Bear-trap gate

Any of a family of crest gates consisting of two leaves, an upstream leaf hinged and sealed at the upstream edge and a downstream leaf hinged and sealed on its downstream edge. The two leaves have a sliding seal at their juncture. When lowered the leaves are in a horizontal position. Gate is raised by admitting water from the forebay into the space beneath the leaves. Probably the first gate operated on the principal of application of headwater pressure.