The study looked at how the sediment in the Chongqing reach of the Yangtze River changed after the Three Gorges Reservoir was filled. They found that the amount of sediment eroded and deposited in the river bed changed over time. Initially, erosion was mainly due to upstream water and sediment, but later on, the reservoir impoundment played a bigger role. As the upstream sediment decreased, the river bed was adjusted, leading to increased erosion. This shows that the decrease in upstream sediment is a key factor in the increased erosion in the Chongqing reach.