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A spillway gate, also known as a stop gate, serves as an adjustable barrier regulating the flow of water in rivers, streams, and reservoirs. Its primary function involves controlling water flow while also acting as a barrier to store additional water when needed. These flow control gates facilitate the safe and controlled passage of excess water around, over, and through a dam. Let's explore the various types of spillway gates and their diverse applications.
There exist multiple types of spillway gates, each designed for specific purposes within dams. This article will delve into the functionality of spillway gates and their operational mechanisms.
Spillway gates play a crucial role in regulating the volume of water entering reservoirs or rivers. They achieve this by managing the size of the opening between the gate and the reservoir. A smaller opening allows more water to flow into the reservoir, while closing the gate forms a barrier between the reservoir and the river, limiting the water intake.
These gates operate through various mechanisms tailored to their specific functions. There are primarily three methods by which spillway gates function: gravity, hydraulics, and mechanical. Gravity-based gates utilize gravitational force for movement, hydraulic gates rely on hydraulic power, and mechanical gates are operated by motors. Each type has its unique mode of operation suited to its purpose.
These gates function on the principle of gravity. They are typically found in gravity dams, where the gate's weight causes it to lower. As the gate descends, it creates an opening between the upstream and downstream sections, enabling the unrestricted flow of water between them.
This type of gate utilizes hydraulic power for its operation. It comprises two chambers separated by a diaphragm: one chamber contains air while the other holds water. When the valve is shut, air fills the water chamber, generating an air bubble that exerts pressure on the diaphragm. This pressure causes the diaphragm to rise, opening the valve. Upon opening, the air bubbles exit the water chamber, halting the diaphragm's downward force and consequently closing the valve.
Operating with motors, these gates move back and forth as directed by the motor's action. The gate halts when fully closed, with the motor ceasing movement. Conversely, when the gate reaches complete openness, the motor recommences its motion.
There are a range of different spillway gates that you may come across. Here at BIC's, we have vast experience with working with all of these different types of spillway dams.
The most common type of spillway gate is a sluice gate. It consists of two parts: an upstream part and a downstream part. Both parts are connected with each other via a hinge. The upstream part has a small hole on its top edge. Water flows through the hole and down into the downstream part. The downstream part has a large hole at the bottom edge. Water then flows out of the downstream part and into the reservoir. If you want to open the gate, you need to lift the upstream part so that it releases the water. Then you can lower the downstream part so that it closes the gap between the upstream and downstream part.
Another kind of spillway gate is called a slide gate. It works similar to a sluice gate, but instead of having a hole on the top edge of the upstream part, it has a slot. You can see the difference below:
The advantage of a slide gate is that it does not require any lifting mechanism. All you need to do is slide the upstream part along the downstream part until it reaches the desired position.
The crest gate employs a bottom-hinged flap to manage water levels, boasting a more streamlined and compact design constructed on a fixed axis.
Usually operated hydraulically, these gates offer reliability during power outages or flood events. They operate by rotating on their hinges, facilitating both opening and closing actions. This gate proves to be an optimal choice for allowing the passage of various materials downstream, including ice, making it versatile for diverse situations.
Positioned at the crest of a dam, the radial gate serves to increase the dam's overall water retention capacity. Its primary function is to regulate and maintain optimal water levels. This gate operates with minimal effort for opening or closing. The pressure exerted on the curved face of the gate transmits through the support beams into the curved arms, providing enhanced resistance.
Also known as canal lock or lock gates, miter gates consist of two leaves that seal one end of a lock, forming an angled barrier against the stream. They control the ingress and egress of water within the lock, facilitating water flow through the system. These gates facilitate the adjustment of water levels in the lock and remain in widespread use in modern waterways and canals.
A drum gate is a hollow structure floating on the water's surface, designed to pivot up or down. Hinged horizontally at the top of a dam within a cylindrical structure, it can be elevated to allow increased water intake. These gates are ideal for precise control over reservoir water levels.
Spillway gates serve multiple purposes based on their types. Some common applications include:
Preventing Reservoir Flooding: These gates are crucial in averting flooding caused by water levels surpassing the dam's height. Operators employ spillway gates to manage and prevent such occurrences.
Regulating Water Levels: Particularly near urban areas, maintaining lower water levels is vital to prevent harm to people in the event of a dam breach. Spillway gates aid in this regulation.
Erosion Protection: Dams near rivers and streams might cause erosion. Spillway gates, exemplified by the Grand Coulee Dam in Washington State, help counteract this soil erosion by controlling water pressure.
Storing Excess Water: Reservoirs created by dams collect rainwater, snowmelt, and river runoff. Spillway gates regulate the influx of water into these reservoirs.
Water Release During Repairs: Operators may release stored water behind a dam during repair or reconstruction processes.
Mitigating Soil Erosion Risks: In areas prone to soil movement, spillway gates are utilized to minimize potential soil erosion if the dam were to fail.
Controlling Water Flow: Operators can redirect water flow using spillway gates, altering its direction and releasing specific amounts of water as needed.
Preventing Lake Overflow: Near lakes, spillway gates are employed to regulate water levels, preventing potential damage to surrounding land in the event of an overflow.
These diverse applications illustrate the significance of spillway gates in managing water levels, safeguarding against damage, and controlling the flow of water within dam systems.
In the selection of the spillway gate type, it’s also important to adapt the characteristics of the gate to the operating requirement of the hydraulic structure like discharge capacity, loads on the concrete structure, absence of vibration, hydraulic regulation, and many others.
