Diversion type storage plant characteristics

A diversion-type storage plant has a dam that creates a reservoir, but the water is taken from the reservoir by a tunnel or canal and carried to a powerhouse located away from the dam, often in another valley or far downstream. This gives extra head beyond the dam height.

Plan
      Reservoir
   ~~~~~~~~~~~~|Dam|--Spillway
   ~~~~~~~~~~~~|   |
   Intake ---->+   |
        \
         \== Headrace tunnel ==+ Surge tank
                               |  Penstock
                               PH --> Tailrace --> River
Section
 FSL ~~~~|dam
    Intake\______ tunnel _______(ST)
                                  \ penstock
                                   \__PH

Principal characteristics

• A dam stores water for seasonal regulation, so firm power is available throughout the year.
• The head is the sum of the dam head and the drop gained along the river course through the tunnel; the powerhouse is not at the dam.
• Main components: dam with spillway and bottom outlet, intake with trash rack and gates, headrace tunnel, surge tank, penstock, powerhouse, tailrace and switchyard.
• The tunnel runs under pressure, so the river bend between the dam and the powerhouse is bypassed. The river reach between them has reduced flow (an environmental flow is required).
• It needs a high capital cost and a long construction time, but gives a large capacity and good peaking.
• Example: Kulekhani I (Nepal), where the Kulekhani dam forms the Indra Sarobar reservoir and the water is carried by tunnel and penstock to a powerhouse at Dhorsing, far below. Kaligandaki A has a similar diversion layout (dam, long headrace tunnel, distant powerhouse), but with only daily pondage.