Hydrology: Ask the Ancients

The kingdom of Jordan is hard at work on a peculiar problem: how to keep tourists from drowning in the desert. Such startling accidents actually do occur. Last spring, when a flash flood from a rare rainstorm roared down the Siq, a vertical-walled cleft that leads to the famous dead city of Petra, a group of French travelers was trapped, and only two out of 26 survived. Jordanian authorities are anxious to keep the tourists coming, though, and the ancient Siq, reputedly opened by Moses with the flick of a magic rod, is the most dramatic approach to Petra. It would scarcely have seemed proper to install modern water-control devices.

Archaeologists came to the rescue. They pointed out that the Nabataeans, who ruled Petra long before the Christian era, were the best hydraulic engineers of antiquity. They, too, suffered from floods racing down the Siq, and they solved the problem in a manner on which modern engineers can hardly improve. In the upper part of the Siq, before it reaches the city, they built a stone dam 45 ft. high and 140 ft. long. The dam was not designed to hold an entire flood, only to check its water and divert it into a system of guide walls and a tunnel one-quarter mile long cut through a sandstone ridge. The water was finally discharged into the comparatively broad Wadi Mataha and Wadi Musa (Valley of Moses), where it would do no damage.

Until recently, the ancient dam was a wreck, but the rest of the extraordinary system is still in good condition. The tunnel needs nothing but cleaning out. Last week repairs were well under way, guided by Engineer Oliver Fulsom of the U.S. Water Control Mission. The dam is rising once more and will eventually look just about as it did 2,000 years ago. No major improvements are contemplated; the ancient Nabataeans had thought of everything.

Talented Bedouins. A leading expert on the Nabataeans, Dr. Philip C. Hammond Jr. of Princeton Theological Seminary, is watching this operation with quiet satisfaction. The Nabataeans, he explains, were a wave of Bedouins who swept out of the Arabian Desert about 300 B.C. At first they lived by plunder, with a sideline of piracy on the Red Sea; later they saw the advantages of civilization and proved to be both talented and adaptable. They took the unpromising lands that had fallen to them —the Sinai Peninsula and the dry fringes around Palestine—and made them amazingly fruitful.

Rainfall in most of that region averages only about 5 in. per year, barely enough to support the dustiest desert vegetation. But the Nabataeans learned how to concentrate the rain, leading the water off bare plateaus and making it flow gently down narrow valleys so that it filled cisterns cut in the rock and sank into the fields enclosed in stone walls. Valleys that are now deserted except for wandering Bedouins, once supported strings of villages. The country has never been as thickly inhabited since.

Pottery Mains. The Nabataean capital, Petra, is a museum of exceptional hydraulic engineering. Besides the Siq dam and diversion system, it has a spreading network of channels cut into the rock to lead water to the city from distant springs. In one detail the Nabataeans were even ahead of the Romans. Instead of high aqueducts, they used carefully sealed pottery pipes to carry water under pressure, as modern water systems use pipes of metal.

When he hears of visiting engineers searching for water in Nabataean country, Dr. Hammond likes to point out that the tricks of modern geology can be a waste of time. The first step, he believes, should be to look for fragments of Nabataean pottery, which was remarkably thin and strong. It often leads to ruins of buildings in apparently waterless places. “But water is always available,” says Dr. Hammond. “The Nabataeans wouldn’t have built a town if they couldn’t get water for it.”