Plan of an irrigation survey problem by Chin Chiu-Shao, 1247. The total length of the parallel canal is given as 118 li or 59 km. The irrigated fields are marked with the character tien, the major river dyke is called an, and the minor dykes cheng. Source: Needham, Joseph, (1959). Science and Civilisation in China.
Chinese practices for regulating the water supply, known as water conservation ?? (shuili), are as old as China’s civilization. The three major objectives of water conservation are irrigation, flood control, and transportation. The commitment to intensive water management has shaped Chinese history.
Access to fresh water is essential to human life. Domesticated plants also require water to survive, ideally in precisely regulated amounts. But the location, quantity, and timing of the water supply are highly variable. China’s monsoon climate, its location amid the watersheds for much of the eastern Himalaya snowpack, and its ecological diversity guarantee a water supply that fluctuates dramatically from place to place and from season to season. Control of water is at the heart of farming and, indeed, civilization itself, and water engineering is one of the areas in which humans have struggled most vigorously to free themselves from constraints imposed by nature.
Turning Water to Advantage
Water conservation is known in Chinese as shuili, which literally means, “turning water to advantage.” The objective of water conservation is to reduce the risk of flood and drought. The wet-rice agriculture of south China requires fields to be drained and flooded at different times in the life cycle of the crop. Water conservation for rice requires methods for ensuring the availability of water when needed and for letting it in and out of the fields when necessary. Historically, both drought and flood were concerns of the Chinese. Archaeologists have excavated drainage canals at the late Neolithic village of Banpo, which flourished around 7,000 years ago in the vicinity of modern-day Xi’an. And queries about rainfall and flooding are a preoccupation of the oracle bones, China’s first written documents, produced from the thirteenth to the eleventh century BCE. From the emergence of their civilizations, people in China devoted substantial energy to regulating the flow of water in riverbeds and to moving water out of its natural courses and into new channels and pools that met their needs for farming, transportation, and settlement. These activities have profoundly shaped Chinese history.
Irrigation and Drainage
Irrigation is the name for the set of technologies devoted to bringing water to places where it is needed for growing crops, while drainage systems channel excess water out of fields. In China irrigation and drainage were practiced widely, beginning in the Neolithic era. By the time of the Song dynasty (960–1279), the world’s most intensive and highly engineered agricultural economy, irrigation and drainage allowed people to grow crops where it would otherwise have been impossible, particularly in the Yangzi (Chang) delta. Irrigated and drained agriculture supported the commercial revolution of the Song and the population growth of that and subsequent eras.
Irrigation systems include an intake, where water enters an engineered system from its natural course, and a series of branch canals that bring water directly to fields. Many systems also include gates that control the flow of water through the branch canals. Drainage systems rely on pipes or canals that move water downhill and frequently also involve piling up earth to create fields that are raised above the water table and isolated from the surrounding marshes by bunds (embankments) and polders.
The use of polders (low-elevation fields protected by earthen dikes) appears in Chinese texts dating to the Spring and Autumn period (770–476 BCE), a millennium before their emergence in Northern Europe. During the Song dynasty, the introduction of new strains of early ripening rice made double cropping possible, and there were many important improvements in fertilization and cultivation techniques. Water conservation was an essential element of the new intensive rice agriculture of the Song; in turn the promise of high yields rewarded the massive labor that water conservation demanded. During the Northern Song (960–1126), an expansionist state directly sponsored projects to drain wetlands, fill lakes, and irrigate dry lands. By the Southern Song (1127–1279), the government and large landowners collaborated on polder construction on a massive scale that transformed the Yangzi delta into the most populous and wealthy region of the empire and permitted intensive rice farming and commercial agriculture on the rich alluvial soil of former wetlands. The largest polders, which measured several square miles, were subdivided into smaller diked fields, demarcated by networks of natural streams and irrigation and drainage canals, and controlled by locks. Homes were situated on dikes and clustered around embankments. Boat traffic linked villages to the outside. Dikes also served as overland routes. Breaches in the earthen and stone walls would flood the villages as well as the fields. Hillsides were also leveled and diked to conserve soil, regulate water, and create terraces for wet-rice agriculture.
