When selecting a site for a hydroelectric power plant, the following factors are essential:
1. Large catchment area: Ensures a sufficient amount of water flow to generate power.
2. Rocky land: Provides a stable foundation for constructing the dam and other infrastructure.
3. Availability of water: Ensures there is a reliable water source to drive the turbines.
Sedimentation is not a requirement for site selection. In fact, excessive sedimentation can be harmful as it may reduce the capacity of the reservoir and affect turbine performance over time.
Thus, the correct answer is Sedimentation.