Much is often said about the trench systems of the western front in WW1, and they are often described with wordage that indicates a single, unbroken line of trenches stretching without interruption from the Swiss border to the English channel.

But how contiguous were these trench systems actually? Could a soldier in actuality walk all of the way without leaving the trench system? This question excludes of course the considerable hinderances and dangers of offensives, sporadic artillery bombardment, sniper fire. As it is quite difficult to dig trenches across rivers, these are also excluded from this theoretical.

I am aware that the trench system was also often in flux due to capturing and recapturing of trenches by both sides. Did this create broken trench lines? And were there other obstacles of the natural variety besides rivers that hindered a fully conjoined trench system from forming?