Riverbank deposit (4)
I believe the answer is:
silt
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">riverbank deposit</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for silt that I've seen before include "Material deposited by a river" , "Mud deposits in a river" , "Slimy mud" , "Fine sediment (often deposited by water)" , "Sedimentary material" .)