737. Unusual Alleys
Shabbos 17:4
If an alley is level but slopes down to a public domain, or if the entrance to the public domain is level but the alley itself slopes down, it does not require a pole or a beam to permit carrying because it is already distinguished from the public domain.
Shabbos 17:5
If one side of an alley ends at the sea and the other side ends at a public trash heap, nothing further need be done to permit carrying in it. This is because a public trash heap is unlikely to be removed and we are not concerned with the remote possibility that the sea will wash up detritus that will form a surface level to the alley.