fenland vs polder

fenland

noun

  • a kind of low-lying ground, often wet or marshy 

polder

noun

  • An area of ground reclaimed from a sea or lake by means of dikes. 

verb

  • To reclaim an area of ground from a sea or lake by means of dikes. 

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