Spillway

A spillway is a device for protecting Absperrbauwerken (eg dams, dams ) from unexpectedly high water levels in hydraulic engineering.

The spillway comes into operation when the water level of a Absperrbauwerks the storage level - mostly due to increased lying out of order water entries - exceeds. It protects the locking mechanism against excessive exposure to the increased water pressure and to prevent the overflow of water over the barrier, since these could in the worst case failure of the barrage. The spillway must be designed for the maximum flood ( design flood ).

The spillway consists of an inlet, an extension line (including transportation ) and an energy conversion building ( mostly the stilling basin of the main outlet of the barrage ).

Construction types

Raid

During an attack, the water is after reaching the target storage controlled by the dam or derived laterally therefrom. In dams overflow is usually performed as a lateral flow near the barrage and based on mature (ie undisturbed ) soil. This is especially so since a guided over the dam overflow due to the expected settlement of embankment more difficult, as movable, must be constructed. After overflow, the excess water through a flume (often implemented as a cascade) side of the dam to drain the dam derived. At the bottom of the valley, the water flows through generally still a stilling basin, where the kinetic energy of the water is largely converted: the water is taken by the high speed before it enters the watercourse of the lower water.

In dams, the flood is drained more frequently than in dams over the barrage. The excess water flows in this type of spillway at predefined locations on top of the wall, or are provided in the wall openings. On the air side of the wall, the water is then brought down and enters the area of ​​the wall foot in the stilling basin.

The attack can be carried fixed or movable. Thus, for example, a weir trap, with the height of the accumulated in the total storage space water is controlled to be installed.

Spillway storm

Another construction is the spillway storm. This is the space available in the storage system, and often has an overflow in the form of a raid funnel. For this reason he is also referred to as a chalice, tulip or trumpet. Exceeds the water level of the dam, the water level, the excess water flows into the overflow. By the tower and then pipe or tunnel system, the water is introduced into the flow through the dam below the dam.

Active Spillway

In contrast to the raid and the spillway storm, where the high water can be discharged using the spillway only when the water level has been exceeded, there are also systems that can be described as "active" spillway. In the active spillway the intake structure is located below the water line of the storage target and is closed by a gate valve in the normal case.

This type of spillway is sometimes used in dams, where the intake structure is often integrated into the locking mechanism. When flooding is imminent, the shutter is opened and the water flows through pipes in the dam to the air side, where it is fed via a spillway chute a subsequent jump. The hill throws the water in a high arc into the stilling basin, from which it continues to flow into the natural waters.

The intake structure but can also be installed in either the dam enclosing valley sides. In this case, the water flows after opening the lock slide through tunnels on the other side of the dam, where it is also fed via a spillway chute and a subsequent entrenchment of the natural waters.

An example of a spillway by means of a hill is the Cahora Bassa Dam in Mozambique.