Nature controlled demolition.
I think there was a real problem with the design of linear bracing. :too much focus on allowing the flood waters to flow without much to hinder its pass.

I have seen a bridge over the Nyrang river demolished by a tree in flood waters: it was travelling downstream across the river.

The first Queen st bridge (brisbane) suffered the same fate when a barge was pushed against it during a flood in about 1893. My mum's great aunt told me the story & many others. She saw three bridges in the same spot.