Megawater: Replumbing the Modern World
For centuries humanity has built dams to tame waterways for our consumption, but our obsession with engineering is becoming unsustainable.
by Mark Everard
Manipulation of water flows to and from land is as old as settled agriculture. Irrigation and river management practices are found widely across the ancient human world, constituting one of the most fundamental technologies to enhance natural soil productivity and overcome limitations to survival and progress. Indeed, they were pivotal in the ascent of humanity from the moment Homo sapiens appeared in the fossil record in Africa about 130,000 years ago to eventually displace wider groups of hominids.
Settled agriculture in turn marked a revolution in human ingenuity, bringing into cultivation and domestication various species of plants and animals to provide staple foods. It signaled an evolution in human consciousness to the extent that farmers’ decisions were premised upon future yields, rather than merely current availability, providing the need for the establishment of permanent communities, new levels of social structure and communication, and for the transfer of knowledge between individuals and generations.
These innovations laid some of the foundations of modern culture. Writing systems were developed, empires were created often in the quest for more resources, and monumental buildings were constructed by a betternourished populace less vulnerable to the vagaries of hunting and gathering. Many assign the origin of economic systems to the transition to settled agriculture as, released from the daily drudgery of pursuing food, societies were able to internally differentiate responsibilities and labour, and so to need a trading system for fair exchange between social groups.
The evolution of agricultural principles and applications, critically including the management of water, was followed by advances in the entrainment of water for defensive, industrial, municipal and other purposes. These broad and fascinating innovations have substantially shaped human history.
A brief history of dams
Dams were an early innovation in the rise of human civilizations. ICOLD, the International Commission on Large Dams, defines a dam as a barrier or structure across a stream, river or waterway to confine and then control the flow of water. Dams vary in size from small slip dams built to intercept springs and small streams emerging from hillsides and gorges, generally for farm use, through to progressively larger engineered structures, generally used for water supply, hydro power and irrigation and including some of the modern world’s most massive civil engineering schemes.
Across the globe, major river systems have been progressively dammed over a period of centuries. The earliest unambiguous records of human agriculture appear in the ‘fertile crescent’ of Mesopotamia, between the rivers Tigris and Euphrates in land now covered by modernday Iraq, with evidence of river engineering found in the ruins of irrigation canals over eight thousand years ago.
At 104 meters (340 feet) long, 61 meters (200 feet) high at the crest and built of masonry blocks with a gravel and stone centre, Sadd elKafara, the Dam of the Pagans, is the world’s oldest big dam built between 2950 and 2750 BC and today crumbling in the Egyptian desert.2 The remains of water storage dams dating back to at least 3000 BC have also been found in Jordan, Egypt and other parts of the Middle East, though no more large permanent dams were built in Egypt until the twentieth century. In China, a system of dams and canals was constructed in 2280 BC, the Dujiang irrigation project once supplying 800,000 hectares in China.
The 1,500-year old Grand Canal, one of the wonders of ancient China, was once the largest artificial river of the preindustrial world and was also the first to have lock gates. It was used to transport rice from the wet south of the country, primarily from the monsoonfed Yangtze valley, to centers of population in the north. One of the oldest dams still in use today is an earth and rock fill embankment dam built around 1300 BC in what is now Syria.
The building of the Marib Dam in Yemen began around 750 BC and took 100 years to complete, comprising an earth embankment 4 meters high with stone sluices to regulate discharges for irrigation and domestic use. In 1986, the existing Marib Dam was raised to a height of 38 meters, creating a reservoir of 398 million cubic meters of water. The famed though potentially mythical ‘hanging gardens of Babylon’, considered one of the Seven Wonders of the Ancient World and attributed to the neoBabylonian king Nebuchadnezzar II, who ruled between 605 and 562 BC, were probably more miraculous for their water engineering than for the vegetation they supported.
In Sri Lanka, ancient chronicles and stone inscriptions state that numerous dams and reservoirs were built as early as the third century BC. Interbasin canals built for irrigation augmented many of these large reservoirs. One of these large dams, the Minneriya dam, was constructed during the reign of King Mahasen (ad 276–303), and was still intact when it was rediscovered in 1900. It was restored in 1901 and is still in use today. More than fifty other ancient dams in Sri Lanka have been restored.
