Rapid

A rapid is a section of a river where the river bed has a relatively steep gradient causing an increase in water velocity and turbulence. A rapid is a hydrological feature between a run (a smoothly flowing part of a stream) and a cascade. A rapid is characterised by the river becoming shallower and having some rocks exposed above the flow surface. As flowing water splashes over and around the rocks, air bubbles become mixed in with it and portions of the surface acquire a white colour, forming what is called "whitewater". Rapids occur where the bed material is highly resistant to the erosive power of the stream in comparison with the bed downstream of the rapids. Very young streams flowing across solid rock may be rapids for much of their length.

Famous quotes containing the word rapid:

“he dreadful darts
With rapid glide along the leaning line;
And, fixing in the wretch his cruel fangs”
—James Thomson (1700–1748)

“It now appears that the negro race is, more than any other, susceptible of rapid civilization. The emancipation is observed, in the islands, to have wrought for the negro a benefit as sudden as when a thermometer is brought out of the shade into the sun. It has given him eyes and ears.”
—Ralph Waldo Emerson (1803–1882)

“More rapid than eagles his coursers they came,
And he whistled, and shouted, and called them by name:
“Now, Dasher! now, Dancer! now, Prancer and Vixen!
On, Comet! on, Cupid! on, Donder and Blitzen!
To the top of the porch! to the top of the wall!
Now dash away! dash away! dash away all!””
—Clement Clarke Moore (1779–1863)