Functioning Principle of Fusegate

The Fusegate System is based on the following concept:

o   Fusegates are free-standing units installed side by side on a spillway sill to form a watertight barrier.

o   They bear against small abutment blocks set in the sill to prevent them from sliding before they are required to rotate (under extreme flood conditions).

There is a chamber in the base of each Fusegate, with drain holes to discharge incidental inflow (due to leaking seals for example).

Figure 1: C/S through a fusegate with moderate overspill.

Figure 2: C/S through a fusegate with inlet well being fed.

Figure 3: Uplift pressure cause the fusegate to overturn

An inlet well on the upstream side of the Fusegate crest discharges water into the chamber when the headwaters reaches a predetermined level. (Well lips on individual Fusegates are actually set at different levels).

During very large floods, water entering the chamber over the inlet well causes an uplift pressure to develop in the chamber.

The uplift pressure, combined with the hydro-static pressure (acting from left to right on the adjacent diagram) is sufficient to overcome the restraining forces and the imbalance causes rotation of the unit off the spillway. The Fusegate is then washed away clear of the spillway by the flood.

If the water level continues to rise after the first breach more Fusegates can rotate, all according to pre-determined upstream water levels until eventually there are no more units remaining and the spillway is free to pass the original maximum design flood. Until rotation of the first Fusegate, (for floods of extremely low risk of occurrence), the user has the benefit of the additional storage.

Each Fusegate has a different overturning level, precisely determined by the height of the water inlet and its own unique stability.

Fusegates System

Fusegates are an innovative and reliable spillway system patented by Hydroplus. Fusegate system consists of a set of independent units placed on weir sill to form a watertight barrier.  They represent genuine alternative to conventional system, such as gates, flaps or inflatable tubes. Fusegates have successfully been implemented on 40 dams throughout the world, providing solid evidence of their value and effectiveness.

Fusegates are modular freestanding units that can be installed side by side on a spillway’s modified sill (the sill must be levelled to provide the necessary flat structure to accommodate the Fusegate modules). The modules consist of a vertical facing connected to a horizontal slab atop the sill. Watertight seals around the upstream perimeter of each Fusegate make it complete waterproof. Each unit rests on abutment blocks on top of the sill and is weighted with ballast to resist hydrostatic pressure (see figure).

Benefits of this system:

• Greater flexibility of operation
• Low maintenance of Fusegate system
• No human involvement in operation
• Lowest risk of malfunctioning
• Enhance dam safety
• Maximum overflow depth is 140% of Fusegate height
• Fusegate system is a non-mechanical
• Minimize the potential for mechanical gate failure
• To recover up to 2/3^rd of the distance between the ungated sill and crest of the dam without raising M.W.L.

Normal operation:

Installed a top the spillway, Fusegates form a watertight screen and raise the dam’s crest. For most floods, water is discharged over the Fusegates, which act as a free-sill spillway.

Major flooding:

A Fusegate’s pressure chamber starts to fill when the water level exceeds the crest of the inlet well. As soon as drain holes reach their saturation point, pressure under the Fusegate lifts the unit and tips it in the downstream direction. As water rises, Fusegates overturn in sequence. Their tipping points are carefully set to produce this controlled, sequential action.

For More details visit: www.hydroplus.com