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Dams are built across rivers and other water bodies to control the flow of water. They play a crucial role in water management including flood control, irrigation, navigation, and generation of hydroelectric power. Dams store water and release it as needed according to different seasonal requirements. 1. Flood control: During the rainy season, dams collect excess water which can be gradually released, thereby mitigating the risk of floods.2. Irrigation: The water stored in dams is used for irrigating agricultural lands, especially in arid region.3. Navigation: Dams help maintain water levels in rivers making them navigable throughout the year.4. Hydroelectric power generation: The falling water from height of dams is used to rotate turbines that generate electricity.

While dams provide several benefits, they also have negative impacts on the environment and societies: 1. Impact on wildlife and aquatic life: The construction of dams alters the natural flow of rivers, affecting aquatic life. Fish migration routes can be blocked, potentially leading to decrease in fish populations.2. Alteration of ecosystems: Dams can alter the surrounding ecosystems which depend on regular flooding cycles. 3. Displacement of communities: The building of large dams often requires displacement of local communities as the reservoirs created by dams can submerge vast areas.4. Risk of Dam failure: In case of an extreme event or poor maintenance, dams can fail, leading to loss of life and property downstream.

In conclusion, while dams are helpful in managing surface waters and generating hydropower energy, they also have potential negative impacts. The decision to build a dam requires thorough consideration and planning, weighing these benefits and impacts.