from The Century Dictionary.
- In French law, capable of floating boats or rafts: said of a watercourse.
Sorry, no etymologies found.
You cannot miss your way, of course, when travelling by river, but you can be at a considerable loss to know how far you have come since your last stopping-place, or rather you would be if the French government had not placed little white kilometre stones all along the banks of the "_navigable_" and "_flottable_" rivers, as they have along the great national roads on land.
The Oise is classed as _flottable_ from Beautor to Chauny, a distance of twenty kilometres, and _navigable_ from Chauny to the Seine.