alluvial flat vs alluvial plain

alluvial flat and alluvial plain both are nouns.

Word	Noun	Adjective	Verb	Adverb
alluvial flat	Yes	No	No	No
alluvial plain	Yes	No	No	No

As nouns, alluvial flat and alluvial plain are synonyms defined as:

alluvial flat and alluvial plain: a flat resulting from repeated deposits of alluvial material by running water

alluvial flat (noun)	alluvial plain (noun)
a flat resulting from repeated deposits of alluvial material by running water	a flat resulting from repeated deposits of alluvial material by running water