Why does a truck with a fixed chassis rail at that height not have front-underrun protection below it? This is a serious design flaw.

No, it would be pronounced the same as bureau, but spelled differently.

Beuro works as a pun for English, French and German

A quick Google shows that the maximum draught advertised on that canal is 1.32m, so that(plus whatever safety margin canals offer in their design) is presumably the minimum depth at any point of the canal. It would likely have areas which are somewhat deeper.

It also consists of a series of locks which increase elevation by approximately 2.5m each, so any one of those if full would be too deep to stand up in.