Irrigation

CHINA

With China’s variable climate, relatively unpredictable rainfall, and growing population, irrigation played a crucial role in agriculture. Essentially, China was divided into two major regions, the northern half dominated by the cultivation of millet and the southern half of rice. Millet agriculture was concentrated in the vast plain of the Huang (Yellow) River. The loess soil deposited by the river from its passage across the plateau to the west provided rich and easily worked conditions, but floods from the river and its propensity to change its course were major problems. The monsoon region that had its most northerly extent in the Huai and Han River Basins and the land south to Lingnan was adapted to the cultivation of rice, a marsh grass. The monsoon, however, is unpredictable, and reticulating water from dams to the rice fields is an important means of ensuring a good harvest.

There is no compelling evidence for irrigation during the SHANG STATE (1766-1045 B. C.E.). The Shang were well able to drain wet or swampy areas with ditches or canals, as revealed through excavation at the site of Xiaotun. However, the available records indicate that it was wetter then than now, and the ORACLE BONES and other texts suggest that fields were drained and the Shang rulers had a consistent interest in opening new land to millet cultivation.

During the western zhou dynasty (1045-771 B. C.E.) inscriptions were commonly cast into bronze vessels. These form a vital contemporary source of historic information, a source that is constantly expanding with archaeological research. The bronze vessel known as the Qiu Wei ding was cast during the reign of King Gong (c. 917-900 B. C.E.). Its text incorporates one of the earliest Chinese references to a dispute over land and describes “King Gong’s irrigation works at the two Rong rivers.”

Further early records for irrigation are from the Spring and Autumn period (722-476 B. C.E.). These described the construction of the Shao reservoir in northern Anhui province under the rule of King zhuang of CHU (r. c. 612-591 b. c.e.). This facility had five water gates to receive and distribute water from the tributaries of the Huai River, to maintain a steady supply to the rice fields. It was said that 1 million mu of land was irrigated from this reservoir. It is difficult to determine the precise area of a mu, but it is thought to have measured about 100 by 100 paces, or just less than one hectare. In a second system of extensive irrigation, water was taken from the Zhang River during the reign of Marquis Xiang of WEI (424-387 B. C.E.) to reduce salinization in the rice and millet fields.

In 316 B. C.E. the qin state defeated the kingdom of SHU in Sichuan and set about improving its agricultural production. The first task was to redistribute land to new settlers on the basis of strictly ordered rectangular parcels within raised footpaths. The Min River flows southwest of Chengdu before its confluence with the Chang (Yangtze), and was prone to flooding. This problem, linked with the need to irrigate the new rice fields, led to the construction by Li Bing (306-251 b. c.e.) of the Dujiangyan dam on the Chengdu Plain, an irrigation project that exists to this day after a history of 2,300 years of continuous use. State intervention by the Qin in infrastructure projects such as major irrigation works continued to the end of the dynasty, and the massive Dujiangyan project has been described as the largest engineering work yet seen in the eastern half of Eurasia.

During the Han dynasty, China witnessed a massive increase in population and a period of relative peace after the drawn-out warfare that characterized the preceding WARRING STATES PERIOD (475-221 b. c.e). Iron could now be applied to increasing agricultural production and providing the tools necessary to complete large engineering works. The Han Chinese have left a large corpus of records that describe the widespread application of irrigation to agriculture. Essentially, this had three objectives that varied with the local conditions. One was to introduce water into the fields by means of canals and dams, another was to drain swampy land to create fields, and the third was to reduce salinization. This knowledge is nowhere better illustrated than in a memorandum prepared by Jia Rang in 7 B. C.E. for the emperor Aidi (26-1 B. C.E.). He wrote that not digging canals had three detriments, and digging them had three benefits. Problems issuing from the lack of irrigation and flood-control measures meant that people suffered from the humidity as floodwater evaporated and the soil turned alkaline. This meant that grain did not flourish. The benefits of irrigation included the washing out of salts from the fields, the spreading of silt to increase soil fertility, and the increase in production fivefold on high ground and 10-fold in low-lying terrain. Finally, with canals, heavy goods could be more easily transported.

A memorandum of the second century C. E. named the principal components of an Eastern Han irrigation system. The yanzhu was the reservoir, and the fang the dike beside the reservoir. A sui was the channel at the top of the field that distributed water, and a gui drained water away from the field when necessary. The contemporary texts of the Han are virtually unanimous in describing the increased agricultural efficiency that resulted from irrigation works. The History of the Later Han Dynasty (hou hanshu) recorded that in 36 c. e. there had been little rain in Gansu, but officials repaired the irrigation works, and everyone prospered as a result. In 90 c. E. the grand administrator Lu Bei had canals dug in Dong commandery, and the people became very wealthy Ma Yuan was a great military commander responsible for conquering the DONG SON people of the Hong (Red) River Delta in modern Vietnam in the mid-second century c. e. It is recorded that he also dug irrigation canals for the benefit of the people.

