what are the environmental and social benefits of this dam

Previously, floods attacked the cities in the lower reaches of the Yangtze River. After this dam was built, people living in the lower reaches won't be worried about the floods. Power generation is one of the main functions of the dam. It can provide more electricity to meet the demand of the industrial development. Meanwhile, the dam area is also a popular tourist spot. And it also creates many job opportuities.

the dam has also helped the Poyang lake as the dam as increased the water levels to ensure the lake doesn't dry up again.

In 1998 flooding that would have been controlled by the dam, 4,000 died, 14 million people were left homeless and there was $24 billion in economic loss that all could have been prevented.