Spillway
In this case, the dam is not designed to function with water flowing over the top if it, either due to the materials used for its construction or conditions directly downstream.
If inflow to the reservoir exceeds the gate's capacity, an artificial channel called an auxiliary or emergency spillway will convey water.
If present, the fuse plug is designed to wash out in case of a large flood greater than the discharge capacity of the spillway gates.
Although many months may be needed for construction crews to restore the fuse plug and channel after such an operation, the total damage and cost to repair is less than if the main water-retaining structures had been overtopped.
A chute spillway is a common and basic design that transfers excess water from behind the dam down a smooth decline into the river below.
Chute spillways can be ingrained with a baffle of concrete blocks but usually have a "flip lip" and/or dissipator basin, which creates a hydraulic jump, protecting the toe of the dam from erosion.
[2] Despite being superseded by more modern engineering techniques such as hydraulic jumps in the mid twentieth century, since around 1985[3] interest in stepped spillways and chutes has been renewed, partly due to the use of new construction materials (e.g. roller-compacted concrete, gabions) and design techniques (e.g. embankment overtopping protection).
[7][8] Research is still active on the topic, with newer developments on embankment dam overflow protection systems,[8] converging spillways[9] and small-weir design.
The highest morning glory spillway in the world is at Hungry Horse Dam in Montana, U.S., and is controlled by a 64-by-12-foot (19.5 by 3.7 m) ring gate.
The largest bell-mouth spillway is in Geehi Dam, in New South Wales, Australia, measuring 105 ft (32 m) in diameter at the lake's surface.
A drop inlet resembles an intake for a hydroelectric power plant and transfers water from behind the dam directly through tunnels to the river downstream.
The magnitude of the SDF may be set by dam safety guidelines, based on the size of the structure and the potential loss of human life or property downstream.
The return period is set by dam safety guidelines, based on the size of the structure and the potential loss of human life or property downstream.
Operating protocols may require "cracking" a gate to release a small amount of water to warn persons downstream.
