首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
The fertile land of the Nile delta is being eroded along Egypt’s Mediterranean coast at an astounding rate, in some parts estima
The fertile land of the Nile delta is being eroded along Egypt’s Mediterranean coast at an astounding rate, in some parts estima
admin
2020-12-14
17
问题
The 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 dawn 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 dams at 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, and 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 22,000 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 natural fertilizer accumulated up above the dam in the southern, upstream half of Lake Nasser, instead of passing down to the delta.
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 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."
According to Siegel, 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 principally 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 may have to be used to increase the amount of water available, "In my view, Egypt must devise a way to have more water running through the river and the delta," says Stanley. Easier said than done in a desert region with a rapidly growing population.
Which of the followings is not a purpose for the construction of Aswan dams?
选项
A、To provide electricity.
B、To supply irrigation water.
C、To promote shipping industry.
D、To protect Cairo and its surrounding areas from annual flooding.
答案
C
解析
细节题。根据第二段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“到了20世纪,人们建造了阿斯旺水坝来提供电力和进行灌溉,并保护开罗这个人口大城市及其周边地区免遭洪水和干旱”。通读选项,C选项内容“发展航运”并未提及,所以答案选C。
转载请注明原文地址:https://kaotiyun.com/show/lyP7777K
0
大学英语六级
相关试题推荐
Let’sallstopjudgingpeoplewhotalktothemselves.Newresearchsaysthatthosewhocan’tseemtokeeptheirinnermonologues
Innovation,theelixir(灵丹妙药)ofprogress,hasalwayscostpeopletheirjobs.IntheIndustrialRevolutionhandweaverswere【C1】
A、Hostingatelevisionshow.B、Reviewinganewbiography.C、Interviewingamoviestar.D、Discussingteenagerolemodels.A从选项预测本
A、Fewpopularitemscanbefoundinstores.B、Theyarenotexcitingnewarrivalsanymore.C、Youmaycompletelyforgettheproduc
A、Ignoringeverydayfastchanges.B、Learninglessonsfromworkinghard.C、Usingtheadvancedtechnologies.D、Makingothersmore
Whatifwecouldreadthemindofaterrorist?ResearchersatNorthwesternUniversityinChicagosaytheyhavetakenastepclos
TheAlzheimer’sAssociationandtheNationalAllianceforCaregivingestimatethatmenmakeupnearly40percentoffamilycare
EverydayMcDonald’sserves69mcustomers,morethanthepopulationofBritainorFrance.Thecompanyhaswhatisestimatedtob
A、Itwascanceledduetobadweather.B、Sheoversleptandmissedtheflight.C、Shedreamedofaplanecrash.D、Itwaspostponed
A、Trafficaccidents.B、Radiation.C、Traintravel.D、Aircrash.B原文提及“不久前人们认为在太空中会遭遇到严重的威胁,主要有辐射和流星撞击”。故B正确。
随机试题
A.浓缩清蛋白液B.新鲜冷冻血浆(PPP)C.浓缩血细胞D.浓缩粒细胞E.右旋糖酐
在国标中,维生素A的测定采用高效液相色谱C18反相柱分离,紫外检测器检测,采用的定量方法为
税务机关可以对下列哪些主体采取税收保全措施?()
当出货顺利结束后,跟单员在核实无误后就可以注销订单()
案例五:刘军(男)与何红(女)在1975年结婚,婚后没有生育,收养了刘军弟弟的儿子,取名刘鹏。2004年1月刘鹏娶妻王媛(女),王媛在国有公司工作,婚后刘军与何红分家,并于2005生一女刘霞。2006年刘鹏不幸因公牺牲,得到政府抚恤金20万元,王媛未再嫁而
给定资料1.政府公信力是政府依据自身的信用所获得的社会公众的信任程度,是社会组织和民众对政府信誉的一种主观价值判断,是政府实施行政行为时的形象和所产生的信誉在社会组织和民众中形成的心理反应。一句话,政府公信力是政府的影响力与号召力,体现的是政府的
习近平总书记强调,教育实践活动的主要任务要聚焦到作风建设上,集中解决()问题。
当χ→0时,下列四个无穷小中哪一个是比其它几个更高阶的无穷小量【】
窗体中有命令按钮run34,对应的事件代码如下:PrivateSubrun34_Enter()DimnumAsInteger,aAsInteger,bAsInteger,iAsIntegerFori=l
A、Heorderedapaintingforthehouse.B、Hehiredsomeonetopaintthehouse.C、Hehidinthehouse.D、Hebuiltthehouse.B
最新回复
(
0
)