Types of spillways
Spillways are normally “classified” according to their most important aspect: the manner of their control; the flow of their discharge channel and any other details, for example crest alignment. In most large dams, the spillways are controlled, equipped with gates to allow flexible operation. Tunnel spillways are used in places where there is no viability for the adoption of a chute spillway. According to the Hydraulic Design of Spillways, tunnel spillways are routinely designed to work partially filled, with supercritical flow along the entire length. A culvert spillway is normally controlled by a gate and is used when a large flow capacity is required in low head reservoirs. Spillways in orifices are used in the case of arch dams in narrow valleys. A labyrinth spillway has a crest with broken axis, a solution for extending the crest length for a given fixed width available at the site and consequently increasing the spilling capacity of the structure.