This is a brief description of the functioning of locks and dams. In combination, a lock and dam 1) raise the level of a river allowing the safe passage of boats and 2) allow boats to pass from the low to high or high to low sides of the dam.
Lock #10 had to raise and lower the water level by approximately 6 feet on the day we took these photographs. You can see the water level. The lock has two valves that allow water to enter from the high side and exit from the low side. Opening one or the other raises or lowers a boat within the lock.
Barges are lashed together and pushed by a tug. In the case of Lock #10, the flotilla was too long to pass through the lock without being broken into two sections. The individual barges are lashed together and those work work to move them must take the flotilla apart and then put it back together to get the through some locks.
Once separated, the forward collection of barges floats out of the lock because of the movement of the water. This section is tied up close to the lock so the entire flotilla can be put back together quickly.