DCHP-1 Online
flat rapid Northwest 
a fast-moving stretch of water over a relatively smooth bed. See 1954 quote at riffle (def. 1c).
See also: riffle ((n.)) (def. 1c)
- 1849 What I took for a ford at a distance was a "flat rapid" with a considerable depth of water running over a smooth bed of rock.
- 1849 What I took for a ford at a distance was a "flat rapid" with a considerable depth of water running over a smooth bed of rock.