Factoid Fred Explains Locks
The circular device is for manually opening the lock gates and is called a capstan, I believe. The holes at the top are for storing the poles, which when in use go in the side holes, turning the device and opening the gates. The other shots are of the gates in use – water dropping into the lock below, to allow a barge to descend from one level to the next or conversely rise up to the next level. The other two shots show one side of the gates and the reinforced box design on the other.