alluvion vs superfluity

alluvion

noun
  • The increase in the area of land due to the deposition of sediment (alluvium) by a river. 

superfluity

noun
  • The quality or state of being superfluous; overflowingness. 

  • Something superfluous, as a luxury. 

  • Collective noun for a group of nuns. 

How often have the words alluvion and superfluity occurred in a corpus of books? (source: Google Ngram Viewer )