What is the primary function of a flap gate?

The primary function of a flap gate is to prevent reverse flow of water. Flap gates are designed to allow water to flow in one direction while automatically closing to block water from flowing back in the opposite direction. This mechanism is crucial in various applications, such as in drainage systems where backflow could cause flooding or contamination. When water pressure from the downstream side exceeds that of the upstream side, the flap closes, effectively preventing any reverse flow. This property is especially valuable in stormwater management systems and other hydraulic systems where maintaining the intended flow direction is important for functionality and environmental protection.

While other functions like regulating water temperature, allowing free passage of aquatic life, or discharging excess water pressure might be relevant in other contexts, they do not accurately describe the primary purpose of a flap gate, which is focused explicitly on controlling the flow to prevent backflow.