Rainfall is not completely absent in desert areas, but it is highly variable. An annual rainfall of four inches is often used to define the limits of a desert. The impact of rainfall upon the surface water and groundwater resources of the desert is greatly influenced by landforms. Flats and depressions where water can collect are common features, but they make up only a small part of the landscape.
Arid lands, surprisingly, contain some of the world’s largest river systems, such as the Murray-Darling in Australia, the Rio Grande in North America, the Indus in Asia, and the Nile in Africa. These rivers and river systems are known as "exogenous" because their sources lie outside the arid zone. They are vital for sustaining life in some of the driest parts of the world. For centuries, the annual floods of the Nile, Tigris, and Euphrates, for example, have brought fertile silts and water to the inhabitants of their lower valleys. Today, river discharges are increasingly controlled by human intervention, creating a need for international river-basin agreements. The filling of the Ataturk and other dams in Turkey has drastically reduced flows in the Euphrates, with potentially serious consequences for Syria and Iraq.
The flow of exogenous rivers varies with the season. The desert sections of long rivers respond several months after rain has fallen outside the desert, so that peak flows may be in the dry season. This is useful for irrigation, but the high temperatures, low humidities, and different day lengths of the dry season, compared to the normal growing season, can present difficulties with some crops.
Regularly flowing rivers and streams that originate within arid lands are known as "endogenous." These are generally fed by groundwater springs, and many issue from limestone massifs, such as the Atlas Mountains in Morocco. Basaltic rocks also support springs, notably at the Jabal Al-Arab on the Jordan-Syria border. Endogenous rivers often do not reach the sea but drain into inland basins, where the water evaporates or is lost in the ground. Most desert streambeds are normally dry, but they occasionally receive large flows of water and sediment.
Deserts contain large amounts of groundwater when compared to the amounts they hold in surface stores such as lakes and rivers. But only a small fraction of groundwater enters the hydrological cycle—feeding the flows of streams, maintaining lake levels, and being recharged (or refilled) through surface flows and rainwater. In recent years, groundwater has become an increasingly important source of freshwater for desert dwellers. The United Nations Environment Programme and the World Bank have funded attempts to survey the groundwater resources of arid lands and to develop appropriate extraction techniques. Such programs are much needed because in many arid lands there is only a vague idea of the extent of groundwater resources. It is known, however, that the distribution of groundwater is uneven, and that much of it lies at great depths.
Groundwater is stored in the pore spaces and joints of rocks and unconsolidated (unsolidified) sediments or in the openings widened through fractures and weathering. The water-saturated rock or sediment is known as an "aquifer". Because they are porous, sedimentary rocks, such as sandstones and conglomerates, are important potential sources of groundwater. Large quantities of water may also be stored in limestones when joints and cracks have been enlarged to form cavities. Most limestone and sandstone aquifers are deep and extensive but may contain groundwaters that are not being recharged. Most shallow aquifers in sand and gravel deposits produce lower yields, but they can be rapidly recharged. Some deep aquifers are known as "fossil waters. The term "fossil" describes water that has been present for several thousand years. These aquifers became saturated more than 10,000 years ago and are no longer being recharged.
Water does not remain immobile in an aquifer but can seep out at springs or leak into other aquifers. The rate of movement may be very slow: in the Indus plain, .
Paragraph 1: Rainfall is not completely absent in desert areas, but it is highly variable. An annual rainfall of four inches is often used to define the limits of a desert. The impact of rainfall upon the surface water and groundwater resources of the desert is greatly influenced by landforms. Flats and depressions where water can collect are common features, but they make up only a small part of the landscape.
1. Which of the following statements about annual rainfall can be inferred from paragraph 1?
○Flat desert areas receive more annual rainfall than desert areas with mountains.
○Areas that receive more than four inches of rain per year are not considered deserts.
○Many areas receive less than four inches of annual rainfall, but only a few are deserts.
○Annual rainfall has no impact on the groundwater resources of desert areas.
