Floodplain
"Land area adjacent to a river or stream that can be covered by water when a river or stream over ows its banks. The extent of the ood plain depends on topography and the magnitude of a given ood event." (Virginia Polytechnic Institute and State University, n.y.)
Sources
Virginia Polytechnic Institute and State University. "A Glossary of Water-Related Terms", by Brian Benham. Publication 442-760