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●問題1：什麼是大型水壩？目前有多少大型水壩呢？
答：依據水壩業界的定義，大型水壩是指高於15公尺(高於四層樓)的水壩。全世界共有四萬多個大型水壩，其中有300多個是主要水壩，巨大到至少符合某一標準，例如高度(至少150公尺)、水庫體積或蓄水量。
●問題2：哪些國家有最多大型水壩呢？
答：中國擁有約一萬九千個大型水壩，美國排第二，擁有約五千五百個大型水壩，接著是前蘇聯、日本、印度。巴西則排第十，擁有約五百一十六個大型水壩。美國擁有最多的主要水壩，有50個，接著是加拿大，巴西則有16個.
●問題3：目前正在建造中的有多少呢？
答：大型水壩完工的速率從1950年代到1970年代中期的每年約1,000個，到1990年代早期的每年約260個。1994年初有超過1,000個大型水壩在興建，而目前擁有最多正在興建的大型水壩的國家分別是中國、土耳其、南韓、和日本。
●問題4：為什麼有這麼多的聲音反對大型水壩呢？
答：大型水壩因為許許多多的社會、環境、經濟、和安全等原因而受到反對。最主要原因是因為水壩要蓄水，而使大量的人必須遷離他們原有的的土地和家園。數百萬人的生活也會因為處在下游而受到影響，例如漁業損失，土地受污染，水量減少，還有因喪失季節性泛洪而帶來的自然養料和灌溉功能，而減少了農地和森林的肥沃度。水壩也助長了以水為媒介的傳染病，如瘧疾、萊什曼蟲病、住血吸蟲病。反對者也相信，水壩的好處通常被故意誇大，水壩所能提供的功能，也有其他更有效率和可持續性的方式可取代。
●問題5：已經有多少人因水壩而被遷移呢？
答：大約介於三千萬到六千萬人之間，大部分是在中國和印度。目前每年大約有兩百萬人因大型水壩的興建而遷移。
●問題6：因為水壩被遷移的人有受到公平的賠償嗎？
答：幾乎在每一個研究的案例中，大部分的人，通常是農夫或當地人，在經濟上變得更貧困了，受苦於文化消失，較高的疾病與死亡率，以及巨大的心理壓力。在一些案例中，居民甚至沒有，或幾乎沒有因損失而得到補償，就算有，現金也很少足夠到能補償失去的土地、家園、工作、與商機；交換給農民的土地通常是品質較差的，而且也較原來持有的土地小。
●問題7：有多少土地已因蓄水而被淹沒呢？
答：全世界已有超過四十萬平方公里，大約相當於加州面積，因蓄水而被淹沒。這約佔了全世界土地面積的0.3%；但是，損失的程度是大於數字上所能顯示的，因為這些河谷土地是世界上最肥沃的農地，最多樣化的森林與溼地生態系。
●問題8：有許多人因水壩崩潰而喪生嗎？
答：即使不把中國的200座水壩崩潰或溢頂算在內，在二十世紀還是有超過一萬三千五百人因水壩崩潰或溢頂而死亡。1975年八月，中國海南島的兩個大型水壩，因強烈颱風而破裂，約導致八萬到二十三萬人死亡；中國政府一直守住這個祕密，直到1995年才向外界揭露出來。居民也可能因大量蓄水的重量所導致的地震而死亡﹔1967年在印度，一個達6.3級的地震，使Koyma水壩殺害了約180人。
●問題9：大型水壩提供了什麼好處呢？
答：大多數的大型水壩是為灌溉而建的，幾乎所有的主要水壩則是為水利發電而建造的。世界上幾乎有五分之一的電力是由水壩提供的，水壩的功能還有控制泛洪，城市供水，和河川航行。許多水壩是多用途的，提供上述兩項或更多的好處。
●問題10：我們一定需要水壩來製造便宜且乾淨的電力嗎？
答：一旦水庫建成 -水力發電便很便宜，但問題是建造水壩的巨額經費和長期的興建過程。例如，Itaipu水壩花了兩百億美金，建造期長達十八年。水力發電水壩的實際成本幾乎總是比預計的成本要高得多，平均要高約30%。水壩設計者通常對於水壩能發多少電非常樂觀，經常忽略了乾旱所帶來的衝擊，也就是說水壩的發電量通常比預定的少。Itaipu水壩就比預計的發電量少約20%。
當這些高成本，長期拖延，還有低河川流量的風險因素被列入電力成本的計算時，我們可以了解水力發電是一種昂貴的發電方式。水力發電不被認為是乾淨的能源，因為會破壞河川生態系和產生許多社會衝擊。國際上，私人的電力計劃投資大多避免興建大型水壩，而傾向於投資較便宜且低風險的天然氣發電廠。
●問題11：大型水壩批評者支持怎樣的發電方法呢？
答：世界大部分地區的電力使用是極端的浪費，在興建新的發電廠前的第一優先考量，是提高能源供應與使用的效率﹔當新的發電廠有明確的必要性時，大部分的環境主張者傾向於使用太陽能與風力，因這些方式已接近商業化可行的邊緣﹔在這些再生能源發電方式普及以前，天然氣發電是較合乎成本效益的，而且環境衝擊遠低於燃煤或燃油發電廠。尤其在鄉村地區，小型水壩可能是可持續的、較經濟的電力來源。
●問題12：水壩是一種防止河川氾濫的有效方法嗎？
答：水壩可以防止規律性的年度性氾濫，但卻經常沒有辦法阻止例外的大洪水。因為水壩導致人們相信洪水是可以被控制的，因而泛洪平原逐漸被開發掉；當大洪水真的來時，所造成的危害經常要比沒有水壩存在要來得大。
●問題13：有其他方法供應水給農夫和城市嗎？
答：大部分大型水壩的水是供給農夫的，只有一小部份是供應到城市；通常來說，世界上的灌溉系統是非常浪費水的，因此供應城市水源最便宜、最有效方法是增加灌溉農業的效率。灌溉農業的好處總是被極度的誇大了，許多大型灌溉計畫向非常多小地主買下土地，以所謂農業經濟作物取代了傳統的農耕系統，為了供應城市和出口，而生產昂貴的農作物，增加失去土地的人和鄉村飢餓者。另外，改善城市地區供水的連結和減少浪費也是重要的。
●問題14：大型水壩的批評者反對所有的水壩嗎？
