catchment vs nullah

catchment

noun
  • A catchment area, or the people it serves. 

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

verb
  • To divide into catchment areas. 

nullah

noun
  • A stream-bed, ravine, or other watercourse; a drain for rain or floodwater. 

  • An open-air, concrete-lined channel for draining rain or wastewater. 

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