Paragraph 2: Arid lands, surprisingly, contain some of the world’s largest river systems, such as the Murray-Darling in Australia, the Rio Grande in North America, the Indus in Asia, and the Nile in Africa. These rivers and river systems are known as "exogenous" because their sources lie outside the arid zone. They are vital for sustaining life in some of the driest parts of the world. For centuries, the annual floods of the Nile, Tigris, and Euphrates, for example, have brought fertile silts and water to the inhabitants of their lower valleys. Today, river discharges are increasingly controlled by human intervention, creating a need for international river-basin agreements. The filling of the Ataturk and other dams in Turkey has drastically reduced flows in the Euphrates, with potentially serious consequences for Syria and Iraq.
2. The word “drastically” in the passage is closest in meaning to
○obviously
○unfortunately
○rapidly
○severely
3. In paragraph 2, why does the author mention the Ataturk and other dams in Turkey?
○To contrast the Euphrates River with other exogenous rivers
○To illustrate the technological advances in dam building
○To argue that dams should not be built on the Euphrates River
○To support the idea that international river-basin agreements are needed
4. According to paragraph 2, which of the following is true of the Nile River?
○The Nile's flow in its desert sections is at its lowest during the dry season
○The Nile's sources are located in one of the most arid zones of the world
○The Nile's annual floods bring fertile silts and water to its lower valley
○The Nile's periodic flooding hinders the growth of some crops
Paragraph 5: Deserts contain large amounts of groundwater when compared to the amounts they hold in surface stores such as lakes and rivers. But only a small fraction of groundwater enters the hydrological cycle—feeding the flows of streams, maintaining lake levels, and being recharged (or refilled) through surface flows and rainwater. In recent years, groundwater has become an increasingly important source of freshwater for desert dwellers. The United Nations Environment Programme and the World Bank have funded attempts to survey the groundwater resources of arid lands and to develop appropriate extraction techniques. Such programs are much needed because in many arid lands there is only a vague idea of the extent of groundwater resources. It is known, however, that the distribution of groundwater is uneven, and that much of it lies at great depths.
5. The word “dwellers” in the passage is closest in meaning to
○settlements
○farmers
○tribes
○inhabitants
6. Paragraph 5 supports all of the following statements about the groundwater In deserts EXCEPT:
○The groundwater is consistently found just below the surface
○A small part of the groundwater helps maintain lake levels
○Most of the groundwater is not recharged through surface water
○The groundwater is increasingly used as a source of freshwater
Paragraph 6: Groundwater is stored in the pore spaces and joints of rocks and unconsolidated (unsolidified) sediments or in the openings widened through fractures and weathering. The water-saturated rock or sediment is known as an "aquifer". Because they are porous, sedimentary rocks, such as sandstones and conglomerates, are important potential sources of groundwater. Large quantities of water may also be stored in limestones when joints and cracks have been enlarged to form cavities. Most limestone and sandstone aquifers are deep and extensive but may contain groundwaters that are not being recharged. Most shallow aquifers in sand and gravel deposits produce lower yields, but they can be rapidly recharged. Some deep aquifers are known as "fossil waters. The term "fossil" describes water that has been present for several thousand years. These aquifers became saturated more than 10,000 years ago and are no longer being recharged.
7. The word “fractures” in the passage is closest in meaning to
○streams
○cracks
○storms
○earthquakes
8. According to paragraph 6, which of the following statements about aquifers in deserts is true?
○Water from limestone and sandstone aquifers is generally better to drink than water from sand and gravel aquifers
○Sand and gravel aquifers tend to contain less groundwater than limestone or sandstone aquifers
○Groundwater in deep aquifers is more likely to be recharged than groundwater in shallow aquifers
○Sedimentary rocks, because they are porous, are not capable of storing large amounts of groundwater
9. According to paragraph 6, the aquifers called fossil waters
○contain fossils that are thousands of years old
○took more than 10,000 years to become saturated with water
○have not gained or lost any water for thousands of years
○have been collecting water for the past 10,000 years
Paragraph 7: Water does not remain immobile in an aquifer but can seep out at springs or leak into other aquifers. The rate of movement may be very slow: in the Indus plain, the movement of saline (salty) groundwaters has still not reached equilibrium after 70 years of being tapped. The mineral content of groundwater normally increases with the depth, but even quite shallow aquifers can be highly saline.
