How does sediment buildup raise the Yellow River riverbed above nearby land?

The Yellow River carries the highest concentration of silt of any river in the world, largely due to the transport of loess and the lack of vegetation to prevent erosion. As the river reaches the North China Plain, its gradient and velocity decrease significantly, causing this massive suspended load of sediment to settle and accumulate on the riverbed.12

Over time, this continuous buildup of sediment elevates the riverbed. To protect nearby agricultural regions from floods, inhabitants have constructed extensive systems of levees to confine the channel. This artificial confinement prevents the river from naturally shifting to lower ground, forcing the riverbed to rise further as more sediment is deposited within the levees. Consequently, in many sections of the lower course, the riverbed sits significantly higher than the surrounding countryside—in some areas, the high-water level can be as much as 30 to 35 feet (9 to 11 metres) above the adjacent land.12