[vermaat]

The intesting part: The flood defense closes automatically at a water level of 3 meters above NAP (Amsterdam water level baseline) at Rotterdam or 2.9 meters above NAP at Dordrecht. The two doors, each 210 meters wide and 22 meters high, fill with water when the barrier closes. They then sink to the bottom in about two hours. A computer system automatically determines whether the barrier should be closed. However, a team from Rikswaterstaat is present to supervise.