australian Capital Territory. The Great Dividing Range forms the eastern edge of the Basin, and it is here that most of the rivers have their headwaters. The Basin is a significant part of the total area of Australia, comprising one-seventh or 14 per cent of the continent.¹ Within this vast area are diverse local environments, from the mountainous regions of the Great Dividing Range to the flat blacksoil floodplains of the Darling River, the red gum forests of the Murray, and the chains of ponds in the far west of the Basin. There is a wide diversity of environments even within these regions. They are connected through the rivers and floods, which drain into the Southern Ocean through a common mouth (if the water reaches it) near Goolwa in South Australia.

There are no large cities within the Basin, except for Australia’s capital, Canberra. Today it is an area dominated by agricultural industries. In the census years 2005–06, 84 per cent of the land in the Basin was owned by agricultural businesses, and 67 per cent of the land was used for growing crops and as pasture. Agricultural production also used the greatest amount of water in the Basin river systems, accounting for 83 per cent of all water consumed in that period.² The region produces a significant portion of Australia’s agricultural goods (comprising 39 per cent of Australia’s total agricultural value in 2005–06), especially food. Most rice grown in Australia is cultivated in the Basin, and it produces large percentages of the national totals of oranges, apples, wheat and pork.

Many crops that are farmed in the Basin are grown through irrigation, predominantly cotton, fruit, rice and nuts. Many dairy farmers also irrigate pastures.³ Most of the watercourses that comprise the Basin have been regulated for agriculture through large dams, off-river farm storages, and other built works, significantly changing river flows. One hundred and five large dams (more than 10 metres in crest height) stood in the Basin in the year 2000, just under a quarter of all large dams in Australia.⁴

The Murray-Darling Basin and the role of these industries have been the focus of national debates over the last few decades, and increasingly in recent years. These debates provoke confronting and difficult questions: how do we live in a land dominated by drought and flood? how should water and changing environments be managed? Floods are important in these debates; and so is history. These questions are not new. The histories of these questions need to be considered in order to shape water futures. People’s changing relationships with rivers and floods in the Murray and Darling river systems have shaped the environment, the way the rivers flow, and the political landscape in which these questions need to be asked.

Figure 0.1: Map of the Murray-Darling Basin in 2011, showing case study areas. (Map by Ian Faulkner. www.ianfaulknerillustrator.com.)

Floods have also shaped diverse understandings of the environment, and people’s lives and livelihoods. As major sources of water in dry regions, floods have been highly valued, sources of heated debate, and the rationale behind engineering schemes; they have also been seen as ‘natural disasters’, causing death and destruction. The idea of ‘natural disasters’ is clearly also deeply cultural, as scholars have established.⁵ Our understandings of events as disasters are directly influenced by where and how we live and how we understand our places, especially how much damage is caused to built works and agriculture and how many human lives are lost.

The label ‘natural disaster’ in some sense also classifies an event as unusual.⁶ But floods in Australia challenge such a classification. Floods are central to river hydrologies and ecologies in many Australian rivers. Although large floods are unpredictable in an absolute sense, they occur often enough, like bushfire or storm events, that they are frequently followed by a retrospective sense of fatalism. Continued damage from floods (they were on average the most costly ‘natural disaster’ in Australia between 1967 and 1999), shows that many Australians have not yet learnt to live with the rivers’ changing flows.⁷

Flood country

This book explores people’s changing relationships with, and understandings of, floods and the rivers and floodplains of the Murray and Darling river systems, from 1850 to early 2011. It takes its starting date from roughly the time when permanent colonial settlement began in the Australian inland.⁸ The earlier, more transient ventures of explorers and colonists into the region are included only where they reference particular floods.

