A surge or surge wave is a moving wave front which brings about an abrupt change in depth of flow.
A surge may be caused by various factors such as closer or opening of valves or gates, loading or unloading of turbines, start or stopping of pumps, failure of dams leading to flow of reservoir downstream etc.
A surge is also often referred to as moving hydraulic jump and is caused by sudden increase or decrease in flow. Surges are classified as:
Positive surge: It is the one which results in an increase in depth of flow.
Negative surge: It is the one which causes a decrease in the depth of flow.
Based on the movement of the surge either upstream or downstream, the various types of surges are:
Type A: It may occur when a gate provided at the head of a channel is suddenly opened.
Type B: It may occur when a gate provided at the tail end of a channel is suddenly closed.
Type C: It may occur when a gate provided at the head of a channel is suddenly closed.
Type D: It may occur when a gate provided at the tail end of a channel is suddenly opened.
