How a Constricted River Rises and Erodes
Water in a narrowed parallel channel gains height as it loses width
The page states a principle of volume applied to flowing water: a long body of uniform thickness swells on two opposite sides by as much as it is lowered on the other two. Applied to a parallel-sided river that is constricted, the water rises in height by as much as it loses in width, so that on falling back it hollows out the place it strikes. Leonardo adds that such rivers can be narrowed in two ways, from surface to bottom or along their opposite sides; a small channel study is sketched below.
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A constricted river rises as it narrows
Where a parallel-sided river is constricted, the water gains as much in height as it loses in width, and in falling back it scours out the place it strikes. Such rivers may be narrowed in two ways: from the surface down to the bottom, or along their opposite sides.
A uniform body swells on two sides as it is lowered on the others
Leonardo states the underlying principle of constant volume: a long body of uniform thickness swells on its two opposite sides by exactly as much as it is lowered on its other two opposite sides. This rule of compensation governs the behaviour of the constricted water described below it.