A riffle is the little brother of a rapid. It is a shallow section of stream where sediment has been deposited, often in response to the upstream scouring of a pool. As water flows over the obstruction, the current becomes more turbulent and breaks into a succession of small waves. Riffles produce some of the happiest voices of a river, murmuring and chattering, never roaring or growling with argument.

William deBuys