1) A fence across a stream, probably associated with the flooding of riverside meadows.
The EDD has this word in the sense of a fence across a stream, but only in Somerset. In Yorkshire, the earliest reference occurs in an undated boundary description of the late fifteenth century: so leffe the raw on your leffyd hand to the towyn flodgapp, Bolton by Bowland
1603 the flodgapp in the bancke floshe, Airton. It is likely that the association in these cases is with the flooding of riverside meadows.