How do tide gates drain coastal land while keeping seawater out?

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Yser River; land reclamation — land reclamation The Yser River flowing through reclaimed farmland in Belgium.

A tide gate is a specialized structure used in land reclamation and coastal management to control water movement. It functions as a one-way valve that allows water to flow in only one direction.1

When the tide is low and the water level on the landward side is higher than the sea level, the pressure forces the gate open, allowing accumulated water to drain out into the ocean. Conversely, as the tide rises and the sea level exceeds the water level on the landward side, the pressure pushes the gate shut automatically. This mechanism effectively prevents seawater from entering and flooding the reclaimed coastal land.1