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AVIJIT GUPTA, PHD, is Honorary Principal Fellow at the School of Earth, Atmospheric and Life Sciences at University of Wollongong, Australia.
Preface xiii
1 Introduction 1
1.1 Large Rivers 1
1.2 A Book on Large Rivers 3
References 6
2 Geological Framework of Large Rivers 7
2.1 Introduction 7
2.2 The Geological Framework: Elevated Land and a Large Catchment 8
2.3 Smaller Tectonic Movements 9
2.4 The Subsurface Alluvial Fill of Large Rivers 10
2.5 Geological History of Large Rivers 12
2.6 Conclusion 14
Questions 14
References 14
3 Water and Sediment in Large Rivers 17
3.1 Introduction 17
3.2 Discharge of large Rivers 17
3.3 Global Pattern of Precipitation 18
3.4 Large River Discharge: Annual Pattern and Long-Term Variability 21
3.5 Sediment in Large Rivers 26
3.6 Conclusion 32
Questions 32
References 33
4 Morphology of Large Rivers 35
4.1 Introduction 35
4.2 Large Rivers from Source to Sink 35
4.3 The Amazon River 38
4.3.1 The Setting 39
4.3.2 Hydrology 39
4.3.3 Sediment Load 39
4.3.4 Morphology 42
4.4 The Ganga River 44
4.4.1 The Setting 44
4.4.2 Hydrology 46
4.4.3 Sediment Load 46
4.4.4 Morphology 47
4.5 Morphology of Large Rivers: Commonality and Variations 48
4.6 Conclusion 52
Questions 52
References 52
5 Large Rivers and their Floodplains: Structures, Functions, Evolutionary Traits and Management with Special Reference to the Brazilian Rivers 55Wolfgang J. Junk, Florian Wittmann, Jochen Schöngart, Maria Teresa F. Piedade and Catia Nunes da Cunha
5.1 Introduction 55
5.2 Origin and Age of Rivers and Floodplains 57
5.3 Scientific Concepts and their Implications for Rivers and Floodplains 59
5.4 Water Chemistry and Hydrology of Major Brazilian Rivers and their Floodplains 60
5.5 Ecological Characterisation of Floodplains and their Macrohabitats 62
5.6 Ecological Responses of Organisms to Flood-Pulsing Conditions 64
5.6.1 Trees 65
5.6.2 Herbaceous Plants 66
5.6.3 Invertebrates 66
5.6.4 Fish 67
5.6.5 Other Vertebrates 68
5.7 Biodiversity 68
5.7.1 Higher Vegetation 69
5.7.2 Animal Biodiversity 71
5.8 The Role of Rivers and their Floodplains for Speciation and Species Distribution of Trees 71
5.9 Biogeochemical Cycles in Floodplains 73
5.9.1 Biomass and Net Primary Production 73
5.9.1.1 Algae 73
5.9.1.2 Herbaceous Plants 74
5.9.1.3 Trees of the Flooded Forest 75
5.9.2 Decomposition 76
5.9.3 The Nitrogen Cycle 77
5.9.4 Nutrient Transfer Between the Terrestrial and Aquatic Phases 78
5.9.5 Food Webs 79
5.10 Management of Amazonian River Floodplains 80
5.10.1 Amazonian River Floodplains 80
5.10.2 Savanna Floodplains 82
5.11 Policies in Brazilian Wetlands 82
5.12 Discussion and Conclusion 84
Acknowledgements 89
References 89
6 Large River Deltas 103
6.1 Introduction 103
6.2 Large River Deltas: The Distribution 104
6.3 Formation of Deltas 104
6.4 Delta Morphology and Sediment 110
6.5 The Ganga-Brahmaputra Delta: An Example of a Major Deltaic Accumulation 112
6.5.1 The Background 112
6.5.2 Morphology of the Delta 113
6.5.3 Late Glacial and Holocene Evolution of the Delta 114
6.6 Conclusion 115
Questions 115
References 116
7 Geological History of Large River Systems 119
7.1 The Age of Large Rivers 119
7.2 Rivers in the Quaternary 121
7.2.1 The Time Period 121
7.2.2 The Nature of Geomorphic Changes 123
7.2.3 The Pleistocene and Large Rivers 124
7.2.3.1 The Glacial Stage 124
7.2.3.2 The Transition 125
7.2.3.3 The Interglacial Stage 127
7.3 Changes During the Holocene 127
7.4 Evolution and Development of the Mississippi River 128
7.5 The Ganga-Brahmaputra System 133
7.6 Evolution of the Current Amazon 137
7.7 Evolutionary Adjustment of Large Rivers 141
Questions 142
References 142
8 Anthropogenic Alterations of Large Rivers and Drainage Basins 147
8.1 Introduction 147
8.2 Early History of Anthropogenic Alterations 148
8.3 The Mississippi River: Modifications before Big Dams 149
8.4 The Arrival of Large Dams 151
8.5 Evaluating the Impact of Anthropogenic Changes 156
8.5.1 Land Use and Land Cover Changes 157
8.5.2 Channel Impoundments 159
8.6 Effect of Impoundments on Alluvial Rivers 161
8.7 Effect of Impoundments on Rivers in Rock 163
8.8 Large-scale Transfer of River Water 166
8.9 Conclusion 167
Questions 168
References 169
9 Management of Large Rivers 173
9.1 Introduction 173
9.2 Biophysical Management 177
