I'm no expert on this, but could this be the reason of the confusion in the picture titled "Section of the Quai de Gare usine: 1892", where the author mentions

I'm no expert on this, but could this be the reason of the confusion in the picture titled "Section of the Quai de Gare usine: 1892", where the author mentions "A = drying channels (not sure what that means- they look like sewers in cross-section. May just mean 'drainage')"?