The correct answer is D. shaft spillway.
A shaft spillway is a type of spillway that is constructed as a vertical or near-vertical shaft. It is typically used in conjunction with an embankment dam to provide a means for excess water to be discharged safely. Shaft spillways are not typically used in earthen dams because they are expensive to construct and can be difficult to maintain.
Ogee spillways are the most common type of spillway used in earthen dams. They are designed to dissipate the energy of the water as it flows over the spillway, thereby reducing the risk of erosion and damage to the dam. Chute spillways are similar to ogee spillways, but they have a steeper slope. This allows them to handle larger flows of water than ogee spillways. Side channel spillways are located on the side of a dam and are designed to divert excess water away from the dam. They are typically used in conjunction with other types of spillways, such as ogee or chute spillways.
In conclusion, the correct answer is D. shaft spillway. Shaft spillways are not typically used in earthen dams because they are expensive to construct and can be difficult to maintain.