10. The word “immobile” in the passage is closest in meaning to
○enclosed
○permanent
○motionless
○intact
11. The passage supports which of the following statements about water in the desert?
○The most visible forms of water are not the most widespread forms of water in the desert.
○Groundwater in the desert cannot become a source of drinking water but can be used for irrigation.
○Most of the water in the desert is contained in shallow aquifers that are being rapidly recharged.
○Desert areas that lack endogenous or exogenous rivers and streams cannot support life.
Paragraph 4: Regularly flowing rivers and streams that originate within arid lands are known as "endogenous." These are generally fed by groundwater springs, and many issue from limestone massifs, such as the Atlas Mountains in Morocco. Basaltic rocks also support springs, notably at the Jabal Al-Arab on the Jordan-Syria border. ■Endogenous rivers often do not reach the sea but drain into inland basins, where the water evaporates or is lost in the ground. ■Most desert streambeds are normally dry, but they occasionally receive large flows of water and sediment. ■
Paragraph 5: Deserts contain large amounts of groundwater when compared to the amounts they hold in surface stores such as lakes and rivers. ■But only a small fraction of groundwater enters the hydrological cycle—feeding the flows of streams, maintaining lake levels, and being recharged (or refilled) through surface flows and rainwater. In recent years, groundwater has become an increasingly important source of freshwater for desert dwellers. The United Nations Environment Programme and the World Bank have funded attempts to survey the groundwater resources of arid lands and to develop appropriate extraction techniques. Such programs are much needed because in many arid lands there is only a vague idea of the extent of groundwater resources. It is known, however, that the distribution of groundwater is uneven, and that much of it lies at great depths.
12. Look at the four squares [■] that indicate where the following sentence could be added to the passage
These sudden floods provide important water supplies but can also be highly destructive.
Where would the sentence best fit?
13. Directions: Select from the seven sentences below, the two sentences that correctly characterize endogenous rivers and the three sentences that correctly characterize exogenous rivers. Drag each sentence you select into the appropriate column of the table. Two of the sentences will NOT be used. This question is worth 3 points.
Endogenous Rivers
●
●
Exogenous Rivers
●
●
●
Answer Choices
○Their water generally comes from groundwater springs.
○Their water is saltier than the water of most other rivers.
○They include some of the world's largest rivers.
○They originate outside the desert.
○They often drain into inland basins and do not reach the sea.
○They contain too much silt to be useful for irrigation.
○Their water flow generally varies with the season of the year.