Focusing on this time frame has allowed me to examine the period of immense cultural and environmental change since British colonisation. Aboriginal people have profoundly shaped diverse environments throughout the continent for approximately 55 000–60 000 years. British colonisation began a second major, much more concentrated, human environmental disruption, characterised by the ramifying ecological consequences of Western concepts of control over environments, ideas about a stable and unchanging nature, and faith in technology.⁹

I pay particular attention to how largely Anglo-Celtic newcomers struggled to gain knowledge about floods, including through their own experiences and through information shared by Aboriginal people. In addition, I explore how understandings and management frameworks developed around floods; how waves of migrants from a variety of different places shaped inland rivers and floods, particularly following the Second World War; the ways in which changing international contexts influenced national and regional approaches to environments; and finally, how local environments and the wider climate have altered in various ways over this 160-year period. These histories have been central in shaping current preoccupation with and politicisations of rivers, floods, and floodplains, in the Murray- Darling Basin and beyond.

The mainly Christian, Anglo-Celtic colonists came from environments very different from those of inland Australia. Rivers in Britain flooded, but those rivers and floodplains had vastly dissimilar hydrologies, ecologies and soil compositions, and were influenced by place-specific weather conditions. Many Australian rivers are characterised by their variability, in contrast to the more consistent and abundant flows of other rivers around the world, including those in Britain and continental Europe. Such variability was unexpected. An expectation that rainfall and river flow was relatively consistent led early colonists who passed through an area that had received good rainfall to assume that the area was generally well watered. For example, when surveyor and explorer John Oxley attempted to follow the course of the Macquarie River in 1818 he came across what we now know as the Macquarie Marshes in high flood. Based on the quantities of water he saw and unaware that water in the wetlands fluctuated substantially, he speculated that there may be an inland sea further west.¹⁰

Figure 0.2: An early flood in colonial New South Wales. This image possibly depicts a flood that occurred along the Murray and some of its tributaries in 1870. (‘A flood in New South Wales’, 1873. ISN00/02/73/SUPP, State Library of Victoria. Published as a supplement in The Illustrated Sydney News and New South Wales Agriculturalist and Grazier, February 1873.)

The unique flood hydrologies of the many rivers of the Murray and Darling river systems received substantial attention from early colonists and explorers as they attempted to understand these new environments. Many large floods were (and are) highly unpredictable, occurring without an annual or interannual pattern. Sometimes, bafflingly for settlers, a river began to flood very quickly without any rain or even any clouds in the sky. An early description of these types of floods on the Darling River comes from a newspaper report in 1848, which relayed knowledge of the sudden onset of floods by a member of one of Charles Sturt’s exploring parties:

the system of the Darling, which is a mere chain of ponds in a vast basin, of which the desert is a part … is subject to instantaneous inundations, described to the writer by a gentleman of Captain Sturt’s party as ‘giving brief notice by a loud continuous distant roar, when the waters are seen advancing in one mighty sheet along the horizon, in a perpendicular wall or wave, of twenty feet in height, prostrating the largest trees, and sweeping every unprotected object before it, subsiding as rapidly as it advances’.¹¹

Sturt also described a flood on the Darling River that he witnessed in 1844, on his third and final expedition into the inland. This was possibly the same flood as the one in the account above, but recounted in more restrained terms:

Figure 0.3: A postcard of dry flooded country in South Australia. (‘Camel team in flooded country, South Aust’, 1913. nla.pic-an23217498. National Library of Australia.)

at a distance of more than 300 miles from its sources, that river [Darling] rose from a state of complete exhaustion, until in four days it overflowed its banks. It was converted in a single night, from an almost dry channel, into a foaming and impetuous stream, rolling along its irresistible and turbid waters, to add to those of the Murray.¹²

Yet, when his party returned to the same place the following year it was completely dry. Sturt used this story in his Narrative of an Expedition into Central Australia to illustrate a general point that inland Australia’s rainfall, and hence its river flow, was irregular. However, he made an ‘exception’ of the Murray, because it experienced annual seasonal rises in flow from snowmelt and rainfall:

Uninfluenced by the sudden floods to which the other rivers of which we have been speaking are subject, its rise and fall are equally gradual. Instead of stopping short in its course as they do, its never-failing fountains have given it strength to cleave a channel through the desert interior.¹³

Sturt was famous for his conviction, based on Oxley’s speculations, that he would find an inland sea in Australia. His three expeditions into the inland were partly or entirely dedicated to this purpose. The Murray was the closest he came to finding an inland sea, and he revelled in its comparatively steady flows. The Murray was, however, capable of both very large floods and completely drying up, albeit less commonly than the Darling.

