Why can levees make Yellow River floods more destructive when they fail?

Levees can make flooding on the Yellow River more destructive because they artificially confine the river and elevate its bed relative to the surrounding landscape.1

Because the Yellow River carries an exceptionally high silt load, sediment settles in the channel between the levees as the water's velocity decreases. Over time, this process builds up the riverbed until it sits significantly higher than the adjacent North China Plain. In some sections, the water level is already well above the surrounding countryside even during low-water periods.123

When these levees eventually breach, the river—already perched above the land—is released with greater force and volume than it would have been in an unconfined state. This results in cataclysmic flooding that can submerge vast areas and destroy entire villages, as the water rushes out onto the lower-lying ground. Consequently, while levees are intended to provide protection, their long-term use has made channel shifts and flood events more dramatic and devastating.12