lock gate

lock gate (plural lock gates)

1. (Usually) one of a pair of gates at each end of a lock chamber on a canal, or river with a weir.
   • 1961 January, “Talking of Trains: Flooding at Lewes”, in Trains Illustrated, page 5:

     During the day conditions worsened quickly—for example, a 2-6-0 on the Uckfield line suddenly encountered flood water high enough to enter its ashpan and extinguish its fire—until lock gates up-river at Barcombe gave way and a tidal wave rolled down the valley meeting head-on a spring tide rolling up from the coast.