Water conservation initiatives often coordinated political, economic, and engineering challenges at a regional scale. Engineers had to regulate the speed, location, and timing of water flows throughout entire complex systems. It was often difficult to balance competing priorities, and individual water control projects were seldom effectively integrated. In the Yangzi delta, for instance, Song polders to the north of Lake Tai interfered with the lake’s drainage, which resulted in flooding along the Grand Canal. When the canal managers drained excess water, they inundated adjacent fields, to the wrath of landowners, who built embankments to block the water. Until the fossil fuel era, irrigation systems were created and maintained by human and animal labor. According to Song History, one instance of restoring thirty-six silt-clogged canals around the city of Suzhou in 1158 CE required 3.3 million man-days, an equal number of strings of cash, and more than 100,000 bushels of grain. Some 6,000–7,000 farmer-solders were resettled in Suzhou to maintain the system and prevent flooding. Water engineering on the Chinese scale required abundant labor.
Coastal land reclamation deserves special mention. The Pearl River delta around modern Guangzhou and Hong Kong is a human creation, engineered by coastal farmers who learned to capture alluvial silt to create fertile agricultural land. Seawalls, which create barriers between ocean water and fresh water, have been an important feature of Chinese water conservation. The seawall that began to extend south of the Yangzi to the southern side of Hangzhou Bay in the Tang allowed a region of China larger than the Netherlands to be transformed from a land of shallow inlets, salt marshes, sandbars, and brackish creeks into a world of drained polders and navigable canals that supported population densities that were among the world’s highest. Inside seawalls water becomes gradually less brackish, farmers can capture fertile sediments, and agriculture gradually overtakes salt production, fishing, and other coastal pursuits. However, like other massive waterworks, seawalls required constant attention to avert flooding and salinization. According to a 1347 description, rebuildi
ng approximately 6 kilometers of seawall (out of a total length of 400 kilometers) required 63,000 tree trunks and close to a million cubic feet of stone.
Along with canals and polders, irrigation and drainage systems included reservoirs, pools that stored water for future use. In central and south China, where rainfall was abundant, water–storage ponds were ubiquitous from an early date. Han dynasty (206 BCE –220 CE) grave offerings, dating as early as the first century CE, include clay models that depict irrigation ponds separated from adjacent rice fields by dikes or bunds. By the Later Han (25220 CE), some historical Chinese reservoirs had become large collectively maintained structures that occupied more than 50 hectares. The Peony Dam, built under sponsorship by the state of Chu between 608 and 586 BCE, produced a great reservoir of nearly 100 kilometers in circumference that was maintained until the Tang dynasty (618–907 CE). Small reservoirs were dug by individuals who farmed fish and turtles and grew lotuses and water chestnuts at the same time that they irrigated their own rice fields. Dams and sluice gates built into watercourses controlled the flow of water in and out of reservoirs.
