I think its the meandering of a stream. Maybe the water is quite deep in a ravine its carved there, or maybe its a stream that doesn't always flow.

Trenches. Beaumont-Hamel was part of the Battle of the Somme. Beaumont-Hamel was also the place where a large amount of Newfoundlanders, people from the island of Newfoundland (where I'm from), died. 780 men went into that battle. The next morning, 68 were available for role call.