---
title: "Hydropower intake sketch; minimizing head loss"
subject: "Hydropower Engineering"
chapter: 5
key: "semester_7/hydropower_engineering:hydropower-intake-sketch-minimise-headloss"
source: https://www.bctengineer.com/q/semester_7/hydropower_engineering/hydropower-intake-sketch-minimise-headloss
site: BCT Engineering
---

# Hydropower intake sketch; minimizing head loss

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

- Asked in: 2072 Chaitra, 3+1 marks
- Video: [COMPONENTS OF DIVERSION HEADWORK | ANIMATED VIDEO LECTURE | GATE | ASSISTANT ENGINEER | SUB ENGINEER](https://www.youtube.com/watch?v=oBisIdBDcLo) — Amaze Academy for Civil Engineering
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/hydropower_engineering/hydropower-intake-sketch-minimise-headloss
- Whole chapter: https://www.bctengineer.com/md/semester_7/hydropower_engineering/chapter-5

## Question

Draw a neat sketch of a hydropower intake, showing major components. How do you minimize head loss in the intake?

## Short answer

Major components are trash rack, gate, sill, hoist deck, bell-mouth transition and undersluice. Minimize loss by low rack velocity 0.6-1.0 m/s, streamlined bars, bell-mouth entrance, gradual transitions, few gate slots, smooth lining and large bend radius.

## Answer

#### Sketch of a hydropower intake (non-pressurized side intake of a RoR plant)
```text
PLAN
 river ==========================>
   weir |||||||| undersluice
   bank +----------------------+
        | rack    gate  bell   |--> gravel trap --> canal
        +----------------------+

SECTION
 pond ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  boom o  | trash rack | gate | hoist deck
          |###\        |      |
          |####\_______|______|=====> conduit
   sill (1.0-1.5 m above bed)   transition
 ///////////////////////////////////////// bed
```
Major components: trash boom, trash rack (inclined), intake sill, regulating gate with stop-log slot, hoist deck, bell-mouthed transition, flushing undersluice and the conduit to the gravel trap or settling basin.

#### Minimising head loss in the intake
Head loss reduces the net head and so the energy produced. It is reduced by:
- **Low velocity at the trash rack** (0.6-1.0 m/s) by providing a large rack area; the loss varies with $V^2$.
- **Streamlined bars** (rounded or tapered upstream edges, $\beta$ of 0.76-1.8 instead of 2.42), larger spacing, and regular raking to avoid clogging.
- **Bell-mouthed, rounded entrance** instead of a sharp-edged entry (loss coefficient 0.05-0.1 instead of 0.5).
- **Gradual transitions** (contraction or expansion not steeper than about 1:5) and smooth curved wing walls.
- **Few gate slots and piers**, and a fully open gate in operation.
- **Smooth lining**, short conduit and large bend radius; avoiding sharp bends at the entry.

## Check yourself

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

1. Why use low rack velocity?
   A. To admit more bed load
   B. Loss varies with V^2
   C. To raise the sill
   D. To avoid gates
   Answer: B. Providing a large rack area lowers V and the loss. (Key point: Rack velocity)

2. How does a bell-mouth help?
   A. Cuts the entry loss coefficient from 0.5 to 0.05-0.1
   B. Increases the loss
   C. Removes the need for a rack
   D. Makes the sill higher
   Answer: A. Rounded entry reduces contraction. (Key point: Entrance shape)

3. What is a good transition limit?
   A. 1:1
   B. Sudden step
   C. Contraction or expansion not steeper than about 1:5
   D. 90 degrees
   Answer: C. Gradual transitions avoid separation and loss. (Key point: Transitions)

## Related in Hydropower Engineering

- [Side intake sketch; trash rack loss](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aintake-side-sketch-trashrack-loss) — Hydropower Engineering, chapter 5
- [Types of hydropower plants by head, turbine, load](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Ahydropower-plant-types-classification) — Hydropower Engineering, chapter 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
- [Settling basin 60 m³/s, 0.15 mm, head 300 m](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Asettling-basin-60cumec-300m-015mm-turbulence) — Hydropower Engineering, chapter 5, asked 2×
- [What is an intake? Functions and sketch](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aintake-definition-functions-sketch) — Hydropower Engineering, chapter 5, asked 2×
- [Requirements of a good intake; types in Nepal](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aintake-requirements-types-nepal) — Hydropower Engineering, chapter 5

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