The fixed overflow weir operates based on the weir flow principle: when a barrier (weir) is installed in an open channel, water flows over the barrier’s top. As a common hydraulic structure, it primarily controls water flow for purposes like flood control, irrigation, navigation, and power generation. It features a fixed overflow height—when the water level exceeds this height, water flows smoothly over the weir top and continues downstream.
Working Principle
Overflow: When the upstream water level rises above the weir top, water starts to overflow and flow down the weir surface. Here, the weir resists the flow, reducing its speed and altering its direction.
Flow control: The weir regulates flow via its fixed top height. With low upstream water levels, water does not overflow but flows through other channels/pipes. When levels exceed the weir top, overflow occurs. Adjusting the weir height enables precise flow control.
Energy conversion: During overflow, part of the water’s kinetic energy converts to potential energy, and the flow encounters resistance. This conversion and consumption of energy help control and regulate the water flow.
Types and Characteristics
Types: Classified by shape and use (e.g., thin-walled weirs, wide-top weirs), each with specific applications, advantages, and limitations.
Characteristics: Simple structure, easy maintenance, and precise flow control. It adapts to varying flow conditions and water level changes, ensuring stable, orderly overflow.
Application Examples
Widely used in water conservancy projects and urban drainage systems:
In water conservancy: Controls reservoir discharge to keep reservoirs within safe water levels.
In urban drainage: Regulates rainwater runoff peaks, reducing the size and cost of downstream drainage ditches.
