Douglas Harper's Etymology Dictionary
Usage examples of "flood-plain".
In the spring, one of our guides assured us with unwonted cheer, it would overflow its banks, depositing nourishing silt on the flood-plains, hailed by the Akkadians as a life-giver.
The thick dark alluvial soil of the flood-plain gave way to light, gritty, brick-red stuff that supported a skimpy population of gnarled and thorny plants.