Like some waters initially lapping mine entrance when rising (5)
I believe the answer is:
tidal
'like some waters' is the definition.
'initially lapping mine entrance when rising' is the wordplay.
'initially' suggests taking the first letters.
'mine entrance' becomes 'adit' (I've seen this before).
'when rising' says the letters should be written backwards.
The first letter of 'lapping' is 'l'.
'l'+'adit'='ladit'
'ladit' back-to-front is 'TIDAL'.
(Other definitions for tidal that I've seen before include "Type of wave" , "Subject to moon's pull" , "Concerning regular changes in sea level" , "Subject to ebb and flow" , "going with the flow" .)