SU 5355 is the wall of a drainage channel formed also by 5518, 5519, 5520 on the other, eastern side of 5417. The channel cuts through this ashlar wall, which must have been out of use when it was constructed. The gap in the north leads to a square cut in the bedrock, now filled with modern concrete, possibly also associated with water movement. This then joins the cut (SU 5418) for 5417 - if water drained through here, 5417 must certainly have been out of use.