Reflected waves colliding in mid-channel of a river
Water higher and deeper at mid-width, and the meeting of waves rebounding from the banks
Leonardo observes that in a straight-banked river the water stands higher, and the bed lies deeper, at the middle of the channel than at the sides. He then treats waves that rebound from the banks: reflected waves meet in mid-channel and, if of equal force, leap back equally. If the reflected wave is stronger than the one it meets, the higher rides over the lower and passes along an incident line to the opposite bank. Small hatched and crossing diagrams labelled a, c, d, b accompany the argument.
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Profile of a straight-banked river
The waters filling the banks of straight rivers are always higher at the middle of their width than at the sides, and the bed of such a river is correspondingly deeper at mid-width than toward its edges. This sets the profile within which the wave motions are analysed.
Equal reflected waves rebounding at mid-river
Waves reflected from the impact they first made on the bank meet in the middle of the river. If they are of equal force they leap back equally. The lettered figure a, c, d, b at the right illustrates the symmetrical meeting.
A stronger wave riding over the weaker
If the reflected wave is more powerful than the one it meets in mid-channel, the higher wave rides over the lower and passes along an incident line to the opposite bank. The crossing lines at the lower right sketch this oblique override.