---
title: "Spillways, gates and types of spillways"
subject: "Hydro Power"
chapter: 6
key: "semester_6/hydro_power:spillways-and-gates"
source: https://www.bctengineer.com/q/semester_6/hydro_power/spillways-and-gates
site: BCT Engineering
---

# Spillways, gates and types of spillways

Hydro Power · Chapter 6: Spillways

- Asked in: 2080 Chaitra, 2+4 marks
- Video: [#spillway SPILLWAYS: TYPES OF SPILLWAYS & ITS CLASSIFICATION #spillway #civilengineering](https://www.youtube.com/watch?v=1w-MmF0jujY) — 𝐁𝐥𝐨𝐨𝐦 𝐰𝐢𝐭𝐡 𝐀𝐧𝐚𝐦𝐢𝐤𝐚
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/hydro_power/spillways-and-gates
- Whole chapter: https://www.bctengineer.com/md/semester_6/hydro_power/chapter-6

## Question

What are Spillways and gates? What are the various types of spillways used in Hydropower projects?

## Short answer

Spillways safely release surplus flood water to prevent dam overtopping. Gates are movable steel barriers on the crest to control outflow and increase storage. Common spillway types include ogee, chute, side channel, shaft (morning glory), siphon, tunnel, labyrinth, stepped, and free overfall.

## Answer

#### Spillways
A **spillway** is a structure built with a dam to release surplus flood water from the reservoir safely to the downstream river when the reservoir is full, protecting the dam from overtopping and failure.

#### Gates
**Spillway gates** are movable steel barriers placed on the spillway crest between piers. They store water above the crest during normal operation (increasing storage and head) and are opened during floods to control the outflow. Common types: vertical lift (fixed-wheel, Stoney), radial (Tainter), drum, sector, rolling gates, flash boards and stop logs.

#### Types of spillways used in hydropower projects
1. **Free overfall (straight drop) spillway:** water drops freely over a thin crest; used for low arch or thin dams on hard rock, with a plunge pool or apron below.
2. **Ogee (overflow) spillway:** crest shaped to the lower nappe of a sharp-crested weir; high discharge coefficient ($C \approx 2.2$); most common on concrete gravity dams and barrages.
3. **Chute (trough) spillway:** short crest followed by a steep lined open channel to the river; used with earth and rockfill dams; placed on an abutment or saddle.
4. **Side channel spillway:** crest along the side of a channel; water spills laterally and turns 90° into a chute or tunnel; useful in narrow valleys where a long crest is needed.
5. **Shaft (morning glory) spillway:** water enters a funnel-shaped circular crest, falls down a vertical shaft and exits through a horizontal tunnel (often the diversion tunnel). Suitable where there is no room for other types.
6. **Siphon spillway:** inverted U-shaped closed conduit; once primed it gives large discharge for small rise in water level, keeping the reservoir level nearly constant.
7. **Tunnel (conduit) spillway:** closed tunnel through the abutment or a conduit through the dam carries the flood.
8. **Labyrinth spillway:** zigzag crest in plan gives a long crest in a narrow width.
9. **Stepped spillway:** steps on the downstream face dissipate energy along the chute.

```text
  Ogee         Chute            Shaft
 ~~__        ~~|--\           ~~\   /~~
   / \_          \  \            | |
  |    \__        \__\___        | |____
  |_______\~~      stilling      |______ tunnel
```

## Check yourself

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

1. Spillway gates are used to
   A. store water above the crest normally and release floods in a controlled way
   B. lower the dam height
   C. filter sediment
   D. prevent all flow
   Answer: A. They increase storage and head and are opened in floods. (Key point: Gate function)

2. A shaft (morning glory) spillway consists of
   A. a zigzag crest
   B. a funnel crest, vertical shaft and horizontal tunnel
   C. an inverted U
   D. a stepped face
   Answer: B. Water enters circular crest and exits via a tunnel. (Key point: Shaft)

3. A labyrinth spillway is used to
   A. dissipate energy on steps
   B. pass flow through a tunnel
   C. get a long crest within a narrow width
   D. prime a siphon
   Answer: C. The zigzag crest in plan lengthens it. (Key point: Labyrinth)

4. A free overfall spillway suits
   A. large earth dams
   B. weak soil
   C. barrages in flat plains
   D. low arch or thin dams on hard rock with a plunge pool
   Answer: D. Water drops freely from a thin crest. (Key point: Free overfall)

## Related in Hydro Power

- [Spillway types suitable for Nepalese rivers](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aspillway-types-nepal) — Hydro Power, chapter 6
- [Types of intakes and their suitability](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aintake-types) — Hydro Power, chapter 5, asked 2×
- [Flow duration curve and planning parameters](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Afdc-planning-parameters) — Hydro Power, chapter 3
- [Pre-feasibility versus feasibility studies](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aprefeasibility-vs-feasibility) — Hydro Power, chapter 3
- [Cavitation erosion and energy dissipators](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Acavitation-erosion-energy-dissipators) — Hydro Power, chapter 6

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- [Equipment used in hydropower construction](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Ahydropower-equipment) — Construction Management, chapter 4
- [Purpose and types of spillways](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aspillway-purpose-types-explain-one) — Hydropower Engineering, chapter 4, asked 4×