intertidal zone vs riverbank

intertidal zone

noun
  • The part of a shore between high water and low water, especially the beach exposed at maximum ebb spring tides. 

riverbank

noun
  • A sloped side of a river acting as a barrier between the water and level ground to either side. 

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