The Romans built an elaborate system of low dams for water supply. The most famous was the Cornalbo earth dam in southern Spain, which had a height of 24 meters (78 feet) and a length of 185 meters (606 feet). After the Roman era, very little development in dam construction took place until the end of the sixteenth century, when the Spanish began to build large dams for irrigation. European engineers refined their design and construction knowledge in the nineteenth century, giving rise to the capability to construct dams to a height of 45–60 meters (150–200 feet).
The first recorded dam in India was on the Cauvery river (‘Kaveri’ in the native tongue), the southernmost of the three great river catchments draining the Deccan peninsula. Here, the Grand Anicut (in Tamil, anai means ‘to hold’ and katta is ‘something that is built’) spanned the Cauvery near Tiruchirapalli in the time of King Karikala in the second century ad. The dam is still in use today, albeit massively altered and reinforced, and is just one of many ancient dams subsequently reconstructed throughout India, with a particularly pronounced period of dambuilding as long ago as the thirteenth century ad, when the Hoysala Empire ruled much of modernday Karnataka in the Deccan peninsula.
The Sayamaike dam, one of the oldest dams in Japan, was built early in the seventh century ad and, after several modifications and a raising of height, it is still in use today. Several ancient dams from the thirteenth to the sixteenth century in Iran are also still in use today.
In the 1950s, the GermanAmerican historian Karl A. Wittfogel coined the term ‘hydraulic civilizations’ to describe societies managing their use of water through technology rather than local access.3 Today, much of the developed world constitutes hydraulic civilization, with many emerging nations aspiring to exploitation of technology rather than local access to natural resources to meet their water needs. Living with a significant legacy of engineeringdependent water management, we risk losing sight of other meanings of water, ranging from its cultural and spiritual importance to different people through to a respect for the ecosystems we depend on to maintain the quality and quantity of the basic resource of water that enters our ever more complex societal plumbing systems.
‘Megawater’
Early human civilizations had largely built their cities in proximity to natural sources of water. This situation remained mostly unaltered until the first half of the twentieth century. Early instances of large dams, such as Hoover and Aswan High, served the primary purpose of controlling flows rather than redirecting water over long distances.
Major change is seen today in many large dam schemes in China, including the Three Gorges Dam, where numbers of large dams form part of a massive infrastructure to redirect water northwards across not only drainage basins but almost the entire country. This was viewed as a political necessity, as demands from farming and industry in the north of the country had drained the Yellow River dry, converting part of its bed into little more than unproductive desert during dry seasons. China’s capital city, Beijing, had relied on aquifers recharged from the Yellow River, yet these too had receded by 61 meters (200 feet) over the last four decades of the twentieth century, with 90 percent of underground water depleted around the city as part of a cycle of aridification, also leading to some land subsidence.
Saline intrusion into depleted aquifers compounds threats to water supply in the North China Plain. Yet the north of China constitutes its breadbasket and industrial heartland, comprising twothirds of the nation’s croplands, even though it receives only one fifth of national rainfall. The political view of the solution was to tap into the monsoonfed rivers to the south of the country, diverting them northwards to change the nation’s hydrology on an epic scale.
In April 2003, water started flowing into Beijing along a canal 61 meters (200 feet) wide and as long as France. This water had begun its journey in a tributary of the Yangtze river (the world’s fourthlargest river system) nearly a thousand kilometers (600 miles) to the south, diverted into the translocation system by the massive Danjiangkou Reservoir, which is being raised to 168 meters (550 feet), displacing an estimated quarter of a million people. China proudly claims that this water translocation scheme is the largest engineering project under taken anywhere on the planet, echoing the pride of early Western dam pioneers in humanity’s dominance over nature. It was planned for completion in time for the 2008 Beijing Olympic Games.
Amazingly, it is just one of three huge diversion projects designed to replumb the nation, diverting water from the south into the arid north. The four diversions comprising the total southtonorth water transfer project are due for completion by 2050, and will reroute some 45 million cubic meters of water per year. The target recipients of this expensive water are the cities of the north, with little or no provision for the poor people that the channels will bypass, nor for the people of the lower Yangtze now deprived of ‘their’ water. Recognizing the ever tightening water crisis, China is also driving a range of watersaving measures on farmland which include water deficit irrigation, use of straw mulch to reduce evaporation, changing crop structure and water saving education for farmers, although this policy change is not, at least yet, implemented nationally.
