Positive surge

When the hydraulic jump is in a moving form, it is called positive surge. This phenomenon occurs when a supercritical flow suddenly transitions to a subcritical flow, resulting in a rapid increase in flow depth and a decrease in flow velocity. The positive surge is characterized by the formation of a standing wave or hydraulic jump.

Understanding hydraulic jump

A hydraulic jump is a sudden change in flow characteristics that occurs when a high-velocity flow encounters a lower-velocity flow or an obstruction. It is a common phenomenon observed in open channel flows, such as rivers, spillways, and culverts.

When the flow transitions from supercritical to subcritical, there is a rapid decrease in flow velocity, accompanied by an increase in flow depth. This sudden change in flow properties leads to the formation of a hydraulic jump. The hydraulic jump helps dissipate the excess energy in the flow and reduces the flow velocity, preventing erosion and damage downstream.

Types of hydraulic jump

There are two main types of hydraulic jumps: positive surge and negative surge.

1. Positive surge:
- Occurs when the hydraulic jump is in a moving form.
- Associated with a sudden increase in flow depth and a decrease in flow velocity.
- The flow transitions from supercritical to subcritical, forming a standing wave or hydraulic jump.
- Positive surge is commonly observed in high-energy flows, such as spillways and rapids.

2. Negative surge:
- Occurs when the hydraulic jump is in a retreating form.
- Associated with a sudden decrease in flow depth and an increase in flow velocity.
- The flow transitions from subcritical to supercritical, resulting in a wave-like motion.
- Negative surge is commonly observed in low-energy flows, such as gradually sloping channels.

Importance of understanding positive surge

Understanding positive surge is crucial in the design and operation of hydraulic structures. By recognizing and analyzing the occurrence of positive surge, engineers can ensure the stability and safety of hydraulic systems. Hydraulic jumps, including positive surge, affect the energy dissipation, flow characteristics, and sediment transport in open channel flows. Therefore, accurate prediction and control of hydraulic jumps are essential for efficient water management and flood control.