Gemaalcomplex Buma...

at the left the Lemster "schut"lock  and at the right the water pumping station Buma...
at the left of this is Friesland and the lock and water pumpingstation is Flevoland... 

In this type of locks, the door was closed until the water level had risen so far that all ships were in. Then the door was opened and one could go to the next canal house. There was not always enough water to get all ships per passage until the next one. One had to wait again until there was enough water. 
Another use was that in the area with waters that were under the influence of ebb and flow. Here man only could pass when the water was in the same level...