What is a head in a micro hydro power plant?

The correct answer is option 4):(The head is the vertical distance of the waterfalls.)

Concept:

• Micro head power plants are the small power plant with an installed capacity of less than 100 kW
• It is a run river hydroelectric plant. There are no requirements for large dams
• It is a decentralized, robust and simple technology
• These installations can provide power to an isolated home or small community or are probably  connected to electric power networks
• The fundamental components of Micro head power plants include the dam, penstock, turbine, tailrace, generator, and allied equipment.
• Head is the height difference between the water entry into the hydro system, such as the weir or intake scene, and the discharge, in meters
• Head is the change in water levels between the hydro intake and the hydro discharge point. 
• For a micro hydel power plant the head is the vertical distance the waterfalls.
• The micro head plant is shown in fig:​