Jingwei Fills the Sea

The story

Long ago, the Yan Emperor had a young daughter who loved the sea. One day she took a little boat out onto the Eastern Sea to explore. A storm blew up, huge waves crashed over her boat, and she was swept away and never came home.

But her spirit did not disappear. It became a small bird with a speckled head, a white beak and red feet. The bird flew over the waves crying “Jingwei! Jingwei!”, and so that became her name.

Jingwei was angry with the sea for taking her life and for all the other people it might take. She made a vow: she would fill the sea so it could never hurt anyone again.

So every day, Jingwei flew to the Western Hills, picked up a pebble or a twig in her beak, carried it all the way to the sea and dropped it in. The waves laughed at her. The sea was enormous, and she was tiny. But Jingwei never gave up. People say she is still flying back and forth today.

Reclamation: filling the sea for real

Land reclamation means creating new dry land in places that were sea, river or marsh.

The important word is volume. Even a small patch of land needs a huge amount of material. Here’s why Jingwei’s plan is so hard, with made-up but sensible numbers:

• One pebble: about the size of a grape, around 10 cubic centimetres.
• One cubic metre: that’s 1,000,000 cubic centimetres, so about 100,000 pebbles.
• Jingwei’s speed: if she managed 100 trips a day, filling just one cubic metre would take her 1,000 days, nearly three years.

The oceans hold about 1.3 billion cubic kilometres of water. Jingwei would need far longer than the age of the universe.

People succeed where Jingwei can’t because of machines. Huge dredging ships suck sand from the seabed and spray it where it’s needed, moving thousands of cubic metres in a single day.

A trap worth knowing: new land isn’t automatically solid. Sand and mud squash down under their own weight for years afterwards. Kansai International Airport in Japan, built on an artificial island in the 1990s, has been slowly sinking ever since, by several metres, and engineers keep adjusting the buildings to cope.

Rivers: nature’s Jingwei

Rivers are the world’s champion land builders. Rain and frost break mountains into tiny grains of sand and silt. The river carries them downstream. When the river reaches the sea, it slows down, and slow water can’t carry much, so the grains settle on the bottom. Layer by layer, a fan-shaped area of new land called a delta grows out into the sea.

China’s Yellow River gets its name from the yellow silt it carries. Its delta has grown out into the sea by large amounts within living memory.

How much land have people built? More than you might expect:

• Singapore is roughly a quarter bigger than it was in the 1960s, thanks to reclamation.
• About a quarter of the Netherlands lies below sea level, protected by dykes and pumps.
• Hong Kong’s airport was built mostly on land made from the sea.

Rivers can also take land away. When people build dams upstream, the dams trap sand and silt behind them. Less silt reaches the coast, so waves can start eating the delta faster than the river can rebuild it. Engineers now sometimes release floods of sandy water from dams on purpose, giving the river a chance to feed its delta again. Land at the coast is a balance between what the river brings and what the sea takes.

There’s a catch, and it would matter to Jingwei. Many coastal mudflats are vital feeding grounds for migrating birds, especially along the Yellow Sea. Filling them in can leave birds with nowhere to stop and rest. So engineers today have to ask not just “Can we build land here?” but “What lives here already?”

Let's try together

• Tray delta: fill one end of a baking tray with damp sand and tilt it slightly. Pour water slowly onto the sand. Where does the sand end up, and what shape does it make?
• Pebble maths: count how many pebbles or marbles fill a mug. How many mugs would fill your bath? Would Jingwei ever finish?

Question

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