Geograph - photograph every grid square

In a staircase the upper gate of one lock is also the lower gate of the one above it. Operating a staircase is very different from operating a flight. It can be more useful to think of a staircase as a single lock with intermediate levels. As there is no intermediate pound, a chamber can only be filled by emptying the one above, or emptied by filling the one below; thus the whole staircase has to be full of water (except for the bottom chamber) before a boat starts to ascend, or empty (except for the top chamber) before a boat starts to descend. In an apparent staircase the chambers still have common gates, but the water does not pass directly from one chamber to the next, going instead via side ponds. This means it is not necessary to ensure that the flight is full or empty before starting. Examples of real staircases are Bingley and Grindley Brook. Examples of apparent staircase locks are Foxton Locks and Watford Locks on the Leicester Branch of the Grand Union.