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Sedimentary Crisis at the Global Scale 2: Deltas, A Major Environmental Crisis

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Sedimentary Crisis at the Global Scale 2: Deltas, A Major Environmental Crisis

Jean-Paul Bravard

ISBN: 978-1-119-59761-2 March 2019 Wiley-ISTE 230 Pages

Description

The great deltas of the globe have been threatened for several decades but their decline now appears to be inevitable; they are receding and losing the fertility that supports their tens of millions of inhabitants. Our deltas are victims of the dramatic deterioration in the volume of continental sediment brought by rivers to the oceans.

By nature, deltas are fragile eco- and geological organisms. For centuries, they have been subject to human actions in the Mediterranean and European world, and today a deep crisis is affecting the great tropical deltas. A chapter is also devoted to concerns facing the Mississippi, an “aging delta of the new world”.

Sedimentary Crisis at the Global Scale 2 discusses possible strategies to protect the deltas of the world – or at least adapt them and their dependencies to the changes they face. Several models are possible, including comprehensive protection (such as in the Netherlands) and cautious and respectful opening to the forces of the oceans in an environment-first perspective.

Introduction ix

Chapter 1 Deltas: Young, Fragile and Threatened Environments 1

1.1 Long-term construction of deltas: general mechanisms 2

1.1.1 Processes and basic forms 2

1.1.2 Dynamics of construction and redistribution in progress 2

1.1.3 Young and unstable areas 5

1.2 Some of the Earth’s last great natural deltas: two deltas in the Arctic 8

1.2.1 The Lena Delta 8

1.2.2 The Mackenzie Delta 9

1.3 The Earth’s deltas: what is their current situation in the face of terrestrial and marine constraints? 11

1.3.1 The rise in sea levels 11

1.3.2 Sedimentary exhaustion of continents 13

1.3.3 Extraction of resources and accelerated subsidence of deltas 15

1.4 Subsiding deltas in Southeast Asia 16

1.4.1 An example of a young, mainly rural delta, the Huang-He 16

1.4.2 Urbanized deltas in Southeast Asia 16

1.5 Conclusion 25

Chapter 2 Old Societies and Deltaic Crises 27

2.1 Some vulnerable deltas in the Holocene during the long and medium terms 27

2.1.1 The Nile Delta, a condensed version of the history of the African climate 28

2.1.2 The lower Huang-He and its delta: a Holocene metamorphosis under anthropological control 29

2.1.3 The Rhône Delta during the Holocene: fluvial branches and the coastline record the history of its climate and society 35

2.2 The Rhine and the Meuse Deltas: from complete control of fluvial and marine waters to attempts at restoration to a natural state 36

