Rising water regularly this deep (4)
I believe the answer is:
tide
'rising water regularly this deep' is the definition.
'tide' can be an answer for 'deep' (thesaurus). I'm not sure about the rest of the definition.
'regularly this deep' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'this'+'deep'='thisdeep'
The alternate letters of 'thisdeep' are 'TIDE'.
Can you help me to learn more?
(Other definitions for tide that I've seen before include "Periodic water movement" , "Periodic flow" , "Powerful surge" , "Something going in and out" , "It ebbs and flows" .)