The Special Operations Bureau was in action again last weekend, this time travelling to the Charente. Once again, along the way we found (purely by coincidence) a weird thing, but whereas the last one was an array, this weired thing was a river.
The barrage itself is pretty normal - a line of rocks cemented in place across the river, damming the river to provide a decent fall of water to power the mill, but along it are a series of structures which look like mini locks.
These are eel traps, and although we didn't stop to ask I assume they work for elvers swimming upstream to grow into adults, and the adults returning downstream to breed (which they do in the Sargasso Sea).
The locks are interesting compared to the UK equivalent. Whereas in the UK you need a lock key (or more properly a windlass) to operate the hidden mechanism of a lock, the lock mechanism here is a big wheel which you turn.
The method of opening the lock gates differs here too - most locks in the UK are opened by pushing the gates open, whereas here you use another wheel and a chain driven mechanism to wind the gates open.