KOREA

Rice cultivation in Korea was beyond doubt introduced from china and was the mainstay of the SHILLA and PAEKCHE states in the south of the peninsula. By the fourth century, the agricultural system of china had developed considerable sophistication, involving the diversion of rivers into canals and reticulation into rice fields. Iron agricultural tools, such as the wooden spade and hoe tipped with iron, were also manufactured. This technology was applied to Korean agriculture where ponds developed for irrigation were linked with canal systems. Korea also became a conduit for the spread of this knowledge into Japan during the fifth century c. e.

Irrigation in Korea was instituted at least by the period of chinese Han settlement, when reservoirs for feeding water to rice fields were constructed. During the subsequent period of Three Kingdoms, royal and aristocratic landowners sought to increase production. Extensive irrigation was undertaken, for example, during the reign of King Chijung of Shilla (r. 500-514 C. E.), together with the use of plow oxen. Slightly later, an inscription dating to 536 C. E., during the reign of King Pophung, described construction of the “luxuriant dike” as part of an irrigation facility It had a long life, for in 798 c. e. another text described the undertaking of repairs. It must have been a major project, as it involved 136 ax men and 14,140 soldiers.

JAPAN

Rice cultivation began in Japan during the first millennium B. C.E, probably imported from established agricultural communities in Korea. The earliest agricultural villages, ascribed to the yayoi culture (300 B. C.E.-300 C. E.), already practiced a developed form of rice cultivation involving the creation of small bunded fields. Many such fields were covered by flood deposits and have been investigated by archaeologists. It is clear that they involved irrigation and drainage ditches. With the application of iron technology, also obtained at about the same time from the mainland, agricultural tools were forged to facilitate earth moving. This made it possible, for example, not only to build massive mounded tombs, the largest of which covered 60 hectares (150 acres) and was ringed by three moats, but also to create irrigation facilities. Evidence for irrigation late in the Yayoi period has been discovered through excavations on the Nara Plain, where six-meter (19.8-ft.)-wide irrigation ditches up to 1.5 meters (4.95 ft.) deep have been identified. The yamato state, which lasted from about 300 to 700 C. E., was led by powerful military rulers whose courts relied ultimately on the production of rice surpluses. Kings therefore paid particular attention to agriculture, and the NIHONGI, an early eighth-century history text, records instances of royally inspired irrigation works, such as the diversion of the Ishiwara River into a canal to carry water to thousands of hectares of formerly marginal land. This was undertaken by King Nintoku in the early fifth century. Archaeological verification of such endeavors is also seen in the Furuichi Canal of the Osaka Plain, where a 10-kilometer (6 mi.) canal between 8.5 and 9.5 meters wide has been identified. King NINTOKU (313-99 C. E.), who was interred in the largest known kofun, or burial mound, also attracted Korean workers to help in the construction and maintenance of his projects. This system may well have been instrumental in the adoption of a range of iron agricultural tools to the construction of irrigation facilities, some of which were interred in rich tombs of the period.

The late Yamato state and the nara state (710-794 C. E.) saw a marked intensification in central control over the populace at large. Legal codes prescribed the social position of every individual, from the highest minister to the lowest slave. Under the conditions of the Yoro Code of 718 C. E., the central ministries that operated under an autocratic imperial regime included one responsible for irrigation matters. The peasant farmers were allocated land, the amount varying with the composition of each household, in which people were counted from the age of six years. The allocation was reviewed every six years. These rice farmers paid a tax in kind to the state but otherwise enjoyed an element of personal freedom on their plots of land. Since the irrigation systems were state owned and controlled, however their freedom of action was strictly limited.

INDIA

That India has a long history of irrigation to improve agricultural production is evident from the description of canal excavation and bringing water to low-lying areas contained in the Vedas, the corpus of sacred hymns dating back into the second or even third millennia B. C.E. Identifying archaeological evidence for such irrigation works is not straightforward, although Gregory Possehl has suggested that irrigation may have been in place by the AMRI-NAL phase of the INDUS VALLEY CIVILIZATION (3200-2600 B. C.E.). In the case of Baluchistan, irrigation probably took the form of diverting mountain streams onto the extensive river terraces. On the Indus plains, however, it is more likely that river floods, reaching out over the extensive flood plains encouraged the sowing of wheat and barley, with the harvest proceeding as the waters receded. In southern India, tanks and canals were employed. KAUTILYA, who composed his ARTHASASTRA in the late fourth century B. C.E., was well aware of the importance of tracts with an assured water supply and the possibility of double cropping. He mentions the cultivation of rice, wheat, barley, millet, beans, and a wide range of other vegetables, herbs, and spices. Irrigation was also encouraged as a means to further reliable returns and increase the wealth of the state. One of the best examples of irrigation comes from the dam constructed during the Mauryan period on Lake Sudarsana near Juna-gadh during the reign of candragupta (325-297 B. C.E.). This was maintained over many centuries, for it was restored in the fifth century C. E. by the local governor during the reign of King Skandagupta. Indeed, irrigation works were widely applied during the Gupta empire as part of state concern for increasing production.

