Riffle

Riffle is a term used in fluvial geomorphology to describe a shallow, fast-moving section of a stream or river where water flows over a relatively coarse bed. The rapid flow and surface turbulence produce mixing and oxygenation and often expose gravelly substrates. Riffles typically alternate with deeper pools, forming riffle-pool sequences that contribute to habitat diversity. Their size and occurrence depend on flow regime, channel slope, and sediment supply, and they are common in natural rivers as well as in restoration projects.

In card games, a riffle shuffle is a common method of mixing a deck by splitting it into two halves and releasing them so the cards interleave. The action, sometimes described as a cascade, is widely used in casual play and magic performances. Variations include the faro riffle and multiple riffle sequences.

As a verb, to riffle means to move quickly through something, turning pages or examining papers rapidly. Phrasal usage includes riffle through a book, a file folder, or a pile.

Riffle is sometimes confused with rifle, the term for a long-barreled firearm; the two are distinct despite similar spelling.