**Answer:**

The ogee spillway is the least suited spillway for earthen dams. Here's why:

**1. Ogee Spillway:** The ogee spillway is a type of overflow structure commonly used in concrete dams. It consists of a curved crest that helps in dissipating the energy of the flowing water. However, this type of spillway is not suitable for earthen dams due to several reasons:

- **Structural Stability:** Earthen dams are made of compacted soil and are generally less rigid compared to concrete dams. Ogee spillways are designed to be built on solid foundations and require a substantial amount of structural support. The inherent flexibility and settlement potential of earthen dams may lead to structural instability and potential failure if an ogee spillway is constructed.

- **Sediment Transport:** Earthen dams are often constructed across rivers to impound water and control the flow. These rivers often carry a significant amount of sediment, such as sand and silt. The ogee spillway is not well-suited for handling sediment-laden flows. The curved crest and the energy dissipating features of the spillway may cause sediment deposition and clogging, leading to reduced spillway capacity and potential dam safety issues.

- **Maintenance and Operation:** Ogee spillways require regular inspection, maintenance, and operation to ensure their proper functioning. The maintenance of an ogee spillway in an earthen dam can be challenging due to the access constraints and the potential for erosion and instability of the surrounding earthen materials.

**2. Other Spillway Options:** While the ogee spillway is not suitable for earthen dams, there are other spillway options that are commonly used:

- **Side Channel Spillway:** This type of spillway diverts the flow of water through a separate channel located adjacent to the dam. It is well-suited for earthen dams as it provides a controlled path for the water to flow around the dam without compromising its stability.

- **Chute Spillway:** A chute spillway is a steep, open channel that allows water to flow down a slope and safely discharge downstream. This type of spillway can be constructed with earthen materials and is suitable for controlling the flow from earthen dams.

- **Shaft Spillway:** A shaft spillway is a vertical or inclined conduit that allows water to be discharged from the dam through a submerged orifice. While less common, it can be a suitable option for earthen dams depending on the site conditions and design requirements.

In summary, the ogee spillway is least suited to earthen dams due to its structural requirements, potential for sediment deposition, and maintenance challenges. Other spillway options, such as side channel spillways, chute spillways, or shaft spillways, are better suited for earthen dams considering their design and operational requirements.