2 . The fertile land of the Nile delta is being eroded (侵蚀) along Egypt’s Mediterranean coast at an astonishing rate, in some parts estimated at 100 metres per year. In the past, land washed away from the coastline by the currents of the Mediterranean Sea used to be replaced by sediment (沉淀物) brought down to the delta by the River Nile, but this is no longer happening.
Up to now, people have blamed this loss of delta land on the two large Aswan dams in the south of Egypt, which hold back almost all of the sediment that used to flow down the river. Before the dams were built, the Nile flowed freely carrying huge quantities of sediment. But when the Aswan dams were constructed to provide electricity and irrigation, and to protect the huge population centre of Cairo from annual flooding and drought, most of the sediment with its natural fertilizer accumulated up above the dam in the southern upstream half of Lake Nasser, instead of passing down to the della.
Now, however, there turns out to be more to the story. It appears that the sediment-free water picks up sand as it erodes the river bed and banks on the 800-kilometre trip to Cairo. Daniel Jean Stanley of the Smithsonian Institute noticed that water samples taken in Cairo indicated that the river sometimes carries more than 850 grams of sediment per cubic metre of water — almost half of what it carried before the dams were built.
International environmental organizations are beginning to pay closer attention to the region, partly because of the problems of erosion and pollution of the Nile delta, but mainly because they fear the impact this situation could have on the whole Mediterranean coastal ecosystem.
But there are no easy solutions. In the immediate future, Stanley believes that one solution would be to make artificial floods to flush out the delta waterways, in the same way that natural floods did before the construction of the dams. He says, however, that in the long term an alternative process such as desalination (脱盐) may have to be used to increase the amount of water available.
1. What stopped the sediment coming down to the delta?
| A．The Mediterranean Sea. | B．The River Nile. |
| C．The Aswan dams. | D．Lake Nasser. |
2. Why were the Aswan dams built?
| A．To flush out the river beds. |
| B．To offer electricity and protection. |
| C．To make the water in the River Nile clean. |
| D．To keep the soil in the region nearby nutrient-rich. |
3. What can we infer from the third paragraph?
| A．There is no need to worry about the delta. |
| B．The methods of measurement need improving. |
| C．Whether the situation is good or not remains to be seen. |
| D．The dams’ consequences are beyond people’s expectation. |
4. What is the last paragraph mainly about?
| A．Difficulties to be settled. |
| B．Rewards for the challenge. |
| C．Severe influence of the situation. |
| D．Possible solutions to the problem. |
