The construction of large-scale dams has long been considered a cornerstone of modern water management and energy production. Proponents argue that dams provide three essential benefits. First, they generate clean hydroelectric power, reducing reliance on fossil fuels and mitigating climate change. For example, the Hoover Dam in the United States produces enough electricity to serve over a million households annually. Second, dams create reservoirs that ensure a stable water supply for agriculture and municipal use, particularly in arid regions. This reliability supports food security and economic stability, as seen in the Colorado River Basin where water allocations are critical for seven states. Third, dams offer flood control by regulating river flow, protecting downstream communities from catastrophic inundation. The Three Gorges Dam in China, for instance, has significantly reduced the frequency and severity of floods along the Yangtze River. Given these advantages, many nations continue to invest heavily in dam construction as a rational strategy for sustainable development.
🎧 听力讲座
🎯 模拟考试环境：先点「播放讲座」听完内容，再作答。听力原文默认隐藏。
While the reading presents dams as beneficial, a closer examination reveals severe drawbacks that undermine these claims. First, hydroelectric power is not entirely clean. Reservoirs created by dams flood vast areas of vegetation, which decomposes underwater and releases methane—a greenhouse gas far more potent than carbon dioxide. Studies of tropical dams, such as the Balbina Dam in Brazil, show that their emissions can exceed those of equivalent fossil-fuel plants for decades. Second, the promise of stable water supply is misleading. Dams often lose significant water through evaporation from reservoir surfaces, especially in hot climates, and they trap sediments that would otherwise replenish downstream farmlands. This leads to reduced soil fertility and increased reliance on fertilizers, while downstream communities face water scarcity during droughts due to upstream storage. Third, flood control is a double-edged sword. By preventing small and medium floods, dams allow human settlements to expand into floodplains. When extreme floods do occur, they exceed dam capacity, causing catastrophic failures and greater damage than would have happened naturally. The 1975 Banqiao Dam collapse in China, which killed over 100,000 people, exemplifies this risk. Thus, dams often create more problems than they solve.
📝 写作提示 Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.