CENTRAL ASIA

The arid terrain that characterizes so much of the ancient SILK ROAD from the MERV (modern Mary) oasis to the TARIM BASIN is crossed by a series of rivers, of which the Amu Dar’ya and Syr Dar’ya are particularly notable. Irrigation there was a vital component to the development of states. Already by the fifth and early fourth millennia B. C.E., the oasis region that is now Turkmenistan had attracted agricultural settlements in which barley and wheat were cultivated on the basis of an irrigation system. Canals in the region of ALTYN TEPE reached many kilometers in length. Four thousand years passed before the BACTRIAN GREEK rulers instituted irrigation schemes. The Sogdians grew wealthy on their irrigation agriculture and control of trade along the Silk Road, while the KUSHAN kings expended much effort into the provision of irrigation works. Major canals and the expansion of agriculture in the Amu Dar’ya, the Tashkent, and Samarqand oasis regions led to the foundation of new urban settlements, while a vast area was brought under irrigation in KHWARIZM, the region centered on the lower reaches of the Amu Dar’ya. Here, a fully integrated system was established, with major canals taking water from the river and feeding minor distributaries. One such canal was more than 90 kilometers (54 mi.) long.

SRI LANKA

Although Sri Lanka enjoys a continually high temperature, there is considerable regional diversity in the amount and seasonal distribution of rainfall. Whereas the southern parts of the island receive up to 3,750 millimeters (150 in.) of rainfall per annum, the northern dry zone has only 750 to 1,750 millimeters (30 to 70 in.) a year, and the rain concentrates in the period of the northeast monsoon, from November to January Droughts can then persist for more than three months. Under the development of an urban civilization, such as that of anuradhapura, this rainfall pattern encourages systems of water control to ensure a predictable rice harvest. The early irrigation system that developed in the dry zone is regarded as one of the most innovative and sophisticated in the preindustrial world. The earliest inscriptions, dating from the third century B. C.E., mention small-scale irrigation, and the enlargement of the system was facilitated by the invention of the cistern sluice, known as the bisokotuva, which regulated the flow of water from a large reservoir or tank without endangering weirs. One of the major early achievements was the diversion of the Ambanganga River, a tributary of the Mahavali, which originates in the wet central highlands south of Anuradhapura.

The Alisara Canal, first mentioned during the reign of King Vasabha (65-109 C. E.), flowed for about 50 kilometers (30 mi.) to the capital. This king is credited with a marked expansion of the system, including not only the canal, but also 12 reservoirs. Between 164 and 192 C. E. two new sorts of reservoirs are named in the inscriptions: mahavavi (large) and danavavi (service) reservoirs. This period saw the development of interlinked irrigation systems. During the next century and under the reign of Mahasena (274-301 c. E.) the giant reservoir known as Minneriya was constructed. This, together with new canals and reservoirs representing a massive investment of labor, put much marginal land into production. King Dha-tusena (455-73) further added to the infrastructure of irrigation. He had a dam constructed over the Mahavali River to harness a greater supply of water and further extended the irrigated area in the western part of the dry zone. An idea of the skill of the hydraulic engineers of this period is gained from the Kalavava reservoir. The dam across the Kala River was made of tightly fitting blocks of granite, the wall being more than five kilometers (3 mi.) long and standing to a height of 12 meters. The Jayaganga canal is 80 kilometers (48 mi.) long and carried water to Anuradhapura as well as irrigated an area of 62,000 hectares (155,000 acres). The gradient for much of its length involved a fall of only 10 centimeters (4 in.) per kilometer. The Manar region in northwestern Sri Lanka is particularly dry, and here Dhatusena had a further massive dam constructed, with a length of 11 kilometers (6.6 mi.). It was then linked with distribution canals that supplemented the water supply in numerous village tanks. Many further dams and canals were constructed so that, by the 10th century, the system covered most of the dry zone and the area of Rohana in the southeast of the island. In this last region, the initiative was taken more by local communities than by the king.

The Sri Lankan irrigation system supported the great urban center of Anuradhapura as well as the second center of Polonnaruva and myriad rural villages. The social correlates of this system are a vital issue in understanding the Sri Lankan civilization of the first millennium c. e. Was it, for example, under the central control of the court and thus an example of overarching central power and authority, or was it devolved to local administration and fragmented ownership of water rights?

Some reservoirs were owned privately, by vapi-hamikas. Others were communally owned, in some cases by monasteries. Thus, the Alahara Canal was granted to a monastic foundation shortly after its completion. The king was the principal owner and beneficiary of the canals, reservoirs, and tanks, but they could also be sponsored by or given to individuals. Water was subject to tax, and a vapi-hamika was one who owned and charged for the water passing through his facility Owners also received a proportion of the production from irrigated land, known as the water share, or dak-abaka. Entrepreneurs could take a share of profit without producers being alienated from their land. This made it possible to raise two to three crops a year in extensive tracts. Again, the control of land improved by major irrigation works gave rulers considerable economic and political power.