Worryingly, the sheer scale of aspirations to replumb China is not without precedent elsewhere in the world. There is toplevel political support and momentum behind an ambitious River Interlinking Project to solve the perceived problem of regional imbalance of water access across India.12 Under this scheme, which has huge associated costs approximating 1 percent of India’s gross national product over twentyfive years and an implementation timescale to match, engineering solutions will enable the transfer of vast volumes of water be tween major drainage basins. While in theory it will help overcome the devastating effects of seasonal floods and ensure energy security, the main benefit is perceived to be a more even sharing of water across the country to stimulate food and commodity production as well as other economic activities. This project builds upon a project first mooted in 1972 to interlink the Ganga (Ganges) river, the huge glacialfed system to the north of the country, and the Cauvery river, which is monsoonfed and is the southernmost of the three drainage basins of the Deccan peninsula. The concept of the River Interlinking Project builds from this basis, joining up other great river systems such as the Godavari, Narmada and Krishna rivers into a form of ‘national grid’. The project is unprecedented in scale and ambition, joining rivers across climatic zones, and results are highly unpredictable in terms of ecological impacts on whole catchments, deltas and the coastal zones, the spread of disease and organisms, human consequences and overall efficacy.
Fred Pearce coined the term ‘megawater’ to describe the stages beyond merely controlling flows, including the engineering of large dams and associated infrastructure on a pharaonic scale.13 This mega scale engineering approach may demonstrate our ingenuity, boost economic prospects for targeted beneficiaries in the immediate term, and become emblematic of ‘man’s power over nature’. However, it also raises huge questions about sustainability and equity in terms of dependence upon engineering structures, substantial energy inputs and political stability, not to mention the consequences for regions from which water is drained in a climatechanging world. Irrigation may be essential to feed today’s substantial and tomorrow’s escalating human populations. However, if most irrigationbased civilizations have failed throughout human history,14 it is clearly essential that we call into question the sustainability of our future technological approach rather than assume that the lessons of history no longer apply.
The extent to which dams as well as other water diversion schemes modify river flows around the world is staggering. Israel has long been a pioneer of water diversion for its agricultural and urban needs, with similar schemes across Pakistan, Egypt, India and elsewhere in the world. This includes Libya, at least until the revolution of 2011 hardly the world’s most democratic or equitable regime, which is now ‘min ing’ the vast fossil groundwater reserves beneath the Sahara Desert to serve its burgeoning demands. Libya’s Great Manmade River, the world’s largest underground network of pipes and ducts, moves 6.5 million cubic meters per day from an ancient aquifer beneath the Sahara Desert, fueling the nation’s aspiration to export crops. And, as we have seen, the hydrology of South Africa has been massively reengineered to the advantage of those living in the arid interior of the country. Spain’s large dams regulate 40 percent of the country’s river flow. Current estimates suggest that some 30–40 percent of irrigated land worldwide now relies on dams, and that dams generate 19 percent of world electricity. However, there is today a declining pace of large dam construction as optimal sites are used up and societal opposition intensifies.
Dams and the future
The demand for water is spiraling across the world in response to booming population, industrialization and shifting lifestyles. There are also mounting concerns about how society is providing for these needs, in technical terms but also in addressing the needs of all people on an equitable basis. The ‘hydrological amplifier’ of climate change is likely only to compound concerns about adequate supply of water.
Dams offer some solutions. However, like all technological innovations, they bring with them both benefits and costs, many of which are poorly evaluated if considered at all. Yet, even in the light of what we know today, as many as 250 new dams are being built each year,15 and over half of the world’s major river systems are seriously affected by fragmentation and flow regulation resulting from the construction of dams.16 Yesterday’s innovations need to be reexamined in the ‘modern world’, including optimization of benefits for all and assessment of broader costs which it may or may not be possible to mitigate.
Also, in considering large dams, we have to be cognizant that there is no one type of ‘large dam’. There are different designs which interact differentially with ecosystems and people depending upon geography, climate, population density and the decisionmaking process. Further more, dams of different scales—from giant structures such as China’s Three Gorges Dam to small hillside ‘slip dams’ such as those common at farm scale across South Africa and Australia, and run-of-river small dam schemes through to tidal barrages—offer a different scale and scope of benefits, beneficiaries and negative implications.
It is timely to reappraise the contribution of dams to our quest for a world in which the needs of all are met equitably and sustainably.
Dr Mark Everard is a scientist, author and broadcaster.
This is an extract from ‘The Hydropolitics of Dams’, published by Zed Books.
