How a straight channel scours its own bed
Red-chalk sections of a flat and a curved channel bottom
A small red-chalk drawing at the top shows two channels seen in section, one with a flat bed and one curved. The notes reason that a straight channel of even depth and slope soon hollows out more in the middle than near the banks, because the water there runs faster and, at equal height, lifts and carries more. A further note adds that water which has been constricted breaks both bank and bed after its fall.
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The middle of a straight channel wears fastest
A straight channel of equal depth and slope will in a short time hollow out more in the middle than near the bank, for in the middle of straight channels the water runs faster than at the sides, and where the water moves more, being of equal height, it lifts and erodes more.
Constricted water breaks bank and bed
Water that has been pinched or narrowed will break the bank and the bottom after its fall. The pent-up stream, released, tears at the channel where it drops.