9.3 Social and Political Management 178
9.3.1 Values and Objectives in River Management 179
9.3.2 International Basin Arrangements 180
9.4 The Importance of the Channel, Floodplain, and Drainage Basin 180
9.5 Integrated Water Resources Management 182
9.6 Techniques for Managing Large River Basins 183
9.7 Administering the Nile 184
9.8 Conclusion 188
Questions 189
References 190
10 The Mekong: A Case Study on Morphology and Management 193
10.1 Introduction 193
10.2 Physical Characteristics of the Mekong Basin 194
10.2.1 Geology and Landforms 194
10.2.2 Hydrology 196
10.2.3 Land Use 197
10.3 The Mekong: Source to Sea 199
10.3.1 The Upper Mekong in China 199
10.3.2 The Lower Mekong South of China 199
10.4 Erosion, Sediment Storage and Sediment Transfer in the Mekong 202
10.5 Management of the Mekong and its Basin 204
10.5.1 Impoundments on the Mekong 204
10.5.2 Anthropogenic Modification of Erosion and Sedimentation on Slopes 206
10.5.3 Degradation of the Aquatic Life 207
10.6 Conclusion 208
Questions 208
References 209
11 Large Arctic Rivers 211Olav Slaymaker
11.1 Introduction 211
11.1.1 The Five Largest Arctic River Basins 213
11.1.2 Climate Change in the Five Large Arctic Basins 213
11.1.3 River Basin Zones 214
11.2 Physiography and Quaternary Legacy 216
11.2.1 Physiographic Regions 216
11.2.1.1 Active Mountain Belts and Major Mountain Belts with Accreted Terranes (Zone 1) 216
11.2.1.2 Interior Plains, Lowlands, and Plateaux (Zone 2) 217
11.2.1.3 Arctic Lowlands (Zone 3) 218
11.2.2 Ice Sheets and Their Influence on Drainage Rearrangement 218
11.2.3 Intense Mass Movement on Glacially Over-steepened Slopes 218
11.3 Hydroclimate and Biomes 220
11.3.1 Climate Regions 220
11.3.2 Biomes 220
11.3.3 Wetlands 224
11.4 Permafrost 224
11.4.1 Permafrost Distribution 224
11.4.2 Permafrost and Surficial Materials 226
11.4.3 Contemporary Warming 226
11.5 Anthropogenic Effects 228
11.5.1 Development and Population 228
11.5.2 Agriculture and Extractive Industry 228
11.5.3 Urbanisation: The Case of Siberia 228
11.6 Discharge of Large Arctic Rivers 229
11.6.1 Problems in Discharge Measurement 229
11.6.2 Water Fluxes 229
11.6.3 Water Budget 231
11.6.4 Nival River Regime 232
11.6.5 Lakes and Glaciers 234
11.6.6 River Ice: Freeze and Break Up 236
11.6.7 Scale Effects 237
11.6.8 Effects of River Regulation 238
11.6.9 Historical Changes 238
11.7 Sediment Fluxes 239
11.7.1 Complications in Determining Sediment Fluxes Both Within Arctic Basins and to the Arctic Ocean 239
11.7.2 Flux of Suspended Sediment and Dissolved Solids 240
11.7.3 Historical Changes in Water and Sediment Discharge in the Siberian Rivers 240
11.7.4 Suspended Sediment Sources and Sinks in the Mackenzie Basin 242
11.7.4.1 Sediment Yield in the Mackenzie Basin 242
11.7.4.2 West Bank Tributary Sources 243
11.7.4.3 Bed and Bank Sources 245
11.8 Nutrients and Contaminants 249
11.8.1 Supply of Nutrients 249
11.8.2 Transport of Contaminants 250
11.9 Mackenzie, Yukon and Lena Deltas 253
11.9.1 Mackenzie Delta 253
11.9.2 Lena Delta 253
11.9.3 Yukon-Kuskokwim Delta 256
11.10 Significance of Large Arctic Rivers 256
Acknowledgment 258
Questions 259
References 259
12 Climate Change and Large Rivers 265
12.1 Introduction 265
12.2 Global Warming: Basic Concept 266
12.3 A Summary of Future Changes in Climate 270
12.4 Impact of Climate Change on Large Rivers 271
12.5 Climate Change and a Typical Large River of the Future 273
12.6 Conclusion 277
Questions 277
References 278
Index 281
We have an intuitive recognition of large rivers although a proper definition is elusive. Even though it is difficult to define a large river, we would probably select the same 15 or 20 rivers as the biggest in the world. Potter identified four characteristic properties of large rivers: they drain big basins; they are very long; they carry a large volume of water; and they transfer a considerable amount of sediment (Potter 1978). It is, however, difficult to attribute quantitative thresholds to these, and not all big rivers exhibit these four characteristics. We associate large rivers with high discharge and sediment transfer, but both water and sediment vary over time and space and their data are difficult to acquire. It is easier to identify large rivers by the size of their drainage basins and their lengths; both are easier to measure.
