Question

why the bridges are built inclined to the perpendicular of a canal​

Answer 1

Answer:Because:

a) you want the most economic bridge (already said in other answers) and

b) you look for a straight section of the river because it is more stable (not mentioned)

If you build on a bend or a curve of the river, the river will move over time and erode the accesses and you want the water to pass under the bridge, not to wash the bridge away.

The only exception is where you are unable to find solid rock to anchor the bridge abutments.

Explanation:

Answer 2

Answer:

Probably 99% of the bridges are built perpendicular to the waterway. As others have said building bridges is expensive and straight across ..