The Collaborative International Dictionary of English v.0.48:

Alluvial \Al*lu"vi*al\, n.
   Alluvial soil; specif., in Australia, gold-bearing alluvial
   soil.
   [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Alluvial \Al*lu"vi*al\, a. [Cf. F. alluvial. See Alluvion.]
   Pertaining to, contained in, or composed of, alluvium;
   relating to the deposits made by flowing water; washed away
   from one place and deposited in another; as, alluvial soil,
   mud, accumulations, deposits.
   [1913 Webster]

WordNet (r) 3.0 (2006):

alluvial
    adj 1: of or relating to alluvium