Tides and Rivers Combine to Make Floods Worse

Topic: Earth Science

Scientists studied two big floods in China's Yangtze River. They found that tides can make river flooding worse by adding more water. This happens when the tide is high and the river is not at its peak flow.

Ocean tides push upstream along coastal rivers, reaching hundreds of kilometers inland. These areas are called tidal rivers, where the river current meets the tidal oscillations. When rivers flood, tidal dynamics can add to the river's height, increasing overall peak water levels and making flooding worse.

In China's Yangtze River, two big floods happened in 1954 and 2020. The researchers combined data on river discharge and tides from both floods with a tidal model to study how the interactions between the river and incoming tides created high water levels. They found that peak water levels occurred around one to two weeks after peak river discharge during perigean spring tides, when the sun and moon are in the right positions for high tides.

The researchers also discovered that peak river discharge rates can suppress subharmonic tidal amplitudes, while intermediate rates allow for greater amplitudes and higher water levels. Additionally, it takes time for river water to move downstream, so water levels are higher after floods, adding to the effects of tidal inflows.

Why It Matters

Floods in India can be made worse by tides, just like in China's Yangtze River. Understanding this can help us prepare and prevent damage from flooding.

Key Facts

• Two big floods happened in China's Yangtze River in 1954 and 2020.
• Tides can make river flooding worse by adding more water.
• Peak water levels occurred around one to two weeks after peak river discharge during perigean spring tides.
• More than 3,380 kilometers of tidal rivers are potentially exposed to floods caused by similar mechanisms.
• The Three Gorges Dam helped create higher water levels in 2020 by deepening the channel.

Key Terms

Perigean Spring Tides

High tides that happen when the sun and moon are in the right positions.

Implications

Floods in India can be made worse by tides, just like in China's Yangtze River. Understanding this can help us prepare and prevent damage from flooding.