Based on the areal extent of their drainage basin, Potter (1978) examined 50 of the world's largest rivers, ranked by Inman and Nordstrom (1971), starting with the Amazon. All but one of these rivers are more than 103?km long, and the smallest drainage basin is about 105?km2. These 50 rivers collectively drain about 47% of the land mass, excluding Greenland and Antarctica. The Amazon alone drains about 5% of the continental area. These rivers also have modified the physiography of a large part of the world. Table 1.1 lists the top 24 large rivers (Figure 1.1), ranked according to their average annual water discharge. Their ranks would change if the rivers were listed according to any of the other three properties.
There are other lists. Hovius (1998) tabulated the morphometric, climatic, hydrologic, transport, and denudation data for 97 river basins, all of which measured above 2.5?×?104?km2. Meade (1996) ranked the top 25 rivers twice: first, according to their discharge; and second, according to their suspended sediment load. The two lists do not match well. For example, large rivers such as the Zambezi or Lena carry a large water discharge but a low sediment load. Impoundments too have drastically reduced the once high sediment load of many rivers such as the Mississippi-Missouri. Over approximately the last 100?years, many rivers have been modified by engineering structures such as dams and reservoirs. The Colorado or the Huanghe (Yellow River) at present may not flow to the sea round the year. Such changes have also reduced the amount of sediment that passes from the land to the coastal waters. Large rivers such as the Nile or Indus have been associated with human civilisation for thousands of years and show expected modifications.
Table 1.1 Selected characteristics of 24 large rivers.
These figures vary between sources, although perhaps given the dimensions, such variations are proportionally negligible. Discharge and sediment figures are from Meade (1996) and Gupta (2007) and references therein. Drainage areas are rounded off to 106?km to reduce discrepancies between various sources. The Nile is not listed, even though it is 6500?km long. It does not qualify for this table as its water and sediment discharges are relatively low.
The great lengths of these rivers allow them to flow across a range of environments. The Mekong, for example, flows on both rock and alluvium, looking different (Figure 1.2). The end part of the river needs to adjust to all such environmental variations plus the Quaternary changes in sea level.
Fluvial geomorphology generally is based on small and logistically manageable streams. A study of large rivers is necessary, although difficult, for multiple reasons. Large rivers form and modify subcontinental-scale landforms and geomorphological processes. A high number of them convey and discharge a large volume of water and sediment to the coastal seas. An understanding of modern large rivers helps us to explain past sedimentary deposits. Large rivers, such as the Amazon (Mertes and Dunne 2007), and their deposits may reveal basinal and regional tectonics, past and present climate, and sea-level fluctuations. Management of the water resources of a large river is often an essential step toward the supply of water and power to a large number of people. We need to study large rivers for many such reasons.
Figure 1.1 A sketch map showing the location of 24 large rivers in the world: 1, Amazon; 2, Congo; 3, Orinoco; 4, Ganga-Brahmaputra; 5, Changjiang; 6, Yenisei; 7, Mississippi; 8, Lena; 9, Mekong; 10, Parana-Uruguay; 11, St. Lawrence; 12, Irrawaddy; 13, Ob; 14, Amur; 15, Mackenzie; 16, Zhujiang; 17, Salween; 18, Columbia; 19, Indus; 20, Magdalena; 21, Zambezi; 22, Danube; 23, Yukon; 24, Niger.
A number of individual large rivers have been studied and such studies published discretely. A collection of advanced essays on the general characteristics of large rivers, their selected case studies, and their utilisation and management is also available (Gupta 2007). In comparison, this volume is primarily an integrated textbook on large rivers and introduces the reader to the morphology and management of these huge conduits on which both the general physiography of the basins and utilisation of the resources of the rivers depend.
The discussion on large rivers starts with an account of their geological framework (Chapter 2) that determines where they can be located and also what their physical characteristics would be. The geological framework of a large river is based primarily on large-scale tectonics commonly driven by plate movements. An uplifted zone and the adjoining subcontinental-scale water catchment area are necessary requirements for a big river. Smaller tectonic movements may further modify the basin and the channel and explain their detailed morphological characteristics.
Figure 1.2 The Mekong. (a) On rock, downstream of Chiang Saen, northern Thailand. (b) On alluvium near Savanakhet, Lao PDR, photographed from the air. Note the difference in form and behaviour between the two reaches. Large rivers commonly are a combination of a number of similar variations.
Source: A. Gupta.
The regional geology should create a drainage basin large enough to accumulate enough precipitation to support and maintain the big river. Chapter 3 discusses the nature of water and sediment in a large river. The discharge in a large river is determined by various climatic criteria depending on its location: annual rainfall, seasonality in rainfall, and high episodic rain from synoptic disturbances such as tropical cyclones. The supply of water to large rivers could be from almost all parts of the watershed but the sediment supply generally is associated selectively with high mountains. For example, the discharge of the Orinoco is collected from most...
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