---
title: "What is an intake? Functions and sketch"
subject: "Hydropower Engineering"
chapter: 5
key: "semester_7/hydropower_engineering:intake-definition-functions-sketch"
source: https://www.bctengineer.com/q/semester_7/hydropower_engineering/intake-definition-functions-sketch
site: BCT Engineering
---

# What is an intake? Functions and sketch

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

- Asked in: 2081 Baishakh, 4 marks; 2075 Chaitra, 1+2 marks (asked 2 times)
- Video: [INTAKE STRUCTURES  : Intake Functions &Understanding Types](https://www.youtube.com/watch?v=NaMFbG5Amz4) — OPengineer
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/hydropower_engineering/intake-definition-functions-sketch
- Whole chapter: https://www.bctengineer.com/md/semester_7/hydropower_engineering/chapter-5

## Question

What do you mean by an intake? Write down its functions and sketch a generalized intake structure for a RoR diversion project.

## Short answer

An intake is the structure that withdraws design discharge from the river into the conveyance system. Its functions: divert required flow, control with gate, exclude bed load and trash via sill and rack, limit sediment entry, and provide smooth transition. The sill is 1.0-1.5 m above the undersluice bed to prevent bed load entry.

## Answer

#### Definition
An **intake** is the structure at the head of the water conductor system that withdraws the design discharge from the river (or reservoir) and admits it into the canal, tunnel or pipe in a controlled way.

#### Functions
- Diverts the required discharge into the conveyance system at all river levels.
- Controls the flow with a gate; shuts it off for inspection and during floods.
- Excludes the bed load and the floating trash and debris through the sill, trash rack and trash boom.
- Limits the entry of sediment and passes it to the gravel trap and settling basin.
- Provides a smooth, low-loss transition and prevents air entry and vortices.

#### Sketch of a generalized RoR intake
```text
PLAN
 river ===>  ||||||||||| weir
                 __________________________
 undersluice =|  trash rack  gate   |==> approach
 (flushing)   |_____________________|    canal

SECTION
  pond ~~~~~~~~~~~~~~~~~~
        |    | rack   ____ gate
        |    |##   \ |    |
  sill  |____|##____\|____|=====> canal
  ///////////////// river bed (undersluice lower)
```
The sill of the intake is kept 1.0-1.5 m above the bed of the undersluice so that bed load cannot enter; the opening is sized so that the velocity at the trash rack is about 0.8-1.0 m/s.

## Check yourself

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

1. What is an intake?
   A. A basin that removes silt
   B. A structure that dissipates spillway energy
   C. A channel that returns water to the river
   D. Structure at the head of the water conductor that withdraws the design discharge in a controlled way
   Answer: D. It admits the design discharge from river or reservoir into the canal, tunnel or pipe. (Key point: Intake definition)

2. Why is the intake sill kept 1.0-1.5 m above the undersluice bed?
   A. So bed load cannot enter
   B. To increase head
   C. To reduce rack velocity
   D. To prevent vortices
   Answer: A. The raised sill excludes bed load. (Key point: Sill height)

3. What approximate velocity at the trash rack is used for sizing?
   A. 3-4 m/s
   B. 0.05 m/s
   C. 0.8-1.0 m/s
   D. 8-10 m/s
   Answer: C. Low rack velocity keeps head loss small and avoids pulling in debris. (Key point: Rack velocity)

## Related in Hydropower Engineering

- [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
- [Parts of pressurized and non-pressurized RoR intake](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aintake-parts-pressurized-nonpressurized-sketch) — Hydropower Engineering, chapter 5
- [Optimizing plant capacity of a RoR project](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-optimum-capacity-discussion) — Hydropower Engineering, chapter 3
- [Design of orifice type intake](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aintake-orifice-design-5cumec) — Hydropower Engineering, chapter 5
- [Control of bed load and floating debris at intake](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-intake-bedload-debris-control) — Hydropower Engineering, chapter 5
- [RoR layout: pressure tunnel and free surface](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-layout-pressure-tunnel-free-flow) — Hydropower Engineering, chapter 2

## Related in other subjects

- [Intake site selection for RoR plant](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aintake-site-selection-ror) — Hydro Power, chapter 5
- [Intake and its functions](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aintake-functions) — Hydro Power, chapter 5
- [Intake, its functions and site factors](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aintake-functions-site-factors) — Water Supply Engineering, chapter 5
- [Project financing; structures; capital structure steps](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Aproject-finance-define-structures-steps) — Project Engineering, chapter 6