River Eddies, Floating Debris, and Scour Beneath a Gate
Where gravel and sand settle, and how a sluice-gate hollows the riverbed
Three short river notes with two marginal sketches: an eddy above and, below, water plunging beneath a gate into a swirl. Leonardo maps where gravel (ghiara) and sand (rena) settle between the current and a back-eddy, with light timber and other buoyant things trapped inside the eddy itself. He adds that in still air a floating object travels more slowly at the surface than just below it, and that water issuing over a level bed under a sluice-gate scours the bed both before and behind the gate.
On this page
How gravel, sand and floating timber sort themselves at an eddy
Between the current and the back-eddy (retroso) lies the sand (rena); between the sand and the eddy lies a clean hollow, whence the eddy turns; and within the eddy itself lie timber and other light things. The margin note labels gravel (ghiara) and sand (rena).
A floating object is slower at the surface than just beneath it
If the air is still, a thing carried by the water's current at its surface moves more slowly than one carried just below that surface. Leonardo isolates the effect of the still air on the exposed part of the drifting object.
A sluice-gate scours the level bed before and behind it
Where water issues over a level bed beneath a sluice-gate, it hollows out the bed both in front of and behind the gate. The lower sketch shows the plunging jet and the swirl it excavates downstream.