Years of little rainfall also challenged many early colonists. The word ‘drought’ in Australia gathered new meaning. Droughts in Australia often lasted years, not days as in many European countries. As late as 1896, Australian-born meteorologist HC Russell explained how ‘drought’ was used in Australia, differentiating it from its use in England, in a paper he presented to the Royal Society of New South Wales:

And it may be explained that the word drought is not used here in the sense that it is often used in England and elsewhere, that is, to signify a period of a few days or weeks, in which not a drop of rain falls, but it is used to signify a period of months or years during which little rain falls, and the country gets burnt up, grass and water disappear, crops become worthless and sheep and cattle die.¹⁴

It was, at least partly, the possibility of having both long droughts and large floods that made Australia’s environments, especially the inland, so different. Russell wrote:

There are parts of the world in which you never hear of drought, but they tell you they have years of floods, and years of moderate rains, but nothing that can be called a drought, and yet we have in these variations of rainfall exactly the same causes at work, which make in another place a serious drought; that is, a variation in the annual rainfall, and in the temperature and winds … The interior of Australia and many other places are of this character.¹⁵

Droughts and floods together helped to create particular hydrologies.¹⁶ As demonstrated by the quotes from Russell, ‘drought’ and ‘flood’ are invested with particular meanings that are influenced by local environmental circumstances. Historian Don Garden has noted that the meaning of ‘drought’ also encompasses cultural and economic dimensions.¹⁷ The same is true of ‘flood’, and I explore these shifting meanings in this book.

The variability in rivers’ flows have led many people throughout this period to see floods as a ‘waste’ of water. For instance, historian Tim Bonyhady has persuasively argued that WC Piguenit’s painting The Flood in the Darling, 1890 was intended by the artist to be an argument for water conservation; that is, damming floodwater for use during droughts for irrigation and water supply more generally. The image depicted a wide expanse of still floodwater, with billowing clouds above. This argument for storing floodwater was gaining political momentum at the time the painting was completed in 1895. In contrast to this message of changing the environment, the painting also attempts to convey the beauty of this flooded landscape in the style of the European Romantics. An additional layer of meaning is that the 1890 flood along the Darling River was widely seen as a national calamity because it caused stock losses that numbered in the millions and threatened to destroy the important wool-loading town of Bourke in NSW (discussed further in Chapter 3).¹⁸

The complex cultural meanings that have been given to floods are also evident in the phrases ‘flood country’ and ‘flooded country’. These terms were first used by settlers in the 1850s. Initially a simple description of flooded land, these evocative words came to describe the way the landscape had been shaped because it had been flooded. Even in the harshest of droughts, the words conjured up the image of the imagined water covering the land. For graziers, these words were shorthand for land that not only was good for sheep and cattle grazing as it was fertile floodplain, but was also where floods might endanger livestock. The words have especially (but not exclusively) been used by graziers as well as early surveyors, and have endured in some grazing regions. The terms have been used to describe floods and floodplains around Australia but are especially associated with the Murray and Darling rivers and their tributaries, a historically important sheep-grazing area (Plate 1). As far as I can tell, they are uniquely Australian phrases.¹⁹

The word ‘country’ echoes Aboriginal concepts of land and water as well as relationships with particular regions.²⁰ Its use by graziers in these contexts may reflect the strong involvement of Aboriginal people in the pastoral industries, multifaceted colonial frontier relationships and environmental understandings, and connections with places as well as English notions of ‘country’ and ‘countryside’. In this way, the terms ‘flood country’ and ‘flooded country’ draw attention to the complexity and ongoing ramifications of colonisation and to processes of gaining knowledge of rivers and land. These terms also indicate a certain set of relationships with floods: to put it simply, floods are good because they regenerate vegetation, bring richness to alluvial soils and are sources of water, but they can also be dangerous.

I explore floods in terms of two dominant roles they have played in the Murray and Darling river systems since 1850: as ‘natural disasters’, and as part of the wider hydrology of rivers. In this context floods have been understood as both events and part of longer environmental rhythms. They have been managed as emergencies, but also within broader environmental and water policies, and have been understood as part of the way rivers flow.

