【摘要】想要写出一篇优秀的雅思作文，考生要熟悉掌握不同的论证方法，这样才会更加有说服力。今天小编为大家整理了雅思写作相关话题，想要取得雅思写作高分的话，考生应练习足够的雅思话题。下面和小编一起就赶紧来学习一下吧。
(环境类与社会类满分雅思范文解析及技巧,环球网校雅思频道整理)
AThe fertile land of the Nile delta is being eroded along Egypt’s Mediterranean coast at an astounding rate，in some parts estimated at 100 metres per year.In the past，land scoured away from the coastline by the currents of the Mediterranean Sea used to be replaced by sediment brought down to the delta by the River Nile，but this is no longer happening.
B
Up to now, people have blamed this loss of delta land on the two large dams aI Aswan in the south of Egypt，which hold back virtually 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 north from Africa's interior to be deposited on the Nile delta.This continued for 7,000 years，eventually covering a region of over 22000 square kilometres with layers of fertile silt.Annual flooding brought in new, nutrient-rich soil to the delta region，replacing what had been washed away by the sea，and dispensing with the need for fertilizers in Egypt's richest food-growing area.But when the Aswan dams were constructed in the 20th century to provide electricity and irrigation，and to protect the huge population centre of Cairo and its surrounding areas from annual flooding and drought，most of the sediment with its naturaI fertilizer accumulated up above the dam in the southern， upstream half of Lake Nasser, instead of passing down to the delta.
C
Now, however, there turns out to be more to the story.It appears that the sediment-free water emerging from the Aswan dams picks up silt and 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，just before the river enters the delta，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.I'm ashamed to say that the significance of this didn't strike me until after I had read 50 or 60 studies，says Stanley in Marine Geology. There is still a lot of sediment coming into the delta，but virtually no sediment comes out into the Mediterranean to replenish the coastline. So this sediment must be trapped on the delta itself.
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