How a weir's fall shapes a river's windings
Channel a b fills with sand as the river re-swells
A drawing of a winding river channel with a weir (pescaia) accompanies a note on how the fall of water shapes a river's course. Leonardo writes that water falling with great force from its weir gives the rivers their windings along the line of that fall; but when the water lowers, even where the line a b once held, the channel a b will fill with sand as the river swells again, so the main body of water follows its natural course. The sketch marks points p and v and the channel labelled c d - a - b, with a hatched weir at the foot.
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Weir and the winding of a river
The water falling with great force from its weir gives the river its windings according to the line of that fall. When the waters lower, even though the line a b had held its place, as the river swells again the channel a b fills with sand and the mass of the water follows its natural course. The drawing marks the channel c d - a - b.