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參考答案：
1. ○2
2. ○4
3. ○4
4. ○3
5. ○4
6. ○1
7. ○2
8.○2
9. ○3
10. ○3
11. ○1
12. ○3
13. ○Endogenous Rivers：Their water generally; They often drain
○Exogenous Rivers：They include some; They originate outside; Their water flow
:沙漠中的水源
沙漠中并不是完全沒有降雨，只不過變數(shù)很大。通常年降水量100毫米以下是界定沙漠地區(qū)的條件。降水對沙漠地區(qū)地表和地下水資源的影響很大程度上取決于地貌。平原和洼地的共同特征是水源聚集，但是它們在地貌中所占比重很小。
令人驚奇的是，一些世界最大的河系都位于干旱地區(qū)，例如澳大利亞的墨累-達(dá)令河、北美洲的格蘭德河、亞洲的印度河以及非洲的尼羅河。這些河流及河系因?yàn)樵搭^位于干旱地區(qū)以外而被稱為“外流河”。對世界上一些最干旱地區(qū)來說，它們哺育生命，意義重大。例如，幾個(gè)世紀(jì)以來，尼羅河、底格里斯河和幼發(fā)拉底河每年都會(huì)泛濫洪水會(huì)為下游低洼地帶的居民帶來大量肥沃的泥沙和水源�，F(xiàn)在，河水流量越來越多的受到人類的干預(yù)，因而有必要簽署國際性的河流流域協(xié)議。阿塔圖爾克大壩以及土耳其境內(nèi)的其它大壩的蓄水極大地減少了幼發(fā)拉底河的徑流量，可能會(huì)給敘利亞和伊拉克帶來嚴(yán)重后果。
“外流河”的徑流量通常受季節(jié)影響。雨季過后，從外部流入沙漠區(qū)域的長河可以持續(xù)好幾個(gè)月，以便洪峰可以出現(xiàn)在旱季。這雖然利于灌溉，但是高溫度、低濕度，加上旱季獨(dú)特的晝長，相比正常生長季節(jié)依然很難種植一些農(nóng)作物。
通常發(fā)源于干旱地區(qū)的河流和溪水被稱為“內(nèi)陸河”。它們主要是由地下水泉補(bǔ)給,很多出口來自石灰?guī)r斷層，例如摩洛哥的阿特拉斯山脈。玄武巖同樣可以提供地下水泉，最具代表性的是約旦和敘利亞邊界的Jabal Al-Arab河.內(nèi)陸河通常都不能流入大海而是注入內(nèi)陸盆,蒸發(fā)掉或者消失在地表。大多數(shù)沙漠河床通常都是干涸的，但偶有較大徑流和沉積物。
相比于湖泊和河流等地表水，沙漠中地下水的貯藏量要大得多。不過只有一小部分地下水參與了水循環(huán)——補(bǔ)給河流徑流量，維持湖泊水位，并通過地表徑流和降雨進(jìn)行再次補(bǔ)給（再注入）。近些年來，地下水作為沙漠住民的淡水來源，重要性日益突顯。美國國家環(huán)境總署和世界銀行開始撥款著手調(diào)查干旱地區(qū)的地下水資源并開發(fā)合適的開采技術(shù)。這些項(xiàng)目非常有必要，因?yàn)樵诤芏喔珊档貐^(qū)對于地下水資源的程度概念非常模糊。然而可以確定的是，地下水資源分布非常不均勻，且大部分埋藏較深。
地下水一般貯存于巖石孔隙、節(jié)理、松散沉積物或者斷裂和風(fēng)化作用形成的孔洞。飽含水的巖石或沉積物被稱為“蓄水層”。因?yàn)槌练e巖多孔，比如砂巖和礫巖，都是地下水的重要潛在源頭。只要節(jié)理和裂縫擴(kuò)大形成容器，石灰?guī)r中也能夠儲(chǔ)存大量水資源。大部分石灰?guī)r和砂巖蓄水層深廣，但是儲(chǔ)存的水資源不可再生。大多數(shù)沙石中較淺的蓄水層貯水量少，但可以迅速再生。一些深層地下水被稱作“化石水”。用“化石”來形容水，這就意味著這些水已經(jīng)存在了千年之久。這些蓄水層注滿水起碼已經(jīng)1萬年以上了，而其無法再生。
貯存在蓄水層的水并非不流動(dòng)，而是會(huì)通過泉眼滲出或是進(jìn)入其他蓄水層，可以流動(dòng)水的比例可能很低：在印度河平原，流動(dòng)的含鹽地下水在開采了70年之后依舊不能達(dá)到平衡。正常情況下,地下水的礦物含量隨著深度的增加而增加，，但是即使很淺的蓄水層中可能含鹽量也很高。
阿特拉斯山脈（阿爾卑斯山系的一部分）
節(jié)理：巖石中的裂隙，其兩側(cè)巖石沒有明顯的位移。地殼上部巖石中最廣泛發(fā)育的一種斷裂構(gòu)造。
