riffle

n (US) 1 (stretch of) choppy water in a stream, caused by a rocky shoal or shallow （礁石、 浅滩或浅水处的）急流, 湍流, 湍急流段. 2 shoal or shallow 浅滩; 浅水处.

ride, ride down, ride off, ride on, ride over, rider, ridge, ridge-pole, ridge-tile, ridgeway, ridicule, ridiculous, ridiculously, ridiculousness, riding, riding-crop, riding-school, rife, riff, riff-raff, riffraff, rifle, rifle-range, rifleman, rifling, rift, rift valley, rig, rig-out, rigging, right, right angle, right away, Right Honourable, right of way, Right Reverend, right-handed, right-minded, right-mindedness, righteous,