High dam hydropower project components

A high dam type project uses a tall dam (usually above about 15 m, often 100 m or more) to create a large head and storage reservoir; the powerhouse is placed at the toe of the dam or at the end of a short waterway.

 Reservoir  ~~~~~~~~~~|\
 ~~~~~~~~~~~~~~~~~~~~~| \  High dam
 Intake (trash rack)->|==\====\
                      |   \    \ Penstock
                      |____\    \
                     Spillway  [Powerhouse]
                                Turbine-Gen
                                   |    |
                            Tailrace  Transformer
                                   |    |
                                River  Switchyard

Major components

1. High dam: concrete gravity, arch or rockfill/earthfill; creates head and storage. It must be safe against overturning, sliding and seepage.
2. Reservoir: live storage between full supply level and minimum operating level; dead storage for sediment.
3. Spillway and energy dissipator: pass floods safely and protect the riverbed below.
4. Intake: at the dam face or in a tower, with trash rack and gates, placed above sediment level.
5. Bottom outlet / sluice: to flush sediment and empty the reservoir.
6. Penstock: short pressure pipe through or around the dam to the turbines (surge tank needed only if the waterway is long).
7. Powerhouse: at the dam toe; contains turbines (usually Francis), generators, governors and auxiliaries.
8. Tailrace: returns water to the river.
9. Electrical works: step-up transformer, switchyard and transmission line.

Example: the proposed Budhigandaki (about 1200 MW) and Kulekhani reservoir in Nepal; worldwide, Three Gorges and Tehri.

Advantages and limitations

• Gives large head with a short waterway, firm power through the dry season, peaking capacity and flood control.
• Needs very high investment and long construction time, causes submergence and resettlement, and loses storage to sedimentation, which is serious in Himalayan rivers.