Bank deposit (4)

I believe the answer is:
silt
'bank deposit' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for silt that I've seen before include "Mud deposit in a river" , "Material deposited by a river" , "Mud deposits in a river" , "Slimy mud" , "Sediment deposited in channel or harbour" .)