All rivers carry some load of silt, or sediment suspended in water. While silt is naturally washed into rivers through processes of erosion, its quantity is exacerbated by farming and deforestation. When rivers descend quickly, their flow is turbulent and rapid, and silt remains in suspension. But when they pass slowly across flat plains, silt is deposited on riverbeds. In the absence of human settlement, rivers periodically readjust their courses across broad alluvial plains—with fertile soils and broad, shallow waters also optimized for agriculture—as their beds become full of silt and rise. The Huang (Yellow) River is the most sediment laden waterway in the world, carrying an average 1.6 billion tons of silt annually. It is an amount so great that the coastal plain at its mouth grew at a rate of 6 square kilometers per year by the 1200s and even more rapidly thereafter. Agrarian civilization emerged in the fertile loess sediment that the Huang River deposited in north China, and along with it came efforts to confine the river to a predictable course. Nevertheless, its levees, the earthen embankments that paralleled the river’s course, failed more than 1,500 times beginning in the sixth century BCE. Indeed, they were sometimes breached intentionally as the court sacrificed people to the floods in order to stop invading troops or mitigate flooding elsewhere in the system. There have also been eighteen major changes of course. Death tolls from Huang River floods are among the highest associated with any natural disasters in human history. Other rivers, such as the Miju in Yunnan, also began to flood more frequently by the mid-Ming as sedimentation followed from land clearance and deforestation, and increasingly urgent regimes of dredging and levee construction thereafter, along with conflicts over property rights and land use. As the sediment-filled riverbeds rose, people constructed ever-higher levees, which eventually towered 20 feet or more over the landscape and raised the stakes of flooding as well.
When the Huang burst its dikes in the late twelfth century, it split into multiple branch streams that ran both north and south of the Shandong peninsula. Hydrologists decided to encourage this state of affairs by removing many levees to create a broader delta and a slower watercourse. While this solution reduced the likelihood of disastrous floods, it increased total sediment buildup and the overall cost of water management. In the late sixteenth century, Pan Jixun engineered the course of the river around its confluence with the Huai and the Grand Canal to eliminate the multiple channels, force the river into a single route, and constrict the channel that remained. His activities—building 1,200,000 million feet of earthen embankment, 30,000 feet of stone embankment, and four stone spillways; dredging 115,000 feet of riverbed; stopping 139 breaches; and planting 830,000 willow trees to stabilize the tops of the dikes—served to increase the velocity of the water flow and so scour out silt at this most important junction. Even after Pan Jixun’s accomplishments, the maintenance work of dredging and diking in this vicinity required half a million workers and 800,000 ounces of silver annually; and sediment, simply deposited further downstream, remained a challenge.
Water transportation was about twenty times cheaper than overland transportation before the age of fossil fuels. In the lower Yangzi, natural watercourses and drainage and irrigation canals required few alterations to be used as transportation routes. But elsewhere massive earth-moving projects and innovations in hydrological engineering were required to create navigable waterways. The lure of long-distance commerce and travel made the outlay of labor that this involved a worthy investment. All of China’s great natural waterways flow from west to east, and canals were the lifeline linking the distinct physiographic and cultural regions of north and south China into a single, integrated empire. In 809 an imperial official named Li Ao, traveling with his pregnant wife, conducted a nine-month trip from Luoyang to Guangzhou almost entirely by water. Canals were used for transportation, drainage, sewage, mechanical power, defense, and irrigation, aims that were sometimes in competition with one another.
Transportation canals in China have a long history. The Wild Goose Canal linked the states of Song, Zhang, Chen, Cai, Cao, and Wei during the Warring States period (475–221 BCE). By 130 BCE a 124-kilometer canal terminating in the Han capital facilitated grain shipments and was used for irrigation. But the Grand Canal was the single achievement in Chinese canal building. More than 1,000 miles long, the Grand Canal allowed rice and other products of the wealthy south to support the opulent courts of the north and the vast northern armies that confronted nomad power on the steppes. It integrated all of China into a single economy, empire, and culture. To this day it is the longest canal in the world. The Grand Canal is closely associated with Emperor Sui Yangdi, who unified China in 589 after more than 300 years of warfare. Between 605 and 609, he directed efforts to link and straighten existing canals into a single system that connected the Huai to the Huang River. The Grand Canal was extended and improved during the Tang dynasty, as the court turned increasingly to the south for its supplies. When the Mongol Yuan dynasty (1279–1368) moved the capital north and east to Beijing, the canal was extended yet again. From the thirteenth to the nineteenth centuries, it remained a significant route for trade and communication, particularly the transport of the annual grain tribute from south to north. In 1793 Britain’s Macartney Embassy traveled the canal to Beijing with a crew of artists and naturalists who left a vivid record of this extraordinary waterway. Nevertheless, ecological decline set in by the turn of the nineteenth century. The system collapsed altogether by the 1820s, and in 1832 troops were needed to quell an uprising of peasants who had rallied against flooding along its disintegrating course.
