Rivers, eddies, and the Naviglio canal
Studies of river currents and bank erosion with a Mediterranean map and canal dimensions
Under the repeated heading 'Of rivers', Leonardo works out how the shape of a channel governs the water's speed and how uneven currents carve unequal depths, throw up gravel, and spin eddies that gnaw and shift the banks. A canal is drawn crossing over a river, and a note reckons the Naviglio's dimensions, worth and yearly return along with the size of the largest boats and how a narrow trench is first dug to find the true water level. A red outline of the western Mediterranean coast and a fragmentary column beside a moon-and-sea sketch complete the sheet.
On this page
A river that keeps its banks
Of rivers. The river that has a continuous lowness in the middle of its course will maintain its banks, keeping the fast water to the centre away from the sides.
Narrows speed and scour the water
Where the canal is narrower the water runs more strongly than elsewhere, and on leaving the narrows it spreads with fury, striking and consuming the neighbouring cross-banks, often changing its course from one place to another.
Coast of the western Mediterranean
A red-drawn stretch of the western Mediterranean coast is lettered a, b m, c n x, d o, e, with the sea itself marked as the Mediterranean.
The Naviglio canal and its boats
The largest boats are 7 1/2 braccia wide, 42 long and 1 1/2 high at the sides. The Naviglio, worth 50 gold ducats, yields 125 thousand ducats a year, is 40 miles long and 20 braccia wide; at the start a narrow trench is dug to find the true water level and then widened.
Why an uneven course cuts uneven depth
A river of unequal course makes unequal depth and width, because the faster part descends from a more sloping bed, then strikes where the slope ends, lifts the gravel and heaps it into a resisting bank; the water flattens between course and bank, and the oncoming surface strikes upon the still water.
The making of eddies
A disordered course in the middle of the river makes two contrary eddies that gnaw the banks they strike. Nearer one bank it deepens that side, hollows under the bank until it collapses, then turns its impetus to make a single eddy as great as the first two.