Surge

Like the underwater breath of a dragon, the surface of the river suddenly wells up in an unpredictable wave. But it isn’t a dragon. A surge is created when water flows over an obstacle, such as a boulder, submerged deep in the water, causing the water above it to swirl. Also known as boils, surges are rarely powerful enough to tip a raft, but they can spin it and twist it off its course.


 
 
Anatomy of a Rapid

 
 
 
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