The Oosterschelde storm surge barrier
The storm surge barrier, which eventually cost 2.5 billion euros, was officially opened by Queen Beatrix on October 4th 1986. What had all this money been spent on? The chance to have another flood had decreased from once per ???? years to once per 4,000 years. Moreover, the storm surge barrier would not have to be replaced in the next two hundred years. Hopefully, one does not have to think about a new solution until the middle of the 21st century.