Ancestral rivers: a deeper history of floods

Floods and rivers in the deep past were central to the formation of the Murray-Darling Basin as we know it today. Most of the area of the Basin was probably, at some point in the last 80 million years, a riverbed or floodplain. Australia and Antarctica, the final two pieces of the supercontinent Gondwana, began to separate slowly about 80 million years ago, and Australia moved north and Antarctica moved south. During this separation, part of the eastern edge of the continent uplifted, creating what we now know as the Great Dividing Range. At the same time the western plains sank, forming a large sloping basin with the new mountain ranges. The plains continued to sink and the mountains to rise. Vast rivers washed coarse sediment loads of clay, gravel and sand down from the mountains, filling in the basin until it was almost flat. Much of this region has been moulded by the coarse sediment carried by these rivers, and parts of the floor of the Murray-Darling Basin are now buried under more than 150 metres of these ancient deposits.²¹

To the west of the mountain ranges the Basin is generally flat, with a very slight south-west gradient, gradually getting flatter towards the river system’s mouth. This makes river water and floods in the Basin generally slow-flowing. As the climate fluctuated over millions of years, so did the rivers, and the various beds and floodplains of these shifting rivers now crisscross inland eastern Australia. Geomorphologists call such traces of older rivers ‘palaeochannels’.²²

For the last 4 million years the climate of southern Australia has fluctuated, but has generally become drier. As the climate began to dry, the forests that had stretched as far inland as present-day Balranald in NSW gradually retreated. At the same time the oceans that had stretched inland across the flat plain also retreated. An uplift near Swan Reach about 2.5 million years ago dammed the westward-flowing rivers into a giant lake, ‘Lake Bungunnia’, which began to empty when the dam was breached around 700 000 years ago.²³

Roughly 2.5 million years ago the planet entered its current pattern of long ice ages interspersed with much shorter interglacial warm periods (one of which we are now in). When the climate intermittently warmed, many of the ice caps and glaciers that covered large parts of the continents of Europe and America melted, forming huge fast-flowing rivers that carved vast gorges and canyons. Australia, however, had few ice caps and glaciers during the last glacial period. The climate fluctuated instead between short wet interglacials and long dry periods, but across these fluctuations generally continued to dry. The rivers flowing inland from the western mountain ranges gradually shrank and their flows became seasonal, drying in summer and flooding over extensive floodplains in winter.²⁴

When humans first arrived in Australia about 55 000–60 000 years ago, the rivers of the Basin followed similar courses but were much larger. About 25 000 years ago the Cadell Fault, running roughly north-south between Echuca and Deniliquin near the upper to middle reaches of the Murray, rose, forcing the Murray into a new course that dips south to avoid the barrier. During the Last Glacial Maximum, around 20 000 years ago, the river flows were at their lowest and some, like the Lachlan, stopped flowing completely. About 10 000 years ago the rivers became approximately their present size. These rivers still flow though the floodplains of their ancestors.²⁵

Some of the ancient rivers from millions of years ago moved underground, forming aquifers. These aquifers interacted – as some continue to interact – with surface rivers and floodplains. Their depth from the surface varies from place to place. Today, many different aquifers underlie the Murray-Darling Basin; these include the Great Artesian Basin, which covers large sections of the northern Darling river system, and the Murray Basin, which underlies parts of the western Murray river system and southern Darling river system.

Aquifers can overlap and some interact to a degree, feeding and taking small amounts of water to and from one another, but mostly they appear to behave independently. They are replenished by rivers and floods. Replenishment occurs mostly at the edges of the aquifers and headwaters of the rivers, where earth and rock are more porous. Some aquifers can also come very close to the floor of riverbeds and seem to interact regularly with stream flow, so they both are recharged by river water and give water back to rivers. An aquifer can also rise and fall, depending on a variety of surface and underground hydrological factors. Floods appear to raise some aquifers, and the recharge rate of some aquifers appears to increase during floods. Knowledge of aquifers in Australia is incomplete and the recharge rate of each is far from certain. A number of aquifers are pumped as a source of water supply for stock and crops. There is currently no effort to ‘balance’ extraction from aquifers with the rate at which they are replenished, an impossible task given the paucity of knowledge about them. However, in many areas of Australia there is a general understanding (based on local conditions and various indicators) that extraction of artesian water has been greater than the recharge rate.²⁶

