Reclaiming the Zuiderzee: How the Dutch Turned Sea into Land

A For centuries the Zuiderzee, a broad and shallow arm of the North Sea reaching deep into the heart of the Netherlands, was both a blessing and a curse to the people who lived around it. Its waters carried trade and teemed with fish, yet they were also a standing menace. Whenever a north-westerly gale drove the sea inland, the level of the Zuiderzee could rise with terrifying speed, and the low-lying farms and villages along its shores were repeatedly flooded. Dykes were built and rebuilt, but the threat never went away, and generations of Dutch families lived with the knowledge that the water they depended upon might at any moment turn against them and sweep their land away.

B The idea of taming the Zuiderzee once and for all, by sealing it off from the sea entirely, had been discussed for generations, but for a long time it seemed little more than a dream. Its most determined champion was an engineer named Cornelis Lely, who worked out a detailed scheme for enclosing the inland sea with a great barrier and turning much of it into farmland. For many years, however, the plan was dismissed as impossibly expensive and technically reckless, and successive governments were unwilling to commit the enormous sums it would demand. Lely pressed his case for decades, refining his calculations and waiting patiently for the political mood to change.

C Two events finally tipped the balance. In 1916 a violent storm broke through the coastal defences and flooded a wide stretch of land around the Zuiderzee, drowning livestock and destroying homes and reminding the nation, in the most brutal way, of its vulnerability. At almost the same time the First World War, though the Netherlands remained neutral, cut off many food imports and made the country anxious about feeding itself. Suddenly the prospect of creating a vast area of new agricultural land looked less like an extravagance and more like a necessity, and within a few years the government committed itself to the great project.

D The heart of the scheme was a mighty barrier dam thrown across the mouth of the Zuiderzee, sealing it off from the open sea. Building it was a colossal undertaking. Working from both ends towards the middle, engineers gradually narrowed the gap through which the tides rushed twice a day, until only a fierce, fast-flowing channel remained. The dam was built up mainly from boulder clay, a stiff glacial material dredged from the seabed, which packed together to form a watertight core resistant to the pounding of the waves. When the final gap was at last closed, the tides were shut out and a long chapter of the region's history came to an end.

E Cut off from the salt tides, the enclosed water slowly turned fresh as the rivers that fed it flushed out the sea salt, becoming a great inland lake. Behind the dam, engineers then set about the second and even more ambitious half of the plan: draining large sections of the lake bed to create new land. Ringed by dykes and emptied by powerful pumps, these reclaimed areas, known as polders, emerged from beneath the water as level expanses of rich, dark soil. In time they were drained, drained again, planted and settled, and eventually an entirely new province, complete with farms, roads and towns, was laid out on ground that had recently lain beneath the waves.

F The transformation was not welcomed by everyone, and it carried real costs alongside its triumphs. The old Zuiderzee had supported a thriving fishing industry, and the fishing communities that ringed its shores saw their livelihoods vanish almost overnight when the salt water and the fish that lived in it were shut out for good. Ancient ports found themselves stranded miles from any open sea, their harbours useless. Yet the wider benefits were undeniable: the land behind the dam was now safe from the sea, a huge area of fertile farmland had been won, and the freshwater lake became a valuable reserve of drinking water. The draining of the Zuiderzee remains one of the boldest feats of engineering ever attempted, a reshaping of the map so complete that the sea itself was made to retreat.