After North Sea flood in 1953 a $650 million plan was made damming up four of the region’s principal sea arms. Fortnight ago the Delta Plan marked its first milestone.

On one calamitous day early in 1953, a howling northwester teamed with a wild spring tide. The resulting floods were the most disastrous to afflict The Netherlands in five centuries. Hardest hit were 1,300 square miles of Rhine and Meuse delta lands in The Netherlands’ southwest, where tidal surges roared…