答：通常大型水壩的批評者，並不認為所有的水壩都不可以建；他們相信，只有在計畫案所有相關資訊是公開的前提之下，水壩（或其他發展計畫）才可以興建；計畫案提議者所宣稱的經濟的、環境的、還有社會的成本與效益，應該被外部獨立專家證實；並且，要在受計畫案影響人的同意之下才能興建。
原文詳見：http://www.irn.org/basics/qanda.shtml
版權歸屬 International Rivers Network，環境信託協會 (黃子晏 譯，蔡麗伶審校)
中英對照全文詳見：http://news.ngo.org.tw/issue/
water/issue-water-irn00052201.htm |
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Q. What is a large dam? How many large dams are there?
A: A large dam is defined by the dam industry as one higher than 15 metres (taller than a four-story building). There are more than 40,000 large dams worldwide. There are more than 300 major dams - giants which meet one of a number of criteria on height (at least 150 metres), dam volume and reservoir volume.
Q: Which countries have the most large dams?
A: China has around 19,000 large dams. The US is the second most dammed country with some 5,500 large dams, followed by the ex-USSR, Japan and India. Brazil is in tenth place with around 516 large dams. The US has the most major dams - 50 - followed by the ex-USSR, Canada and then Brazil with 16.
Q: How many are being built today?
A: The rate at which large dams are completed has declined from around 1,000 a year from the 1950s to the mid-1970s to around 260 a year during the early 1990s. More than 1,000 large dams were under construction at the beginning of 1994. The countries with the most large dams under construction are currently China, Turkey, South Korea and Japan.
Q: Why is there so much opposition to large dams?
A: Large dams have provoked opposition for numerous social, environmental, economic and safety reasons. The main reason for opposition worldwide are the huge numbers of people evicted from their lands and homes to make way for reservoirs. The livelihoods of many millions of people also suffer because of the downstream effects of dams: the loss of fisheries, contaminated water, decreased amounts of water, and a reduction in the fertility of farmlands and forests due to the loss of natural fertilizers and irrigation in seasonal floods. Dams also spread waterborne diseases such as malaria, leishmaniasis and schistosomiasis. Opponents also believe that the benefits of dams have frequently been deliberately exaggerated and that the services they provide could be provided by other more efficient and sustainable means.
