Firstly: By whom was Dulauloy considered 'unreliable'? Presumably not by Napoleon since he had a high rank in the Guard. There does not seem to have been any proper inquiry as to how the bridge was blown up prematurely, much of what has been said is speculation.
Macdonald, "An attempt was made to lay at the door of a superior engineer officer the responsibility for this act and the neglect of preparations for crossing, but no-one dared to take steps to bring him before a court-martial; for it was quite clear that he had received no orders, and that on the contrary he had suggested to the Major-General the advisability of preparing points from which to cross, and that the answer given him had been that it would be time enough when the Emperor ordered it."
Macdonald was repeating hearsay, of course, but he took a deep personal interest in the matter and it can be assumed that he made enquiries at a high level.
Secondly: the people who were present seemed to consider that the problem was the several river branches rather than any swampy areas and that a few footbridges would have been practical. Macdonald, "It would have been easy to find many places at which men of different arms and of different corps could have crossed, owing to the narrowness of the river."
I'm quoting from Macdonald because that's what I have in front of me but there are other accounts, for instance Major Dumonceau speaking of the Elster : ‘This was only a few yards wide, but extremely steep banked & torrential.’
(Antony Brett-James , Europe against Napoleon, the Leipzig Campaign. 1970)