Water Around a River Rock: Sand Deposits and Whirlpools
How a rock that divides a current lays down sand or, when submerged, spins the water into eddies
Two small pen sketches show a rock (scoglio) in a river with the current dividing and rejoining around it, and the text explains the resulting flow. Where a rock rises above the water and splits the current, the calm interval between the rock and the point where the water rejoins becomes the place where sand settles. Where the rock is submerged, the water pours over it, scours its foot, and turns in whirling eddies because the rejoining streams cannot at once run on. A third heading labels a diagram of such a 'whirlpool' in the river bed.
On this page
Sand settles behind a rock that splits the current
If the reef 'a' of the river rises above and divides the course of the water, which afterward rejoins itself, then the interval that lies between the reef and the rejoining of the water is where sand will be deposited. The upper sketch shows the divided current closing again downstream of the rock.
A submerged rock scours its foot and spins the water
If the rock that divides the current is covered by the running water, the water passing over it falls behind it, scours at its foot, and makes it turn; the water plunging into that hollow rotates in whirling eddies above and below. This happens because the two streams, already divided by the rock, cannot at once run on their way when they rejoin.