Balgstuw; it sounds Dutch, it’s cost effective Dutch and it protects in Dutch-style
Try to pronounce this in English: “Balgstuw”. Yes, it is Dutch, even more difficult than “Scheveningen” and it sounds something like ~bal-chchch-stew~ But what ís a Balgstuw? In short and way to simple; a Balgstuw is an inflatable, permanent-placed submerged dam, made of thick rubber curtains connected to a concrete structure at the bottom of a river, estuary, canal, waterway entrance or alike. Yes, the Balgstuw is an emergency flood barrier for serious water crossings, but much more cost effective than ingenious above-surface structures the Dutch are also known about.
Only at really frightening rising water levels, the Balgstew comes in action. In most of the cases fully automatic(!), and with concern of vessels that might be around. With a mixture of pumped-in surrounding water and air, the rubber mega-tubes rise meters above water level and protects the hinterland from the greater and pushing sea, lake or main river. To incidentally shut off an ocean bay for instance, the Balgstuw might not appropriate, but water areas to cross, and close, of 225 meters width (738 feet) are no exception for the developers of this ‘sleeping’ weir. More information and a video of a Balgstuw in rare action, you’ll find here