riffle ((n.)) † [origin obscure; cf. ruffle, ripple]
1a n. an obstruction in a watercourse, as a shallows, rapids, or sandbar.
See also: ripple (def. 1) shoot ((n.)) (def. 1) rift
1b n. a stretch of ruffled water caused by such an obstruction; the place where such an obstruction is.
See also: ripple (def. 2) rip ((n.))
1c n. Northwest a fast-moving stretch of water over a relatively smooth bed. See 1955 quote.
See also: chute (def. 2) dalle (def. 2) flat rapid run ((n.)) (def. 1) slide (def. 1b)
2 n. Placer Mining the transverse barriers placed across the bottom of a sluice-box to arrest the particles of gold.