TOEFL統合ライティング

📖 読解文章

The construction of large-scale dams has long been celebrated as a triumph of engineering, providing renewable energy, flood control, and irrigation. However, a growing body of evidence suggests that dams, particularly those on major river systems, pose significant ecological and social threats that outweigh their benefits. First, dams disrupt natural river flow, which is critical for the life cycles of many fish species. For example, salmon in the Pacific Northwest rely on strong seasonal currents to guide them to spawning grounds upstream. Dams slow these currents, disorienting fish and reducing their reproductive success, leading to population declines that threaten both biodiversity and local fishing economies. Second, reservoirs created by dams trap nutrient-rich sediments that would otherwise fertilize downstream floodplains. Without this natural replenishment, agricultural lands along the lower river become less productive, forcing farmers to rely on expensive chemical fertilizers that can pollute water sources. Third, the flooding of valleys behind dams displaces human communities and destroys cultural heritage sites. In many regions, indigenous peoples have lived along rivers for millennia, and their ancestral lands, burial grounds, and sacred sites are inundated, leading to irreversible loss of cultural identity and social disruption. While proponents argue that dams provide clean energy, these hidden costs—ecological, agricultural, and cultural—suggest that alternative solutions, such as wind and solar power, paired with improved water management, should be prioritized.

🎧 リスニング講義

The reading presents a rather one-sided view of dams, ignoring several counterarguments that challenge its claims. First, while dams do alter river flow, modern engineering has developed effective mitigation measures. Fish ladders and fish bypass channels, for instance, have been installed on many dams, allowing salmon and other migratory species to navigate around barriers with minimal disruption. In fact, studies show that these structures can maintain fish populations at sustainable levels when properly maintained. Second, the issue of sediment trapping is not insurmountable. Many dams now employ sediment flushing techniques, where stored water is released in controlled surges to carry accumulated sediment downstream. This practice not only restores nutrients to floodplains but also mimics natural seasonal flooding, which can benefit riparian ecosystems. Moreover, the loss of sediment can be offset by upstream soil conservation programs that reduce erosion, ensuring that reservoirs do not fill as quickly. Third, the displacement of communities is a serious concern, but it is not an inevitable consequence of dam building. In recent years, project planners have begun to conduct extensive social impact assessments and to involve affected communities in decision-making processes. Some dams are now designed with smaller footprints or located in less populated areas, and compensation and relocation programs have been improved to protect cultural heritage. For example, in some projects, historic buildings and sacred sites have been physically moved or preserved in situ. Therefore, while dams do have drawbacks, these can be managed through careful planning and technological innovation, making the reading's blanket condemnation overly pessimistic.