Physical

• Geologically stable areas (e.g. away from earthquake zones): To ensure dam is stable and secure with solid stable rock foundations to hold weight of the dam (e.g. granite)
• Rock type: Metamorphic rock (e.g. slate) = impermeable, some rock (e.g. sandstone) is permeable leading to seepage (undesirable)
• Deep Narrow valley cross section behind the dam: To reduce dam length, reduce cost of building, maximise storage and reduce surface area to keep evaporation levels low
• Cool climate: To keep evaporation lower than precipitation
• Constant supply of water to reservoir (rain and snow melt): To ensure the dam has a consistent water supply throughout the year
• High drainage density: Increases efficiency of water collection
• Vegetation: To stabilise the sides of the valley