Weather and hydrology: La Niña and more

Ancient geographical features of the Murray-Darling Basin interact with weather and climate systems, and together these significantly shape river and flood flows. The Great Dividing Range provides a point at which many rain-bearing weather systems break, feeding floods. Rain occurs throughout the Basin, with annual local averages of more than 1000 millimetres a year in the east generally decreasing to less than 300 millimetres a year in the west. Localised floods can occur beyond the mountain ranges.

A number of significant weather systems contribute to floods in the Murray and Darling river systems: low-latitude easterlies; oceanic cloud bands that move north and north-west across the continent; east coast and independently moving upper-level (‘cut-off’) lows that are particularly associated with rainfall over the headwaters of the eastern rivers; trade winds in the north-east; westerlies and cold front lows in the southern regions; and tropical systems that move inland in the most northern parts of the Basin.²⁷

The tropical systems are highly significant for the hydrology of the Darling river system. The rain from monsoon systems can be substantial, causing large floods in the north-western tributaries, such as along the Paroo, Warrego, and Balonne rivers. During floods, these rivers often join with each other across vast, flat floodplains. The tropical systems, as well as other weather systems that bring large rainfalls to the northern tributaries, mean that the Darling can experience floods without any local rain, as floodwaters move south from its northern tributaries. The Darling also has wide, flat floodplains along its mid and lower reaches so that floods can stretch for kilometres.

In the Murray river system, snowmelt in the southern ranges contributes to seasonal inflows in the winter and spring months and, sometimes, to large floods when these are accompanied by substantial rain. The lowland rivers, like the Murray, Murrumbidgee and Ovens rivers, meander and shift across the floodplains, working sediment both towards the sea and across the plains. The changing courses of the rivers are evident in a series of ‘palaeoscrolls’, which are abandoned curved reaches, and ‘oxbows’, where whole stretches of river have been cut off from a changed course. Oxbows create ‘billabongs’ when they are filled with water.²⁸

The rivers in the Darling system tend to flood during summer months and those in the Murray system in winter and spring, but rivers in both systems have been known to flood at various times of the year. In both river systems, floods are mostly slow-moving and sometimes can be anticipated weeks in advance. Flash floods, while less common, also occur, particularly in places where floodwater is confined or held up until suddenly released.²⁹

The weather and climatic influences on floods are significantly driven by the El Niño– Southern Oscillation or ENSO. ENSO is an interannual phenomenon that is, broadly, the result of interactions between changing ocean temperatures and surface pressures across the Pacific Ocean. Two points that are central to ENSO are the eastern Pacific Ocean off the coast of South America and the western Pacific in the region around Indonesia. These two areas are connected by weather systems and ocean currents, the barometric pressures and temperatures of which interact to cause generally dry conditions in one region and wet in the other.

Many of the underlying principles of ENSO have been understood by scientists since the early twentieth century. However, ENSO only became widely discussed in scientific circles after extensive research into ocean temperatures and the atmosphere following the Second World War, and more so after several severe ENSO events in the 1970s and 1980s.

In Australia, El Niño periods are associated with droughts in the eastern and central parts of the continent that can last for several years. They are now accepted by scientists as being the most common climatic condition in these regions. The opposite conditions, called La Niña, are less frequent, less severe, and last for shorter time spans. They bring increased rain to central and eastern Australia, including significant flooding, as in 2010–11. These general characteristics of ENSO are variable between events and local areas, and floods can sometimes occur during El Niño years. A similar phenomenon possibly operates across the Indian Ocean, influencing dry and wet periods in western and eastern Australia. The existence of an Indian Ocean Dipole, as it is called, is, however, contested.³⁰

Many rivers of the Murray and Darling systems have highly variable flows, and the flow of the Darling River is among the most variable of the world’s large rivers. Large floods that