billabong vs rivulet

billabong

noun
  • An anabranch, backwater or oxbow lake that is temporarily cut off from the main river, especially one that is only filled with water during the rainy season and can sometimes dry up completely. 

rivulet

noun
  • A small brook or stream; a streamlet; a gill. 

  • Perizoma affinitatum, a geometrid moth. 

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