Farmers in the foothills of the Zagros mountains on the eastern edge of Mesopotamia may have been the first dam builders. Eight thousand-year-old irrigation canals have been found in the area and it is not unlikely that small weirs of brushwood and earth were used to divert water from streams into the canals. By 6,500 years ago the Sumerians were criss-crossing the plains along the lower Tigris and Euphrates with networks of irrigation canals. Again no physical evidence of dams has been found from this period but it is likely that they were used to control flows of irrigation water.
The earliest dams for which remains have been found were built around 3,000 BC as part of an elaborate water supply system for the town of Jawa in modern-day Jordan. The system included a 200 metre wide weir which diverted water via a canal into ten small reservoirs impounded by rock and earth dams. The largest of the dams was more than four metres high and 80 metres long. Some 400 years later, around the time of the first pyramids, Egyptian masons constructed the Sadd el-Kafra, or 'Dam of the Pagans' across a seasonal stream near Cairo. This squat mass of sand, gravel and rock was 14 metres high and 113 metres long, and retained by some 17,000 cut stone blocks. After perhaps a decade of construction, but before it could be completed, the dam was partly washed away and was never repaired. The failed dam may been intended to supply water to local quarries. Because the Nile's floods inundated their fields before the planting season each year, the farmers of Ancient Egypt did not need dams for irrigation.
ancient dam built in the Middle East hundreds of years ago.
Courtesy: A Sergeev
By the late first millennium BC, stone and earth dams had been built around the Mediterranean, in the Middle East, China, and Central America. The ingenuity of Roman engineers is perhaps most visible in their dams and aqueducts. The most impressive surviving Roman dams are in Spain which continued to be preeminent in hydraulic engineering through the Moorish period and into modern times. A 46-metre-high stone dam near Alicante begun in 1580 and completed 14 years later was the highest in the world for the better part of three centuries.
South Asia, too, has a long history of dam building. Long earthen embankments were built to store water for Sri Lankan cities from the 4th century BC. One of these early embankments was raised in 460 AD to a height of 34 metres and was the world's highest dam for more than a millennium later. King Parakrama Babu, a 12th century Sinhalese ruler notorious as a tyrant and megalomaniac, boasted to have built and restored more than 4,000 dams. One old embankment he enlarged to a height of 15 metres and an incredible length of nearly 14 kilometres. No dam equalled it in volume until the early 20th century. Parakrama Babu's large dams, believes anthropologist Edward Leach, were of little use to most Sri Lankan villagers who relied for irrigation on small artificial ponds known as 'tanks'. The large dams, says Leach, 'are monuments, not utilitarian structures.'
Technologies to convert the energy of flowing water into mechanical energy have a history almost as long as that of irrigation. A type of waterwheel known as the Noria which has buckets around its rim to scoop up water from a river or canal was used in Ancient Egypt and Sumeria. By the first century BC, watermills were used to grind corn in Rome. The Domesday Book of 1086 records 5,624 watermills in England -- roughly one to every 250 people.
Watermills were not only built for raising water and grinding corn. During the later Middle Ages they performed numerous tasks in the great industrial centres of Germany and northern Italy including pulping rags for paper, hammering iron, beating hides in tanneries, spinning silk, crushing ores and pumping water from mines. Ores from the famous 'silver mountain' at Potosà in Bolivia were ground in well over a hundred watermills. In the early 17th century, the dam holding back one of the largest of the 32 reservoirs supplying water to the mills collapsed, washing away 4,000 people along with almost all the mills. By the beginning of the industrial revolution some half a million watermills were powering Europe's factories and mines.
Almost 200 dams higher than 15 metres were built in fast-industrializing 19th century Britain, mainly to store water for its expanding cities. In 1900, Britain had nearly as many large dams as the rest of the world put together. Nineteenth century dams were mainly earth embankments designed largely on the basis of trial and error -- until the 1930s there was little scientific understanding of how soil and rock behaved under pressure. Dam builders in the 19th century (and even today in some parts of the world) also had little streamflow or rainfall data, and few statistical tools to analyze what hydrological data had been gathered. As a consequence, their structures collapsed with alarming frequency. Two hundred and fifty people were killed when a water supply dam in Yorkshire burst in 1864. The US had a particularly bad safety record: nearly one in ten embankments built in the US before 1930 failed. More than 2,200 people were swept to their deaths when a dam above the town of Johnstown, Pennsylvania collapsed in 1889. The earthen embankment had held back the largest reservoir in the US.
French engineer Benoit Fourneyron perfected the first water turbine in 1832, hugely boosting the efficiency of watermills (a turbine, which converts the potential energy of falling water into mechanical energy, is far more efficient than a waterwheel which is powered by the kinetic energy of flowing water). The full significance of the turbine became clear in the latter part of the 19th century with advances in electrical engineering which led to the building of power stations and transmission lines. The world's first hydro plant, a run-of-river dam in Appleton, Wisconsin, began producing power in 1882. The following year hydro dams were built in both Italy and Norway.
Over the next few decades small hydro dams proliferated on the swift-flowing rivers and streams of Europe, most notably in Scandinavia and the Alps. After the turn of the century, the size of the dams and power stations being built began rapidly to increase. Progress in turbine design increased the head at which turbines could operate from 30 metres in 1900 to more than 200 metres by the 1930s, and improvements in dam engineering allowed the high dams to be built to create this head.
Extracted from: Silenced Rivers; Patrick McCully; Zed Books, 2001