Alluvion a legal term which describes the increase in the area of land due to sediment (alluvium) which is deposited by a river. Alluvium (from the Latin, alluvius, from alluere, "to wash against" is Soil or Sediments deposited by a river or other running This changes the size of a piece of land (a process called accession) and thus its value over time. Accession (from Lat accedere, to go to to approach in Law, a method of acquiring Property adopted from Roman law (see Accessio