Q: How many people have been displaced by dams?
A: Between 30 and 60 million, the majority of them in China and India. At present perhaps 2 million people are displaced every year by large dams.
Q: Aren't people displaced by dams fairly compensated?
A: In nearly every case which has been studied, the majority of people evicted - usually poor farmers and indigenous people - are further impoverished economically and suffer cultural decline, high rates of sickness and death, and great psychological stress. In some cases people receive no or negligible compensation for their losses. Where compensation is given, cash payments are very rarely enough to compensate for the loss of land, homes, jobs and businesses and replacement land for farmers is usually of poorer quality and smaller than the original holdings.
Q: How much land has been flooded under reservoirs?
A: More than 400,000 square kilometres - the area of California - have been inundated by reservoirs worldwide. This represents 0.3 percent of the world's land area, but the significance of the loss is greater than the figure suggests as river valley land provides the world's most fertile farmland, and most diverse forests and wetland ecosystems.
Q: Have many people been killed in dam collapses?
A: More than 13,500 people have been swept to their deaths by the roughly 200 dams outside China which have collapsed or been overtopped during the 20th century. Two large dams which burst when a massive typhoon hit the Chinese province of Henan in August 1975 left an estimated 80,000 to 230,000 dead. This disaster was kept secret by the Chinese government and was only revealed to the outside world in 1995. People have also died in earthquakes caused by the great weight of water in large reservoirs. A magnitude 6.3 earthquake caused by Koyna Dam in India in 1967 killed around 180 people.
Q: What are the benefits provided by large dams?
A: The majority of large dams are built for irrigation; almost all major dams are built for hydropower. Nearly one-fifth of the world's electricity is generated by dams. Dams also provide flood control, supply water to cities, and can assist river navigation. Many dams are multipurpose, providing two or more of the above benefits.
Q: Surely we need dams to produce cheap and clean electricity?
A: Hydroelectricity is cheap to produce - once the dams are built. The problem is the huge costs of building dams and the long time it takes to build them. The Itaipu Dam, for example, cost $20 billion and took 18 years to build. Actual costs for hydropower dams are also almost always far higher than estimated costs - on average around 30 percent higher. Dam designers are often very optimistic about how much power their dams will produce and often fail to account for the impacts of droughts, meaning that dams often produce less power than promised. Itaipu generates around 20 percent less electricity than predicted.
When these high costs, delays and risks of low river flows are factored into calculations of the costs of electricity it can be seen that hydropower is now an expensive form of power generation. Hydropower should not be considered as clean power because of the destruction of river ecosystems and its many social impacts. Internationally, private investors in power projects are largely avoiding large dams and prefer to invest in cheaper and less risky gas-fired power plants.
Q: What forms of power generation do large dam critics support?
A: Electricity use in most parts of the world is extremely wasteful. The priority before building new power plants should always be to improve the efficiency of existing energy supply and use. When new power plants are clearly needed, most environmentalists favor the use of solar and wind power, which are now on the verge of becoming commercially viable. Until these renewables are viable, gas-fired generation is cost-effective and has a far lower environmental impact than coal or oil-generation. Small dams can be a sustainable and economic source of electricity, especially in rural areas.
Q: Are dams an effective method of stopping flood damage?
A: Dams can stop regular annual floods but often fail to hold back exceptionally large floods. Because dams lead people to believe that floods are controlled, they lead to increased development of floodplains. When a large flood does come, damages caused are often greater than they would have been without the dam.
Q: Are there other ways of supplying water to farmers and cities?
A: Most water from large dams goes to farmers - only a very small percentage goes to cities. Irrigation systems around the world are in general very wasteful of water. The cheapest and most effective way of providing more water to cities is therefore to increase the efficiency of irrigated agriculture. The benefits of irrigated agriculture have in any case been seriously overstated - many large irrigation schemes have displaced huge numbers of small landholders and replaced traditional farming systems with agribusiness plantations producing expensive crops for cities and for export, increasing landlessness and rural hunger. Improving leakage and waste in urban water supply systems is also important.
Q: Do critics of large dams oppose all dams?
A: In general, opponents of large dams do not believe that no dam should ever be constructed. They do believe that dams (and other development projects) should only be built after all relevant project information has been made public; the claims of project promoters of the economic, environmental and social benefits and costs of projects are verified by independent experts; and when affected people agree that the project should be built. |
