In the half-light of morning sunrise on the banks of the Dhaleshwari River, Bangladesh, a woman dressed in a bright blue sari carefully leads her young daughter into the water. She hopes the waters will provide them with a place to wash and cleanse themselves afresh for the coming day. Yet to reach the water’s edge, she has had to clamber down the eroding riverbank made unstable by local riverbed sand mining and climb through a wide swath of domestic and plastic waste. She now dips her hands into water covered by a thin white froth, which has come from an open sewer 30 metres upstream. As she begins her morning ritual, she glances around to see her neighbours washing themselves and their children, and the clothes of their families, in the surrounding filthy water. The waters of one of the world’s great river systems should not be like this.
The Dhaleshwari and the world’s other large rivers have nurtured and sustained the growth of human civilisation, and today they are home to huge populations and human infrastructure. These large river basins also possess a freshwater ecology that is both vital to global biosustainability as well as supporting human populations through fisheries and agriculture. However, as pressures on these great river basins grow – from burgeoning populations, energy, resource and infrastructure demands, increased agricultural, industrial and domestic water usage, as well as increased accessibility to many remote regions – so the anthropogenic stresses on these vital waterways are increasing rapidly.
A recent synthesis of research on the world’s 32 greatest rivers reveals the perilous state of many large river basins. Hydrological change induced by a warming climate, which is highlighted daily in the news media, will lead to shifting patterns - in both space and time - of floods and droughts. Such hydrological changes are affecting rivers across all latitudes and altering how we forecast the probability of recurrence of certain size floods based on historical data. In addition, the growth of large-scale damming in the past 20 years, especially in China and a range of developing countries, has fuelled huge river basin change and fostered both economic growth and severe environmental damage. Not only are such megadams influencing flow, sediment yields and ecology, but they may have widespread economic, political and societal ramifications – such as the shifting balance of power in the Nile River basin due to Ethiopia’s construction of its Grand Renaissance Dam, currently slated for completion in 2022.
In addition to the relatively well-publicised stresses associated with climate change and large-scale damming, the world’s big rivers are also facing serious threats from other human activities. Pollution is now so bad in some big rivers, such as the Ganges, that the waters are a toxic mixture of faecal, industrial, agricultural, plastic and domestic waste, which causes widespread disease and thousands of deaths every year. Such dire pollution helped prompt legal moves in India in 2017 to protect the river by declaring it had the same legal rights as humans, a decision subsequently overturned by the Indian Supreme Court. Researchers at the University of York in the UK have recently reported on the widespread extent of antibiotic pollution in some of the world’s rivers, in places up to 300 times safe levels.
Several countries also have plans for extensive transfer of water between river basins and/or withdrawal of water to help address regional hydrological and water use imbalances. Both India and China have designs for river interlinking schemes that are essentially remaking the physical geography of their major river basins. With such interlinking comes the prospect for the spread of non-native species, as has been witnessed in large river basins in Europe and America.
Sediment mining and dredging are also now producing a crisis in the availability of sand, and causing deleterious effects on riverine ecology, river bank stability and the downstream accumulation of sediment in the world’s great river deltas, which support vital agricultural production and huge populations. The effects of sediment starvation caused by sediment mining and trapping behind dams add to the substantial problems already faced by such deltas, and their inhabitants, due to land subsidence, sea-level rise and the pollution of groundwater. As a catastrophic example, the World Health Organization has called the staggering scale of arsenic contamination in the groundwaters of the Ganges delta ‘the largest mass poisoning of a population in history’.
All these stressors, either singly or in combination and in often non-linear ways, thus serve to fragment many of the world’s great rivers, dividing them up into compartments that have greatly altered flows and sediment exchange, and making a viable ecosystem often impossible.
Despite all of these ills, solutions may be still be available to help ameliorate some of these effects, but only through an inclusive governance framework that demands interactions and collaborations between all stakeholders – river dwellers, scientists and planners, industry, energy sector, governments and NGO’s – and action in the very near future. We need a range of actions that will force us to budge in our appreciation, and social/political awareness, of these troubled waters.
Astonishingly, we still lack the reliable data needed to characterise the flow of water and sediment within most of the world’s big rivers: yet, without this, how are we to assess, and cope with, the effects of large-scale change, or set standards by which sustainable practices can be implemented? The good news is that the last twenty years have seen massive improvements in our ability to measure our great rivers, both on the ground and remotely from space, and feed these data into increasingly sophisticated and realistic numerical models that can aid assessment of the impacts of change. Our appreciation of the flux of virtual water, and the role of green (rainfall water in plants) and blue (fresh surface and ground water) water budgets, has also improved dramatically, allowing more complete analysis and planning of how water is transferred around the world and that must inform how river basins are managed. The political will to incorporate this knowledge is, however, often lacking.
We also need more holistic analyses of energy generated from hydropower dams, calling for both fuller consideration of alternatives (from in-stream turbines through to alternative energies), more efficient use and less waste of energy/water, as well as more sophisticated hydropower water management strategies that could ameliorate some of the damaging effects on downstream riverine channel and floodplain ecology. Such plans are common sense but require working social and political structures in order that any management can be sustainable, highlighting the huge difficulties still faced in governance of nearly all the worlds big river basins. This will only change when these issues rise to the surface of geographical concern and public awareness.
In 1977, the visionary geomorphologist Luna Leopold asked that we adopt a ‘modicum of reverence for rivers’ and highlighted that economic considerations must not be the only metric by which to judge the health of rivers. Around the world, Leopold’s call has gone largely unheeded. Politically and socially, we must ask: if we can develop essential new knowledge and scientific discoveries by sending probes to the depths of the oceans or the surface of Mars, is it too radical to expect that we possess a reliable understanding of the world’s great rivers on which so much of the world’s human population, and a huge slice of the Earth’s natural biodiversity, rely? The drip of the water clock is becoming a torrent, and we simply cannot wait any longer in many large river basins before irreparable changes ensue, with potentially catastrophic effects on human livelihood and ecosystem integrity. Now is the time for reverence to give way to shouting.
• Jim Best holds the Jack and Richard Threet Chair in Sedimentary Geology at the University of Illinois at Urbana-Champaign, USA, where he is also professor of Geography & GIS, and holds affiliate positions in the Department of Mechanical Science and Engineering and Ven Te Chow Hydrosystems Laboratory. His recent Nature Geoscience review Anthropogenic Stresses on the World’s Big Rivers can be found here.
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