Maintaining the Grand Canal inspired hydrological innovation throughout the imperial era. During the Tang, Liu Yan discovered how to manage currents and earthworks to permit the Grand Canal to meet the Huang River. Pan Jixun’s efforts to reduce silt buildup in the Huang were also directed at maintaining the Grand Canal, though some other efforts to stabilize the Canal produced unintended hydrological consequences, such as sediment buildup along
tributary streams. In the early 1700s, Zhang Pengge improved the canal’s lock mechanisms and dredging regimes to mitigate the massive floods that plagued agricultural lands along the southern part of the canal’s path.
Water Conservation and the History of China
The study of water conservation in Chinese history, at least in Western languages, is closely associated with the theories of the German-born historian and sinologist Karl Wittvogel (1896–1988), who argued that flood control was the formative activity that fostered a strong—in his words “despotic”—imperial state in China. Wittvogel overlooked many details that have become apparent to subsequent scholars. Water-control systems come in all sizes. Sometimes even the most heavily engineered of agricultural environments arose organically through centuries of small-scale collective activity with no state intervention. A great deal of water engineering was orchestrated according to local collective action, not by an authoritarian state. For instance, at the Dujiangyan waterworks in Sichuan, and at the Sangyuan polder in Guangdong, customary village associations and publicly selected representatives apportioned irrigation water among the various fields. Likewise, many constituencies needed to come together to allow the construction of Yangzi delta polders during the Song. An ambitious state in search of tax revenues, land owners seeking to increase property values, local officials seeking fame, and a growing population of civilians and military colonists eager for public works employment all played a role in water management in imperial China. All of these interests needed to be aligned for water conservation initiatives to succeed. By the Southern Song, water conservation in the lower Yangzi was funded jointly by the state and private investors, and labor was often voluntary and paid for in cash. Even the spectacular projects orchestrated from the court proceeded by trial and error, grand initiatives in one place producing unintended consequences in another.
An engineered water regime truly required not a despotic state so much as a perpetual, consultative, expensive and backbreaking commitment to the everyday maintenance of an inherently unstable and entirely artificial environment. It also required social and technological solutions for managing conflicts over priorities. The tension between the objectives of flood control, transportation, and irrigation were acute. For instance, the Huang River dikes were often breached intentionally by farmers seeking to irrigate their wheat fields. Finally, once any system was in place, it was only by dredging channels and building up earthworks that people could forestall disastrous, fatal floods. Once dense populations depended upon intensive agriculture that required water management, there was no going back.
Bracketing this critique, Wittvogel deserves credit for pioneering work on the primal role of water engineering in the development of China’s empire and civilization. He and his successors have ensured that understanding the complex systems that human intervention has brought to bear on the movement of water remains a topic at the forefront of the study of imperial China. Water conservation is crucial for exploring many topics in Chinese history, including agriculture and its intensification, labor, technology, the commercial economy, environmental history, and state power.
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Song Ching-Chang’s reconstruction of the earlier survey by Chin Chiu-Shao, paying closer attention to the reality of the geography, and adding more detail, such as the sluice-gate at the entrance to the parallel canal. The main canal runs along ½ li away from the river and takes 2½ li to reach that position. Source: Needham, Joseph, (1959). Science and Civilisation in China.
Transportation canals of all sizes have a long history in China. PHOTO BY JOAN LEBOLD COHEN.
Presentation about the Water Conservancy Project at Yangzhou, 1979. PHOTO BY JOAN LEBOLD COHEN.
Water Conservation (Shu?lì ??)|Shu?lì ?? (Water Conservation)