Hydrology: A Question of Birthright

• Share

(5 of 8)

Prayers & Plans. Reaction to the problems of supply — whether the difficulty stems from too much water or too little—parallels the trouble of pollution. It is always when danger is imminent and ominous that nations have buckled down to the task at hand. In The Netherlands, where three-fifths of the population lives on land reclaimed from the sea by an intricate network of dikes, dams and canals, the Dutch are now spending $830 million to throw up steel levees and floodgates to keep the sea from counterattacking. In Israel, where water scarcity is as old as the land, planning and technology have been equally dramatic.

As late as 1950, Israelis relied on wells, rain tanks and collection systems. When there was no rain, they could only pray. Now Israelis have drawn up a master plan, nationalized all water, instituted strict rationing, tapped the Sea of Galilee, and laid out a grid of modern wells, reservoirs and pipelines. So well managed is the country's water supply that nearly 90% of all possible sources are being used—and 98% of all Israelis have running water.

Hardly a drop escapes the notice of the country's watchers. When the seas begin to seep into fresh-water wells near Tel Aviv, engineers pump fresh water into rock cavities between the wells and the sea, building up a barrier against seawater intrusion. Since agriculture is Israel's heaviest user of water, Israeli scientists are systematically searching for the answer to a question that has plagued farmers throughout history: How much water does each crop actually need? Using radioactive tracer materials, American-born Soil Physicist Daniel Hillel is keeping track of irrigation water as it enters the fields and as it escapes through evaporation or plant transpiration. He radiates neutrons into the soil near plant roots and measures the results: the more water in the soil, the slower the neutrons move. He shoots leaves with beta rays to determine their water content. Going back to the same leaves daily, he keeps a record of their transpiration rate. After 200 experiments of this type, Israel has been able to reduce irrigation 20% while increasing crop yields 60%.

And still, some water gets away. Soil experts are spraying plants with anti-transpirant chemicals, usually fatty acids, to reduce the loss of water from leaves. Because more than half of most irrigation water evaporates or is absorbed by the soil before it reaches its destination, Israeli farmers are encouraged to apply a wax coating to their ditches to form a barrier against absorption. Like the ancient Nabataeans who once cultivated the desert, the Israelis also practice "runoff farming." But the Nabataeans used wadi beds as catch basins; the Israelis cut contoured strips and seal alternating strips with modern, petroleum-based chemicals. Water is caught in the sealed strip and runs off into the parallel strip where the crops are planted. "We have discovered little that is really new in water planning," says Yaacov Vardi, an Israeli water engineer. "Our success has been to take well-known theories, put them into action on a daily basis and show the world what to do with little water."