2.2.1 The fight against fluvial floods 36

2.2.2 Hydraulic works and environmental objectives in the dyked zone 39

2.2.3 What kind of compatibility or synergy takes place between fluvial restoration and protection against flooding? 41

2.2.4 Defense of the Netherlands against the sea 42

2.3 Contemporary imbalances in the Old World 47

2.3.1 A delta with a reprieve: the Nile Delta 47

2.3.2 The Rhône Delta: changes in the basin and the delta 52

2.3.3 The Ebro Delta: alone against the sea 54

2.3.4 The delta of the Po plain: historical dispersion of weak points 57

2.3.5 The Danube Delta: still room for hope 59

2.4 Conclusion 61

Chapter 3 Tropical Deltas in Crisis, Between Open and Closed Formations 63

3.1 A delta that is both open and alive: the Ganges and Brahmaputra Delta 63

3.1.1 Rivers and a delta 64

3.1.2 The Ganges–Brahmaputra–Meghna plain, the most populated and the poorest on Earth 65

3.2 The Mekong Delta in a suspended status 78

3.2.1 A technical machine, constantly more complex 78

3.2.2 Extremely worrying emerging factors 87

3.2.3 What will be the management choices in the future? Giving preference to the scale of the basin 95

3.3 The Niger Delta: unlimited exploitation of black gold 97

3.3.1 The deltaic zone 97

3.3.2 The effects of the extraction of hydrocarbons on the environment 98

3.3.3 Serious social and political stakes at play 101

3.4 The Indus Delta, dramatically dried out 103

3.4.1 The delta and its coast 103

3.4.2 The deleterious effects of dams on water and sediment fluxes 103

3.4.3 A serious environmental, economic and social crisis 104

3.5 The Ayeyarwady, initial symptoms of imbalance? 106

3.5.1 Burma, a country on the cusp of development 106

3.5.2 The Ayeyarwady, an enormous conveyor belt 107

3.5.3 The delta: crisis or stability? 107

3.6 Conclusion 109

Chapter 4 The Aging Delta of a Country in the New World, the Mississippi 111

4.1 New Orleans: an “inevitable city on an impossible site” 111

4.1.1 “Discovering” the river 111

4.1.2 At the origins of New Orleans 112

4.1.3 An area with serious issues at stake 113

4.2 Floods and protection of the lower Mississippi valley and the delta since 1717 116

4.2.1 Initial protections 116

4.2.2 The beginning of generalized protections 117

4.2.3 The 1927 flood in the Mississippi valley 118

4.2.4 The Jadwin plan (1928) 119

4.2.5 Current protection elements 120

4.3 The “deltas” in the lower Mississippi valley, from wilderness to the current crisis 120

4.4 The Mississippi Delta stricto sensu: a natural zone in crisis 124

4.4.1 Flow and landscape dynamics 124

4.4.2 The Atchafalaya and its deltaic lobes 127

4.4.3 The conversion of delta marshes into free water and coastal regression 129

4.5 Hurricanes and their effects on the Mississippi Delta 132

4.5.1 Hurricane Katrina 132

4.5.2 What does the future hold for New Orleans? 134

4.6 Sediments in the Mississippi and equilibrium of the delta 137

4.6.1 Simply a reduction in inputs or a sediment deficit? 137

4.6.2 The rise in sea levels and climate change 138

4.6.3 Reconstruction of the marshes 138

4.6.4 Sedimentary management of deltaic branches and the future of the marshes 139

4.6.5 Coastal protection plan 140

4.7 Conclusion 141

Chapter 5 What Strategies Can Help Overcome the Delta Crisis? 143

5.1 Delta dynamics: contrasting budgets on a global scale 143

5.1.1 The progress of analytical approaches adds complexity to the understanding of deltas on a global scale 143

5.1.2 The unforeseen effects of scientific choices 145

5.1.3 Open, vulnerable systems 147

5.2 Some control logic for rivers and deltas 148

5.2.1 Situations involving crises and knowledge 148

5.2.2 Contemporary hydraulic engineering pitted against the dynamics of economic domination 149

5.2.3 Scientific knowledge at the service of policies on rivers and on their deltas: the case of the Mekong 151

5.2.4 Avatars and tribulations of geopolitics 153

5.2.5 Expert appraisal and conquest of engineering markets on deltaic land 154

5.3 What sustainability is there for deltas in the 21st Century? Comparative approaches 158

5.3.1 The typology of deltas as a function of the changes expected in the risk profile 158

5.3.2 Typology of deltas as a function of their energy consumption 159

5.3.3 The degree of vulnerability or the relative vulnerability of deltas to current changes 160

5.3.4 The notion of the tipping point of a delta and of the socioeconomic system 161

5.4 Actions at the scale of the continental fluvial system to rebalance the deltaic systems 162

5.4.1 Implementation of actions of sedimentary management 162

5.4.2 Establishment of current and future sediment budgets 165

5.5 The actions developed in the deltaic system in response to crisis situations 166

5.5.1 Structural solutions: dykes and fluvial levees 166

5.5.2 Some solutions for correction of the sedimentary deficit of deltaic plains 169

5.5.3 The sustainable solutions 171

Conclusion 177

Glossary 179

References 185

Index of Place Names 205

Index of Common Words 211