noun (n)

• clay or silt or gravel carried by rushing streams and deposited where the stream slows down(noun.object)

  Synonym:
  alluvial deposit, alluvial sediment, alluvion
  

  source: wordnet30
• Deposits of earth, sand, gravel, and other transported matter, made by rivers, floods, or other causes, upon land not permanently submerged beneath the waters of lakes or seas.(noun)

  source: webster1913