Final answer:
The construction along the Yangtze River that has led to population relocation, flood control, and hydroelectric power generation is the Three Gorges Dam. Completed in 2008, it's the world's largest dam and has had a significant impact on China's economy, energy production, and river transportation, despite environmental concerns and relocation controversies.
Step-by-step explanation:
The structure causing population relocation, flood control, and hydroelectric power along the Yangtze River is a dam, specifically the Three Gorges Dam. This massive project required the relocation of 1.24 million people, submerged historic villages and archaeological sites, and altered farmers' livelihoods. The dam, completed in 2008, serves multi-fold purposes: it helps control catastrophic floods that historically caused immense damage and loss of life, generates a significant amount of hydroelectric power which is crucial for China's energy needs, and improves navigation by allowing larger freight traffic. However, the construction of the Three Gorges Dam has triggered controversies due to its environmental impact and the risk of seismic activity due to its location on a fault zone.