Watercourse: Depth Traded for Width and for Speed
A wider or faster channel runs shallower
Two paired notes on the shape of a watercourse, with a red-chalk channel profile sketched on the lower half of the sheet. Over a bed of equal slope, Leonardo reasons, the water is shallower where the channel is wider. Between banks of equal width, likewise, the water is shallower where its course is swifter. The two rules together relate a stream's depth to its width and its speed.
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Greater width means less depth
Water running over a bed of equal slope will have less depth where it is of greater width.
Swifter course means less depth
Water running between banks of equal width will have less depth where it possesses the swifter course.