The flooded areas are among the flattest parts of England. When the hills are worn down we may get flat plains again, but there are quite enough hills left in England to prevent this happening for a very long time. In the last million years this process was interrupted by the Ice Age, or more accurately a succession of four Ice Ages. Ice does not necessarily move downward, like water. On the contrary, it can be pushed some way up hill by pressure from behind. It can also carry much more solids than water, including even large rocks. The flooded areas in the fens and in Yorkshire have all been lake beds at one time or another during the Ice Ages. During the middle ages monasteries were built on islands in fens, such as Ely and Crowland, and the monks did a bit of drainage. The biggest drainage schemes were carried out in seventeenth century when bourgeoisie was gaining power.