In a shaft spillway, the water from reservoir enters into vertical shaft which conveys water into a horizontal tunnel which finally discharges the water into the river downstream. For small shafts may be constructed entirely for metal or concrete

1. Syphon Spillway

It consists of a siphon pipe, one end of which Skepton upstream side and in contact with theReservoir while other end discharges water on downstream side.

ENERGY DISSIPATION BELOW SPILLWAYS

Since spillways are high structures, the water flowing over them has considerable velocity and kinetic energy due to conversion of potential energy into kinetic energy when it reaches the river bed and this has to be destroyed before the water is allowed to flow over the river bed, because otherwise there will be considerable erosion of bed at the toe of the spillway endangering the stability of the structure. The devices provided for destroying the energy of water flowing over the spillways are termed as 'dissipators'. The energy dissipation arrangementdepends on the consideration of the nature of the device to be employed and the character of the river bed downstream.

Selection of Energy Dissipators

Various considerations governing the selection of energy dissipator are discussed below:

1. Type of dam and spillway. In earthen dam a chute spillway can be provided with hydraulic jump basin with or without baffles or end sills. In an arch dam, free fall spillway with stilling pool of high depths in normally provided.