Dutch Vigilant as Old Enemy Threatens : Disaster: Forty years after the sea breached dikes and killed nearly 2,000 people, experts warn that the tragedy could repeat itself.

OUDE TONGE, Netherlands — Forty years after killer floods spawned a high-tech defense against the sea, man and the elements are still the essence of the battle.

Two long rows of graves on the harbor dike in this farming town remind villagers of the constant threat of the North Sea. As more than half of the 15 million people in the Netherlands, they live below sea level.

“Just about every village around here has a mass grave like this one,” said Jannie Nijssen, a potato merchant who was 13 when waves washed over the embankments before dawn on Feb. 1, 1953.

It was the Great Flood, a combination of spring tide and hurricane-force winds that breached the dikes and killed 1,835 people.

Despite the ambitious Delta project of dikes and dams the disaster inspired, experts say it could happen again.

Holland’s chief sentry against a recurrence is Jan Kroos, head of the Storm Signal Warning Service in The Hague. He is a hydraulic engineer who tracks weather and tide levels at 100 coastal points and sends alerts whenever the sea is expected to surge more than 3 feet above normal.

Kroos worries that people with short memories will underestimate the danger.

“You have to be prepared for the possibility that no one will believe you when it really happens,” he said. “It can get a lot worse than it was in 1953.”

The Dutch have always fought the sea, and in the process have reclaimed thousands of square miles of land. But not since a series of floods in the Middle Ages had they experienced anything like the catastrophe of 1953.

As the nation slept, dikes gave way at more than 400 points. Swirling seas covered hundreds of square miles, submerging farms and villages.

Floods forced the evacuation of 72,000 people and damaged 47,000 buildings. For weeks, up to 6 feet of water covered the provinces of Zeeland and South Holland.

The high death toll was blamed on the central government’s failure to heed warnings from the coastal villages.

“I told them how high the water was, that we still had several hours to go before high tide and that I was afraid the dikes would give,” said Cor van der Hooft, then-mayor of Willemstad on the Hollands Diep inlet.

In a new book, “The Disaster: A Reconstruction,” Van der Hooft is quoted as saying that his boss, the provincial commissioner, went back to sleep when reassured by national authorities that the mayor must be exaggerating.

Because Van der Hooft sent parties to wake the people of Willemstad and reinforce the dikes, only two people were killed in the town.

Oude Tonge, 10 miles away, was less fortunate. Its mayor was awakened at 3 a.m. by a brick flung through his window as water coursed through the streets. More than 300 of the 4,000 townspeople drowned.

After the flood, Parliament passed the Delta Act to create an 800-mile bulwark of new or heightened dikes and gates along Holland’s shoreline.

Its most ambitious segment is a storm-surge barrier across the mouth of the Eastern Scheldt inlet, with dozens of huge gates designed to blunt the force of the sea. The last phase of the Delta project is a gate to seal off Rotterdam port, the world’s largest.

The Dutch are ever wary of their old enemy, and Kroos is not the only one who fears that the new dike system will create a false sense of security.

Karel Leeftink of the Delta dike-engineering museum warned against being “lulled into sleep,” as the country was the last time.