I believe you might be referring to a "watershed".
watershed
watershed
A catchment.
Basin
a watershed, also called a drainage basin, is an area drained by a river.
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.
watershed
jjj
The area of land drained by a river is called a "catchment area". It is so-called because is the the area that catches the precipitation (rainfall).Another term is "river basin", but this is less specific.(The geographical term, "catchment area", is often used to describe the area served by, say, a school or hospital).
basin
Because it is the land area that supplies water to a river system :)
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.