Daily pondage run-of-river components

A daily pondage run-of-river (PROR) project stores river water for a few hours each day in a small pond so the plant can generate more during the daily peak load. It has all ROR components plus the pondage.

Schematic

 River ==|== Weir/dam + spillway + undersluice
         |
       Intake ---> Gravel trap ---> Desander
                                       |
                              [ DAILY PONDAGE ]
                                       |
                              Headrace tunnel/canal
                                       |
                                 Surge tank/forebay
                                       |
                                    Penstock
                                       |
                         Valve -> Turbine -> Generator
                                       |        |
                                   Tailrace   Transformer
                                       |        |
                                     River   Switchyard

Major components

1. Headworks: diversion weir or low dam to raise water level; gated spillway for floods; undersluice to flush sediment away from the intake.
2. Intake: side or frontal intake with trash rack and gates to admit design discharge.
3. Gravel trap: removes gravel and coarse sand near the intake.
4. Desander (settling basin): long, slow-flow basin where fine sediment settles; flushed periodically. Essential in Nepal to protect turbines.
5. Daily pondage: small reservoir (or enlarged desander/forebay) that stores the off-peak inflow. Storage needed $\approx (Q_{design} - Q_{inflow}) \times$ peak hours. It lets a dry-season plant give full output for about 4–6 peak hours.
6. Headrace tunnel or canal: carries water to the surge tank/forebay with small head loss.
7. Surge tank (or forebay): absorbs pressure surges and supplies water during sudden load increase.
8. Penstock: steel pressure pipe with anchor blocks; valve at the top for emergency closure.
9. Powerhouse: turbine (Francis for medium head, Pelton for high head), generator, governor, excitation, cooling and control systems.
10. Tailrace: returns water to the river.
11. Electrical works: step-up transformer, switchyard and transmission line to the grid.

Advantages

Higher peak capacity and revenue than plain ROR, better match with Nepal's evening peak, and much smaller submergence than a storage project. Examples in Nepal: Kaligandaki "A", Middle Marsyangdi and Upper Tamakoshi are peaking ROR projects.