Tide Gates

Tide Gates serve to drain tidelands (areas that incoming tides regularly cover) for agricultural or other uses.  First a dike is built to isolate the area to be drained.  A large pipe or culvert passes through the dike.  On tidewater side of the pipe there is a hinged door which opens outwards towards the bay or estuary.   When water levels are higher on the side of the pipe towards the drained area, the weight of the water holds the door open, allowing water to flow out into the bay or estuary.  When the tide rises, the level of water on the tidewater side becomes higher than on the drained area side, holding the door closed so water does not flow back into the drained area.

Drained areas are typically not totally dry and have small streams or marshes that are potential habitat for small fish.  With traditional tide gates, passage of fish and water between the tidewater and the drained area is limited.  This leads to stagnant water and fish being excluded from the habitat or trapped on the drained side when they wish to leave.

Modified tide gates use floats or other devices that hold the gate open until the water on the drained side reaches a particular level, and then it closes.  This allows a longer period when the gate is open so water can be exchanged and fish may enter or leave the habitat in the drained area.

old style tidegate