When fully open the barrier provides a 360 metres wide passage to the ships. On a storm surge warning of more than 3 meters, the barrier is closed automatically through fully computerised operations. The huge gates float on water and on closure are filled with water so that these sink to bottom to provide adequate safety against storm surges.
Image from Flickr is by Nils van der Burg
Image from Panoramio is by Bob Fleumer
A 1:250 scale working version of the barrier at Madurodam miniature village.
Image from Flickr is Marco Vossen
Image from Flickr is by LearningTour
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Source of info: Wikipedia
More info at the official web site: www.keringhuis.nl