Place found in rickety pier causing undulation (6)
I believe the answer is:
ripple
'undulation' is the definition.
(thesaurus)
'place found in rickety pier' is the wordplay.
'place' becomes 'pl' (I've seen this in other clues**).
'found in' means one lot of letters goes inside another.
'rickety' indicates an anagram.
'pier' with letters rearranged gives 'ripe'.
'pl' put inside 'ripe' is 'RIPPLE'.
'causing' acts as a link.
(Other definitions for ripple that I've seen before include "undulation" , "Small wave on the surface of a liquid" , "Edgar Allan ---, US author" , "bit of applause maybe" , "Slight surface wave" .)