Colliding Currents Fight and Ruin the Banks
Red-chalk notes on erosion and the mingling of currents
A red-chalk leaf on colliding currents, with sketches of a current striking back and of the water's rotary motion. Leonardo writes that water moving against motionless water fights and ruins its own banks, an observation on erosion where flows meet. He adds that water carrying the greater motion penetrates and passes through the lesser motion of other water, just as moving air passes through still air.
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Moving water fights and ruins the still water's banks
That water which moves against motionless water fights and ruins its banks. The note captures how erosion concentrates where a live current meets standing water.
Faster water penetrates slower water, like air
Water with its greater motion penetrates and passes through the lesser motion of the other water, in the likeness of the air. The proposition is numbered 21 among Leonardo's water studies.