The whitewater classification system groups rapids into six levels of difficulty ranging from basically ripples to huge waves and dangerous rocks and currents. Wikipedia has an excellent piece on the classification system with an explanation of the types of rapids to be found in each class. Good luck and...be careful!
georgieria
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Rapid means something which occurs quickly (fast), As in, "he flipped through the dictionary rapidly" Rapid also refers to a section of a river where the river bed has a relatively steep gradient causing an increase in water flow and turbulence.
usually a shallow part of a river with a fast current
The address of the West River History Conference is: Po Box 9276, Rapid City, SD 57709-9276
Due to the rapid water and uncertain depth of the river, I was not sure that I could ford the river.
This is known as a glissando.
canyon
A fast-flowing and turbulent part of the course of a river.
canyon