---
title: "Intake and its functions"
subject: "Hydro Power"
chapter: 5
key: "semester_6/hydro_power:intake-functions"
source: https://www.bctengineer.com/q/semester_6/hydro_power/intake-functions
site: BCT Engineering
---

# Intake and its functions

Hydro Power · Chapter 5: Components of Hydropower System

- Asked in: 2082 Kartik, 1+3 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/hydro_power/intake-functions
- Whole chapter: https://www.bctengineer.com/md/semester_6/hydro_power/chapter-5

## Question

What is an intake? Write its functions.

## Short answer

An intake diverts design flow from the river into the water conductor, controlling flow with gates. Its functions include excluding floating debris and bed load via trash racks and sill, minimising head loss with smooth entry, preventing vortex air entry, and protecting against floods.

## Answer

An **intake** is the structure at the head of a water conductor system that diverts the required design discharge from a river or reservoir into the canal, tunnel or penstock leading to the powerhouse, while keeping out debris, ice and as much sediment as possible.

#### Functions of an intake
1. **Diversion of design flow:** draws the required discharge (design discharge plus flushing flow) into the water conductor at all river stages, including the lean (dry) season.
2. **Control of flow:** gates at the intake regulate the flow and can shut it off completely for maintenance of the waterway or during floods.
3. **Exclusion of floating debris:** trash racks stop logs, branches, leaves and ice from entering and damaging the turbines.
4. **Exclusion of bed load:** a raised sill, undersluice and gravel trap keep coarse sediment (gravel, boulders) out of the waterway.
5. **Minimising head loss:** a smooth bell-mouth entrance with low approach velocity (about 0.6–1.0 m/s through the racks) reduces entry losses.
6. **Prevention of vortex and air entry:** adequate submergence prevents vortices that would draw air into a pressure conduit.
7. **Flood protection:** limits the flow entering the waterway during floods so that the canal or tunnel is not overloaded; excess is spilled back to the river.

```text
 River --> [Trash rack] -> [Gate] -> [Gravel trap]
                                        |
                                        v
                         Headrace canal / tunnel
```

## Check yourself

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

1. An intake is:
   A. The structure that diverts the design discharge into the waterway while excluding debris and sediment
   B. The turbine inlet valve
   C. A tailwater pond
   D. A surge shaft
   Answer: A. It sits at the head of the conductor system. (Key point: Intake definition)

2. What does the trash rack do?
   A. Measures flow
   B. Removes dissolved salts
   C. Stops logs, leaves, boulders and ice from entering
   D. Increases head
   Answer: C. It protects turbines from floating debris. (Key point: Trash rack)

3. Which features keep coarse sediment out?
   A. Raised sill, undersluice and gravel trap
   B. Air vent
   C. Gate only
   D. Bell mouth only
   Answer: A. A raised sill and undersluice keep bed load away from the opening. (Key point: Bed load exclusion)

4. Adequate submergence at the intake prevents:
   A. Sediment settling
   B. Gate corrosion
   C. Vortices that draw air into a pressure conduit
   D. Floods
   Answer: C. Low submergence causes air-entraining vortices. (Key point: Vortex prevention)

## Related in other subjects

- [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×
- [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