The term that describes low land that has been drained of water is "marsh" or "wetland." These areas can be artificially drained for agricultural purposes or to prevent flooding, turning them into more arable land. However, when drained, they may lose some of their ecological functions, such as water filtration and habitat for wildlife.
It is an area of land that is drained by a river. It is also a ridge or elevated area of land that divides two areas of land that are drained by two river systems.
watershed
watershed
A river
A catchment.
Land drained by a river is a watershed. This is an area of land that feeds all the water running under it and draining off of it into a body of water.
river
I believe you might be referring to a "watershed".
watershed
jjj
Drained lands are lands which used to be swamps, but which had a lot of water removed in order to make them into more usual dry land that can be used for farming, housing etc.
they get big long pipes and walk to the sea so they can join the pipes and make a water sucking tunnel.