How did levees and land reclamation contribute to flooding along the Yangtze River?

Levees and land reclamation have significantly exacerbated flooding along the Yangtze River by disrupting the river's natural ability to manage water volume and sediment.1

• Levee Construction: To protect growing populations, extensive systems of levees were built to confine the river. By restricting the Yangtze to a narrow channel, these barriers prevented the river from spreading into its natural floodplains. Consequently, sediment that would have otherwise dispersed across the land was deposited on the riverbed, causing the bottom to rise over time. This process forced flood levels to increase, making the surrounding low-lying areas more vulnerable to catastrophic breaches.123
• Land Reclamation: Historically, many lakes and wetlands served as vital natural reservoirs that absorbed excess floodwaters. Human efforts to convert these areas into cropland or cut them off from the river via levees drastically reduced the basin's capacity to store runoff. This loss of natural flood-control infrastructure, combined with deforestation that increased surface runoff, meant that the basin became less capable of handling intense monsoon rains, leading to more frequent and destructive flooding events.14