The correct answer is: C. 1.25 hw
Freeboard is the vertical distance between the highest water level anticipated and the top of the dam. It is an important safety feature that helps to prevent overtopping of the dam during floods.
The height of the wave is a major factor in determining the required freeboard. The higher the wave, the greater the risk of overtopping. Therefore, the freeboard is typically set to be at least 1.25 times the height of the wave.
This value is based on engineering standards and experience. It is designed to provide a safe margin of error in the event of a flood.
The other options are incorrect because they do not provide a sufficient margin of safety. A freeboard of 0.5 hw would only be appropriate for very small waves, while a freeboard of 1.5 hw would be excessive for most situations.
In conclusion, the maximum height of freeboard for wave action in dams is generally taken to be equal to 1.25 hw. This value is based on engineering standards and experience, and it is designed to provide a safe margin of error in the event of a flood.