Energy dissipation at the toe of a spillway:

When water flows over a spillway, the kinetic energy of the water is converted into potential energy and dissipated in the form of turbulence and heat at the toe of the spillway. The energy dissipation at the toe of a spillway is affected by various factors such as the flow rate, the slope of the spillway, and the type of energy dissipater used.

Use of hydraulic jump:

Hydraulic jump is a phenomenon that occurs when a high-velocity flow meets a low-velocity flow, resulting in a rapid increase in water depth and a decrease in velocity. Hydraulic jump can be used as an energy dissipater at the toe of a spillway to reduce the velocity and turbulence of the water.

Types of energy dissipaters:

There are various types of energy dissipaters that can be used at the toe of a spillway to dissipate the energy of the water, such as:

1. Roller bucket: A roller bucket is a type of energy dissipater that consists of a series of rollers placed across the width of the spillway. The water flows over the rollers, which create turbulence and dissipate the energy of the water.

2. Ski-jump bucket: A ski-jump bucket is a type of energy dissipater that consists of a curved surface that directs the water upwards and away from the spillway. The water falls onto a sloping surface, creating turbulence and dissipating its energy.

3. Sloping apron taken below the downstream riverbed: A sloping apron taken below the downstream riverbed is a type of energy dissipater that consists of a sloping surface that extends downstream of the spillway. The water flows over the sloping surface, creating turbulence and dissipating its energy.

Conclusion:

Out of the given options, the correct answer is option 'C', i.e., a sloping apron taken below the downstream riverbed. This type of energy dissipater is effective in reducing the velocity and turbulence of the water and dissipating its energy.