---
title: "RoR headworks arrangement and functional requirements"
subject: "Hydropower Engineering"
chapter: 5
key: "semester_7/hydropower_engineering:ror-headworks-arrangement-requirements"
source: https://www.bctengineer.com/q/semester_7/hydropower_engineering/ror-headworks-arrangement-requirements
site: BCT Engineering
---

# RoR headworks arrangement and functional requirements

Hydropower Engineering · Chapter 5: Headworks of Run-of- River (RoR) Plants

- Asked in: 2081 Bhadra, 3+2 marks; 2072 Chaitra, 6+6 marks; 2070 Ashad, 2+3 marks (asked 3 times)
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/hydropower_engineering/ror-headworks-arrangement-requirements
- Whole chapter: https://www.bctengineer.com/md/semester_7/hydropower_engineering/chapter-5

## Question

Sketch a diagram (plan and section) showing the general arrangement of the components of a typical ROR plant headworks. List/describe the functional requirements of the headworks of an ROR plant (including the general requirements for optimum function in sediment loaded rivers).

## Short answer

A typical RoR headworks has a diversion weir, undersluice, side intake with trash rack and gate, gravel trap, approach canal, settling basin, and fish ladder. Functional requirements include safe flood passage, reliable diversion, minimum sediment entry, trash control, stability, environmental flow, and easy operation. In sediment-laden rivers, the intake sill is raised, undersluice provides flushing velocity, and frequent flushing during floods is needed.

## Answer

#### General arrangement of a typical RoR headworks
```text
PLAN
    river flow ==============================>
        left bank wall
   +-------------------------------------------+
   |  intake  | undersluice | weir (spillway)    |
   | (side)   |  (gates)    | ||||||||||||||||| |
   +----+-----+-------------+--------------------+
        |  gravel trap
        v                         fish ladder
   approach canal --> settling basin --> headrace
```

```text
SECTION through weir, undersluice and intake
  pond level ~~~~~~~~~~~~~~~~~~~~~~~~~~
        _____      weir crest  ______
  intake|rack |gate          /      \  stilling basin
  sill  |_____|-> canal     /        \____ apron
 ///////////  undersluice /////////  river bed
   (sill 1.0-1.5 m above bed)   flushing gate
```

Main components:
- **Diversion weir / barrage** across the river to raise the water level for the intake and pass floods over its crest.
- **Undersluice (scouring sluice)** at the intake side, with gates, to keep a flushing channel in front of the intake and to pass bed load.
- **Intake** (side intake with trash rack and gate) on the outer bank, with its sill above the undersluice level.
- **Gravel trap** and **approach canal** leading to the **settling basin**.
- **Fish ladder**, river training works (guide bunds, flood walls), stilling basin and apron downstream of the weir.

#### Functional requirements of the headworks
1. **Safe passage of floods**: the structure must be stable against the design flood (usually 1 in 100 year) and pass it with a limited afflux.
2. **Reliable diversion**: divert the design discharge at all river stages, including low flow, with the intake always submerged.
3. **Minimum sediment entry**: bed load must be kept out by a high sill, undersluice and gravel trap, and suspended load limited by the settling basin.
4. **Trash and floating debris control**: trash rack, trash boom and log deflector.
5. **Stability and safety**: weir safe against sliding, overturning and uplift; scour protected by cut-offs, aprons and a stilling basin.
6. **Environmental flow and fish passage** as per law; minimum release downstream.
7. **Easy operation and maintenance** with small head loss in the intake.

#### In rivers carrying a high sediment load
- Place the intake at the outer bend, with the sill at least 1.0-1.5 m above the undersluice crest.
- Make the undersluice large enough to give a flushing velocity that carries the boulders and gravel.
- Provide a gravel trap and a settling basin with efficient flushing; allow frequent flushing of the pond in floods.
- Use a flood-operation rule: close the intake during the high sediment-laden flood.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is the purpose of the undersluice?
   A. Release the environmental flow only
   B. Pass fish upstream
   C. Keep a flushing channel in front of the intake and pass bed load
   D. Dissipate energy below the weir
   Answer: C. The gated undersluice scours the approach so bed load is carried past the intake. (Key point: Undersluice role)

2. How high is the intake sill set above the undersluice crest in sediment-laden rivers?
   A. At least 1.0-1.5 m
   B. About 0.1 m
   C. About 5 m
   D. Level with the undersluice
   Answer: A. A raised sill stops bed load from entering the intake. (Key point: Intake sill level)

3. What flood is the headworks usually designed to pass?
   A. 1 in 2 year flood
   B. 1 in 100 year flood
   C. Mean annual flood
   D. 1 in 5 year flood
   Answer: B. Stability and flood passage are checked for the 100-year flood. (Key point: Design flood)

4. Where is the intake placed in a sediment-laden river?
   A. At the inner bend
   B. Directly at the weir centre
   C. Downstream of the stilling basin
   D. At the outer bend
   Answer: D. At the outer bend secondary currents move bed load away from the intake. (Key point: Intake location in bend)

## Related in Hydropower Engineering

- [General requirements of functional RoR headworks](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-headworks-requirements-only) — Hydropower Engineering, chapter 5, asked 2×
- [RoR headworks sketch; intake importance and location](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-headworks-arrangement-intake-location) — Hydropower Engineering, chapter 5
- [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×

## Related in other subjects

- [Functional block diagram of excitation control](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Aexcitation-control-block-diagram) — Power Plant Equipment, chapter 3
- [Combined plant components and T-s diagram](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Acombined-components-ts) — Power Plant Equipment, chapter 8, asked 4×
- [Components and layout of diversion headworks](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Aheadworks-components-layout) — Irrigation and Drainage Engineering, chapter 5, asked 2×
- [Headworks sketch, regulator section, protection works](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Aheadworks-sketch-regulator-section-dissipators) — Irrigation and Drainage Engineering, chapter 7