Rivers usually flow into the sea and waves rise along the coast. What if a river suddenly goes against its nature and flows backwards with giant waves rushing upstream? Well, this actually happens and is known as a ‘tidal bore’.
What is a Tidal Bore?
A tidal bore occurs when tides coming from the sea push into a river or a narrow bay, reversing the river’s usual flow. However, a tidal bore can be caused only in certain conditions:
- The river should be shallow and the mouth should be narrow.
- The bay must be funnel-shaped.
- The region should have a large tidal range of at least six meters.
When these conditions are matched, the tide’s energy gets concentrated, causing the waves to move fast and sweep inland.
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The ‘Silver Dragon’ of China
One such river that showcases this phenomenon is China’s Quintang River near Hangzhou. It is popularly known as the ‘Silver Dragon’. The waves can tower up to 30 feet and move at 40 km/h. The wave’s loud roar can be heard even before it arrives, and water levels stay high afterwards.
This happens during every full moon, but most dramatically during autumn. An ancient festival marks the event and draws nearly 1,70,000 people every year. Historical records suggest the oldest tide table, dating back to 1056 AD, was created for this river.
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Global Wonders and Dangers
Apart from China, tidal bores take place at several places. Brazil’s Amazon River experiences Pororoca between February and March. Similarly, France’s Seine, Canada’s Peticodiac, and Mexico’s Colorado River experience similar phenomena. However beautiful they can be, they are very dangerous for sea travellers. Fatal accidents and damage to ships are a common story.
