As to whether it is better that the water should all be raised in a
single turn or in two?

The answer is that in one single turn the wheel could not support
all the water that it can raise in two turns, because at the half
turn of the wheel it would be raising 100 pounds and no more; and if
it had to raise the whole, 200 pounds in one turn, it could not
raise them unless the wheel were of double the diameter and if the
diameter were doubled, the time of its revolution would be doubled;
therefore it is better and a greater advantage in expense to make
such a wheel of half the size (?) the land which it would water and
would render the country fertile to supply food to the inhabitants,
and would make navigable canals for mercantile purposes.

The way in which the river in its flow should scour its own channel.

By the ninth of the third; the more rapid it is, the more it wears
away its channel; and, by the converse proposition, the slower the
water the more it deposits that which renders it turbid.

And let the sluice be movable like the one I arranged in Friuli
[Footnote 19: This passage reveals to us the fact that Leonardo had
visited the country of Friuli and that he had stayed there for some
time. Nothing whatever was known of this previously.], where when
one sluice was opened the water which passed through it dug out the
bottom. Therefore when the rivers are flooded, the sluices of the
mills ought to be opened in order that the whole course of the river
may pass through falls to each mill; there should be many in order
to give a greater impetus, and so all the river will be scoured. And
below the site of each of the two mills there may be one of the said
sluice falls; one of them may be placed below each mill.