“If children can do it themselves, they really learn it,” said Harcko Pama, a teacher at an elementary school in Heemstede.

“I know that they will remember this when they are older — it has such great impact,” he said.

Mr. Pama’s class of 11-year-olds competed in three separate teams to build the most flood-resistant castle. Armed with shovels and using hands and feet to tamp down the wet sand, the children improvised, some bringing seawater up to the castles in their shoes, others using towels to move the sand. Plots measuring about nine square yards were carefully lined along the shore. Organizers had timed the exercise so that the children (and the judges) could watch their work being destroyed by the incoming tide just after they had finished construction. Some 250 children competed.

As if part of the greater lesson, the children, from four different elementary schools in low-lying regions of the country, met on a stretch of beach less than 10 miles north of a major dike renovation project. The new dike protecting the seaside resort town of Katwijk will feature a reinforced concrete core and an underground parking garage. The project is to be finished early next year at a cost of nearly $70 million.

A recently released report by the Organization for Economic Cooperation and Development on water management in the Netherlands pointed to an “awareness gap” among Dutch citizens. The finding did much to get the sand castle contest off the ground.

But the awareness of the average citizen is only part of the problem. Many experts involved in technical aspects of water management warn of the rising average age of water professionals. Not only do fewer Dutch people worry about the rising tides, fewer go into technical fields, said Jaap Feil, who runs the National Water Traineeship program.