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Monday, 4 August 2008

Pororaca: Bore surfing the longest wave

There are a number of surfable tidal bore waves in the world and we have mentioned a few in the past on this blog and they never fail to amaze. This is the latest footage from a surf trip to surf the Pororoca bore on the Amazon, one of the longest waves in the world and judging by this session one of the biggest and cleanest. On the video below these guys really scored. For the science of tidal bores check out the explanation below:

Tidal bores form on rivers and estuaries near a coast where there is a large tidal range and the incoming tide is confined to a narrow channel. They consist of a surge of water moving swiftly upstream headed by a wave or series of waves.

When a tidal bore forms in a river, the direction of flow of the water changes abruptly as the bore passes. Before it arrives, the water may be still or, more usually, a small freshwater current flows outward toward the sea. The tide comes in as a “wall of water” that passes up the river. Behind the bore, the current flows upriver. At the division between the moving water behind the bore and the still water in front, there is a wave, the water surface behind being higher than it is in front. This wave must travel more quickly than the water particles behind it, because, as the advancing water travels upriver, it collects the still water in front and sets it in motion. Upriver, the advancing tide will consist not of salt water from the sea but rather of fresh water that has passed farther down and been collected and returned in front of the incoming tide. It is therefore necessary to distinguish between the velocity of the advancing wave and that of the water particles just behind it.

* source of the Encyclopedia Brittanica.

1 comment:

Anonymous said...

Awesome and amazing!!!

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