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20 September 2004
The world's oldest dam

The first dam in history is clearly a major engineering achievement. But it is also something of a disaster story. Dating back some 4000 years ago, and estimated to have been between 10 and 15 years in the making, Sadd Al-Kafara was destroyed by heavy rainfall soon after its completion. The experience was so traumatic for the Ancient Egyptians, that they never tried to build a dam again.
     "This is the first known instance of a stone dam to be constructed across a river anywhere in the world. I'm surprised that so little is known about it," said  John Broad, a retired consulting engineer with a passionate interest in ancient structures. According to the records, the dam is situated between Wadi Al-Hof and Wadi Al-Garawi, some 25 kilometres south of Cairo.
     When Sadd Al-Kafara was discovered in 1885 by the German archaeologist G.Schweinfurth, he calculated that it had been necessary to excavate and transport approximately 100,000 cubic metres of rock and rubble for its construction. Schweinfurth also established that the central section of the dam was missing. "That turned out to be a mixed blessing," Broad said, "because although the structure was no longer complete, the fact the middle was missing exposed cross sections of the remaining parts of the dam. So it was possible to study its construction."
     The dam was built straight across Wadi Al-Garawi at a point where the valley narrows to about 100 metres wide. The floor was covered with gravel and boulders of various sizes. Here and there was a thin veneer of alluvium, cracked by the heat where it was not held together by soil-binding desert plants. The sloping outer faces, according to existing records, are about 13 metres wide at the top, and 24 metres at the base, the space between the two walls being filled with rubble. It must have been an impressive structure before the whole of the central part, covering a width of about 36 metres, was washed away. No mortar was used, as it was not considered to be a sealing material in ancient times.
     "The Ancient Egyptians lacked experience in sealing the dam face and its base against the percolation of water through and under the dam," Broad explained. "This water gradually eroded larger cavities and pathways until the increasing rush of water caused the dam to collapse. It is not known if a spillway was provided; that would have allowed excess water to pass safely over the top of the dam. In all likelihood it was not, and the overspill from the full dam caused erosion on the downstream side which led to its collapse."
     The dam has now been authoritatively dated to the Third or Fourth Dynasties (between 2686 and 2498 BCE).

Source: Al Ahram (16 September 2004)

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