Pipe coming from river is eroding (5)
I believe the answer is:
riser
'pipe' is the definition.
(I know that riser is a type of pipe)
'coming from river is eroding' is the wordplay.
'coming from' indicates the answer is hidden within the clue.
'RISER' is hidden in the letters of 'river is eroding'.
(Other definitions for riser that I've seen before include "Upright piece between steps" , "Vertical piece between two stair treads" , "One who has stopped sleeping" , "Upright part of stair step" , "Front of a staircase step" .)