The Collaborative International Dictionary of English v.0.48:

Sedimentation \Sed`i*men*ta"tion\, n.
   The act of depositing a sediment; specifically (Geol.), the
   deposition of the material of which sedimentary rocks are
   formed.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sedimentation
    n 1: the phenomenon of sediment or gravel accumulating [syn:
         deposit, sedimentation, alluviation]