catchment vs plunge pool

catchment

noun
  • Any structure or land feature which catches and holds water; the collection of such water. 

  • A catchment area, or the people it serves. 

verb
  • To divide into catchment areas. 

plunge pool

noun
  • A pool that is small in diameter, but deep, usually resulting from erosion by a natural force such as a waterfall or rapids. 

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