Efforts to prevent the Yellow River flooding may have made it worse

Analysis of floods in China’s Yellow River suggests that mud barriers meant to keep floods out resulted in more frequent floods

To Carissa Wong

An analysis of floods from the Yellow River in China shows that building mud walls along rivers to prevent flooding can have the opposite effect.

Extreme and frequent rainfall due to global warming means that the threat of river flooding is increasing for millions of people around the world. Much research has been done on how climate change affects flood risk, but the role of human activity is less clear.

To investigate this, Shi-Yong Yu of Jiangsu Normal University, China, and his colleagues analyzed the frequency of flooding in the Yellow River in northern China. This 800-kilometer-long waterway was the cradle of ancient Chinese civilization between 4,100 and 3,600 years ago.

Researchers used historical records and data from river sediments to compile a timeline of river flooding over the past 12,000 years. They found that between 12,000 and 7,000 years ago, floods were rare, averaging only four floods every 100 years.

They then compared flood timelines with records of human activities such as agriculture, and found that floods became more common after the expansion of human settlements in the region about 4,000 years ago.

In particular, the analysis revealed a significant increase in flood rates around 1,500 years ago when people began building mud ridges along rivers as seawalls, called levees.

Researchers have found that floods have occurred 10 times more frequently in the last 1000 years compared to before the beginning of ancient Chinese civilization. Their analysis suggests that human activity, primarily the use of artificial levees, caused about 80% of this increase in flood rates, with the rest attributed to natural changes in climate, Yu said. says.

Computational modeling of rivers shows that mud barriers along rivers can lead to greater accumulation of sediment at the river bed. It makes things easier, says Yu.

“This study highlights the need to examine the extent of human activity that affects flooding in the context of climate change. This is an important message we must receive today,” said University of Illinois at Urbana. says James Best of Champaign School.

Artificial levees are no longer used to contain the flooding of the Yellow River. Since the early 1980s, the Chinese government has introduced policies to protect wild riverside vegetation, which keeps the soil around rivers in a stable state, he said. This helps keep the soil from falling out and may be a better approach, he says.

But in many parts of the world, building mud barriers is still the preferred flood control strategy, so research suggests other countries should also move away from artificial levees, says Yu. said. “We can learn lessons from studying the history of rivers,” he says.