--- title: "ROR versus PROR hydropower plants" subject: "Power Plant Design" chapter: 3 key: "semester_8/power_plant_design:ror-vs-pror" source: https://www.bctengineer.com/q/semester_8/power_plant_design/ror-vs-pror site: BCT Engineering --- # ROR versus PROR hydropower plants Power Plant Design · Chapter 3: Hydro Power Plant Design - Asked in: 2070 Magh, 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/ror-vs-pror - Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-3 ## Question Compare the components, operation and characteristics of run of river (ROR) type hydropower plant with pondage run of river (PROR). ## Short answer ROR: no storage, base-load, output follows river flow, lower cost. PROR: daily pondage, peaking operation, higher installed capacity, better load following, extra pond and surge tank, but hydro-peaking and small submergence impacts. Both share weir, intake, desander, headrace, penstock, powerhouse, tailrace. ## Answer A **run-of-river (ROR)** plant uses the river flow as it comes, with no storage. A **pondage run-of-river (PROR)** plant adds a small pond that stores water for a few hours so the plant can follow the daily load and give more power at peak time. | Aspect | ROR | PROR | |---|---|---| | Storage | None (only forebay) | Daily pondage, a few hours of storage | | Headworks | Low weir | Weir or slightly higher dam to create pond | | Extra component | — | Pondage with flushing arrangement | | Operation | Base load; output follows river flow | Peaking; stores off-peak water, generates more at peak | | Dry-season output | Low, nearly constant | Same energy, but concentrated into peak hours | | Installed capacity | Based on design flow (e.g. $Q_{45}$) | Can be higher than ROR for same river | | Load following | Poor | Good, within the pond volume | | Cost | Lowest | Higher (pond, larger dam, gates) | | Environmental impact | Least; dewatered stretch only | Adds small submergence and hydro-peaking downstream | | Sediment | Passes through after desander | Pond traps sediment, needs flushing | | Value to grid | Energy only | Energy plus peaking capacity | #### Components Both have: weir/dam, intake, gravel trap, desander, headrace, forebay or surge tank, penstock, powerhouse, tailrace and switchyard. PROR adds the **pondage** (and its spillway and flushing gates) and usually has a pressure tunnel with surge tank. #### Operation and characteristics - **ROR:** turbine discharge equals river inflow minus riparian release; in the wet season it runs at full load and spills the excess, in the dry season it runs at part load. - **PROR:** during the night the pond fills; in the 4–6 peak hours the plant runs at full load using inflow plus stored water. Total daily energy is about the same as ROR, but its value is higher because peak energy is scarce in Nepal. - Examples: many small IPP plants in Nepal are ROR; Kaligandaki "A" and Middle Marsyangdi are PROR. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the key difference between ROR and PROR? A. ROR has seasonal storage; PROR has none B. PROR has a small daily pondage; ROR has no storage C. Both have large reservoirs D. PROR has no weir Answer: B. PROR adds a pond storing water for a few hours; ROR uses the flow as it comes. (Key point: Storage difference) 2. How is a PROR operated compared with ROR? A. It runs at constant base load all day B. It shuts down during peak hours C. It fills the pond at night and runs at full load for 4-6 peak hours D. Its output follows river flow exactly Answer: C. PROR is a peaking plant using inflow plus stored water in peak hours; ROR output follows river flow. (Key point: Operation) 3. How does total daily energy of PROR compare with ROR for the same river? A. Much greater because storage creates water B. Much less because of evaporation C. Zero in the dry season D. About the same, but more valuable since it is peak energy Answer: D. The pond only shifts energy into peak hours; it does not create extra water. (Key point: Daily energy) 4. Which extra environmental impacts does PROR add? A. Small submergence and hydro-peaking downstream B. Seasonal flooding of large valleys C. Reduced riparian flow only D. None compared with ROR Answer: A. The pond floods a small area and releases cause daily flow fluctuation, plus sediment trapping. (Key point: Environmental) ## Related in Power Plant Design - [Daily pondage run-of-river components](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Adaily-pondage-ror-components) — Power Plant Design, chapter 3 - [Components of a run-of-river plant](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aror-components-functions) — Power Plant Design, chapter 3, asked 2× - [Schematic of a PROR hydropower plant](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Apror-schematic-components) — Power Plant Design, chapter 3, asked 2× - [Sketch of a medium head PROR plant](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Apror-medium-head-sketch) — Power Plant Design, chapter 3, asked 2× - [Daily pondage ROR with 150 m head](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Adaily-pondage-150m-head) — Power Plant Design, chapter 3 - [Hydropower plant components and functions](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Ahydropower-components-functions) — Power Plant Design, chapter 3, asked 2× ## Related in other subjects - [Working principle of RoR, PRoR and ST plants](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-pror-storage-working-principle) — Hydropower Engineering, chapter 2 - [RoR and PRoR from hydrograph equation (Q40)](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-pror-hydrograph-equation-q40) — Hydropower Engineering, chapter 3 - [RoR pondage: capacity and pondage volume](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-pondage-capacity-load-factor-65) — Hydropower Engineering, chapter 3 - [RoR installed capacity without pondage and with peaking](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-min-flow-pondage-peaking-70m) — Hydropower Engineering, chapter 3