Yes, ALLUVIONS is a Scrabble word!

Letter values in Scrabble US: A 1, L 1, L 1, U 1, V 4, I 1, O 1, N 1, S 1.

Is it a valid word?

ALLUVIONS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

gradual formation of new land, by recession of the sea or deposit of sediment
the rising of a body of water and its overflowing onto normally dry land
clay or silt or gravel carried by rushing streams and deposited where the stream slows down

Also: alluvial sediment, alluvial deposit.