Canal to Florence: gravel banks and an aqueduct bridge
Palisades against gravel erosion; a three-arched bridge for floods; digging cost and season
Three linked studies for the Florence canal. The top note, labelled 'gravel' (ghiara), warns that on gravelly banks the moving water gnaws away the sand that binds the gravel, so the channel collapses; the remedy is 3 or 4 braccia of level ground between bank and water plus a plank palisade between the piles and the gravel. A middle drawing shows the canal carried over a river on a bridge, urging three arches instead of one because of floods. The lower drawing, lettered a–e–o with M and N, gives the profile of the canal bed and estimates the cost of digging and the best season for the work.
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Protecting gravelly canal banks (ghiara)
Where the banks are gravelly, keep the enclosed water from touching them, for the current gnaws and carries off the sand that binds the gravel, and the bank collapses and fills the channel. Leave 3 or 4 braccia of level ground, rising a braccio above the water, and set a plank palisade between the piles and the gravel.
Three-arched bridge for the canal over a river
If the river ordinarily fills the width of one arch, make the bridge have three, on account of the floods.
Canal-bed profile, cost and working season (a e o, M N)
The bed a e o should begin very low at o and finish as high as possible at a, near the common ground level, so the bridge arches sit high above the flooding river. Digging costs no less than 4 dinari the braccio at 4 soldi a day per worker, and the work should run from mid-March to mid-June when peasants are idle, cheap, and the long days do not tire them.