Alain, I'll attempt to answer your question, hoping that a better informed member will correct me if my answer is wrong.

The bridge rests on two bents, one on each side of the brook. Each bent has 11 vertical piles, to which various horizontal and diagonal wooden structural members are fastened.

But in addition, on each side of each bent--upstream and downstream--a pile called a batter pile is driven into the ground at a small angle away from vertical, so that the point where the batter pile enters the ground is a little further away from the vertical piles than the top of the batter pile is.

I think the angle from vertical is about the same as the legs of a man would have if he's standing with his feet about 1/4 to 1/3 of a meter apart. I believe the batter piles, especially the ones on the upstream side of the bridge, are intended to absorb the impact of ice or other objects flowing downstream, and thus protect the bents.

Those piles look very sturdy to me, so I think they will do the job.