Medieval Northern France

Just about all monastic orders were operative in France, but which ones would have been found in the valley of the Somme would be specialized knowledge and you would need an expert on the church and monastic orders. The Somme flows into la Manche (the sleeve) as the French have called it for centuries--the English call it the English Channel (surprise, surprise). It flows through a syncline, a geological term for what we might call a trough. It is a slow river, and does not drain a very large area, so the river levels are pretty stable. The lower river is somewhat affected by tides, but not much--at Blanchetaque, where it enters the sea, there are extensive marshes which take up most of the excess water at high tide. Blanchetaque is the last point at which the river can be forded before the sea, and the difference between low tide and high is only about three or four feet. As the Somme does not drain a great deal of land, it is not subject to any noteworthy flooding.

Do I smell a really crappy novel in gestation?

I had similar thoughts, but refrained from comment.