1. weir: a dam erected across a river to raise the level of the water. A fence of stakes set in a river or along the shore as a trap for fish. The word is now restricted to smaller works, the larger are called dams. (IHO Dictionary, S-32, 5th Edition, 5967)
  2. dam: a barrier to check or confine anything in motion; particularly one constructed to hold back water and raise its level to form a reservoir, or to prevent flooding. (IHO Dictionary, S-32, 5th Edition, 1196)
  3. flood barrage: an opening dam across a channel which, when required, is closed to control flood waters. (IHO Chart Specifications, S-4 326.7)