low water vs subsidence

low water

noun
  • The lowest stage of a river. 

  • The temporary situation of having little money. 

  • The location of low tide in a coastal area. 

subsidence

noun
  • A sinking of something to a lower level, especially of part of the surface of the Earth due to underground excavation, seismic activity or underground or ground water depletion. 

  • The process of becoming less active or severe. 

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