--- title: "Daily pondage run-of-river components" subject: "Power Plant Design" chapter: 3 key: "semester_8/power_plant_design:daily-pondage-ror-components" source: https://www.bctengineer.com/q/semester_8/power_plant_design/daily-pondage-ror-components site: BCT Engineering --- # Daily pondage run-of-river components Power Plant Design · Chapter 3: Hydro Power Plant Design - Asked in: 2078 Kartik, 8 marks - Video: [Component of ROR and PROR Hydropower Projects #hydropower #dam#engineering#powerhouse #energy](https://www.youtube.com/watch?v=xwlWEVewQKU) — Hydropower - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/power_plant_design/daily-pondage-ror-components - Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-3 ## Question Discuss major components of a Daily Pondage Run off the River type hydropower project with suitable schematic diagram. ## Short answer A daily pondage ROR project consists of diversion weir with spillway, intake, gravel trap, desander, daily pondage for storing off-peak flow, headrace tunnel, surge tank, penstock, powerhouse with turbine-generator, tailrace, and switchyard. The pond enables peaking operation by storing water during off-peak hours for use during peak demand. ## Answer 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 ```text 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. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the main purpose of the daily pondage in a PROR project? A. Provide seasonal storage for the dry season B. Store off-peak inflow so the plant can generate more during the daily peak C. Remove fine sediment only D. Reduce the head of the plant Answer: B. A PROR stores river water for a few hours each day to give higher output in the 4-6 peak hours. (Key point: Purpose of pondage) 2. What is the role of the desander? A. It absorbs water hammer B. It measures the river discharge C. Fine sediment settles in a slow-flow basin, protecting the turbines D. It raises the water level at the weir Answer: C. A long slow-flow basin lets fine sediment settle and be flushed, which is essential in Nepal to protect turbines. (Key point: Desander role) 3. How is the storage volume of the daily pondage approximated? A. Q_inflow x 24 hours B. Q_design x annual hours C. Q_inflow / Q_design D. (Q_design - Q_inflow) x peak hours Answer: D. The pond must supply the shortfall between design discharge and inflow during the peak period. (Key point: Storage estimate) 4. Which turbine goes with which head in the powerhouse? A. Francis for medium head, Pelton for high head B. Pelton for medium head, Francis for high head C. Kaplan for high head, Pelton for low head D. Francis for low head, Kaplan for high head Answer: A. Francis suits medium heads while Pelton suits high heads. 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