--- title: "Development stages and PRoR working principle" subject: "Hydropower Engineering" chapter: 2 key: "semester_7/hydropower_engineering:stages-pror-working-arrangement" source: https://www.bctengineer.com/q/semester_7/hydropower_engineering/stages-pror-working-arrangement site: BCT Engineering --- # Development stages and PRoR working principle Hydropower Engineering · Chapter 2: Planning of Hydropower Projects - Asked in: 2072 Kartik, 2+3+3 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/hydropower_engineering/stages-pror-working-arrangement - Whole chapter: https://www.bctengineer.com/md/semester_7/hydropower_engineering/chapter-2 ## Question What are the different stages of hydropower development? Explain the working principle of a peaking run-of-river plant and show the general arrangement of components with neat sketches. ## Short answer A PRoR plant has a weir with a small pond storing river flow for hours. In dry season, off-peak water is stored; peak hours stored water plus inflow run turbines at full capacity. In wet season it acts as RoR. Components: weir, intake, gravel trap, pond, desander, headrace tunnel, surge tank, penstock, powerhouse, tailrace. ## Answer #### Stages of hydropower development 1. Reconnaissance study 2. Pre-feasibility study 3. Feasibility study 4. Detailed engineering design and tender 5. Construction and commissioning 6. Operation and maintenance #### Working principle of a peaking run-of-river (PRoR) plant A PRoR plant has a weir plus a small reservoir (pond) at the headworks that can store the river flow for several hours. In the dry season the river flow is small. During the off-peak hours the turbines run at low load or stop, and the water is stored in the pond. In peak hours (usually 4-6 hours in the morning and evening) the stored water plus the inflow runs the turbines at full load. In the wet season, when flow is large, it behaves as an ordinary RoR plant. So the installed capacity is larger than for a pure RoR plant, and the energy has a higher value because it is supplied at peak time. Examples are Kaligandaki A and Upper Tamakoshi. #### General arrangement of components ```text River --> Weir + Undersluice --> Intake --> Gravel trap | | Pond (daily) Desander | Headrace tunnel | Surge tank | Penstock | Powerhouse --> Tailrace --> River ``` ```text Section FSL ~~~~~|weir intake====tunnel====(ST) MDDL ~~~~|pond \ penstock \__PH ``` Fluctuating pond level between FSL and MDDL gives the daily storage. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How does a peaking run-of-river plant operate in the dry season? A. It runs at full load all day B. It stores water in the pond at off-peak hours and runs at full load for a few peak hours C. It stops generation for the whole season D. It pumps water uphill at night Answer: B. The pond holds several hours of flow, which is used with the inflow at peak time. (Key point: PRoR principle) 2. How does a PRoR plant behave in the wet season? A. As a pumped storage plant B. It is shut down for floods C. It behaves as an ordinary RoR plant D. It uses a large seasonal reservoir Answer: C. With large flows the pond is not needed and the plant runs like a RoR plant. (Key point: Wet season behaviour) 3. Why is the installed capacity of a PRoR plant larger than for a pure RoR plant with the same river? A. Because it has a bigger weir height only B. Because the head is larger C. Because it uses less water D. Because stored water allows high output during the short peak hours Answer: D. Peaking use for 4-6 hours needs a larger capacity, and the peak energy has a higher value. (Key point: Installed capacity) 4. What gives the daily storage in a PRoR plant? A. Fluctuation of the pond level between FSL and MDDL B. The surge tank C. The tailrace pool D. The desander Answer: A. Pond drawdown between FSL and MDDL supplies the extra peak flow. (Key point: Daily storage) ## Related in Hydropower Engineering - [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 - [Stages of hydropower development cycle](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Adev-cycle-stages) — 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 - [Powerhouse general arrangement and dimensions](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Apowerhouse-arrangement-and-dimensions) — Hydropower Engineering, chapter 8, asked 3× - [RoR capacity, peaking capacity and benefit](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-three-sets-peaking-benefit) — Hydropower Engineering, chapter 3 - [RoR headworks arrangement and functional requirements](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-headworks-arrangement-requirements) — Hydropower Engineering, chapter 5, asked 3× ## Related in other subjects - [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× - [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 - [ROR versus PROR hydropower plants](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aror-vs-pror) — Power Plant Design, chapter 3