---
title: "Types of spillway gates"
subject: "Hydro Power"
chapter: 6
key: "semester_6/hydro_power:spillway-gate-types"
source: https://www.bctengineer.com/q/semester_6/hydro_power/spillway-gate-types
site: BCT Engineering
---

# Types of spillway gates

Hydro Power · Chapter 6: Spillways

- Asked in: 2079 Chaitra, 6 marks; 2070 Bhadra, 6 marks (asked 2 times)
- Video: [How Different Spillway Gates Work](https://www.youtube.com/watch?v=Ry_3icwd68o) — Practical Engineering
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/hydro_power/spillway-gate-types
- Whole chapter: https://www.bctengineer.com/md/semester_6/hydro_power/chapter-6

## Question

Explain different types of gates to be provided for controlling the excess flow of water through the spillway.

## Short answer

Spillway gates control flood release. Main types: vertical lift gates (plain sliding, fixed-wheel, Stoney) lifted by hoists; radial (Tainter) gates with curved skin plate on trunnion pins, most common for large spans; drum gates hinged upstream, raised by water pressure; sector gates hinged downstream; flash boards and stop logs for temporary control; rolling gates; and flap/fuse gates that operate automatically. Selection depends on span, head, cost, debris, and power availability.

## Answer

**Spillway gates** are movable barriers on the spillway crest that hold water above the crest level during normal times (increasing storage) and are opened to release floods in a controlled way.

#### 1. Vertical lift gates
- **Plain sliding gates:** steel plates sliding in grooves; large friction, so used for small openings.
- **Fixed-wheel (roller) gates:** steel gates on wheels running on rails in piers; less friction, common for medium openings.
- **Stoney gates:** run on a free train of rollers between gate and pier, further reducing friction for large gates.
Lifted by hoists or gantry cranes; need tall piers and a hoist bridge.

#### 2. Radial (Tainter) gates
- Curved skin plate (part of a cylinder) supported by radial arms on trunnion pins in the piers.
- Water pressure passes through the pin, so lifting force is small; most common for large spillways.

#### 3. Drum gates
- Hollow segment of a cylinder hinged at the upstream edge, lying in a recess in the crest; raised and lowered by admitting water into the chamber below. Automatic operation; suits long crests.

#### 4. Sector gates
- Like a drum gate but hinged on the downstream side; rotates into a recess in the crest using reservoir pressure.

#### 5. Flash boards and stop logs
- **Flash boards:** temporary timber boards (0.5–1.2 m) on the crest, held by pins designed to fail during floods.
- **Stop logs:** horizontal beams placed in grooves between piers, removed by crane; used for maintenance or minor control.

#### 6. Rolling (roller) gates
- Large horizontal steel cylinder rolled up inclined racks in piers; spans long openings.

#### 7. Flap gates and automatic (fuse) gates
- **Flap gates:** hinged at the bottom; tilt down when water rises.
- **Fuse gates / fuse plugs:** units designed to tip over at a set flood level.

```text
 Vertical lift        Radial (Tainter)
   |hoist|              trunnion
   ||   ||               o
 ~~||===||~~         ~~~/|
   ||   ||          skin/ | arms
 __||___||__        ___(  |___
   crest               crest
```

**Selection** depends on span and height of opening, head, cost, ease of operation, ice/debris, and availability of power for hoisting.

## Check yourself

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

1. Why is the lifting force small for a radial gate?
   A. Water pressure passes through the trunnion pin, so it creates no moment about it
   B. The gate floats on the water
   C. It uses a counterweight of concrete
   D. It has no skin plate
   Answer: A. Only the gate weight and friction are lifted. (Key point: Radial gate principle)

2. Stoney gates reduce friction by
   A. floating on the reservoir
   B. running on a free train of rollers between gate and pier
   C. hinging at the bottom
   D. rotating on trunnions
   Answer: B. Rollers reduce friction for large gates. (Key point: Stoney gate)

3. A drum gate is operated by
   A. a gantry crane
   B. pins failing in a flood
   C. admitting water into the chamber below it
   D. removing beams with a crane
   Answer: C. Raised and lowered by water in the chamber. (Key point: Drum gate)

4. Flash boards are
   A. steel cylinders rolled on racks
   B. hinged gates raised by cables
   C. beams removed from grooves between piers
   D. temporary timber boards on the crest held by pins designed to fail in floods
   Answer: D. Stop logs are the grooved beams; flash boards fail intentionally. (Key point: Flash boards)

## Related in Hydro Power

- [Spillway gates and radial gate](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aspillway-gates-radial-gate) — Hydro Power, chapter 6
- [Spillway function, vertical and radial gates](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aspillway-function-vertical-radial-gate) — Hydro Power, chapter 6
- [Discharge over overflow spillway](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aoverflow-spillway-discharge) — Hydro Power, chapter 6
- [Water hammer in elastic cast-iron pipe](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Awater-hammer-cast-iron-pipe) — Hydro Power, chapter 1
- [Laminar/turbulent flow and friction factor](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Alaminar-turbulent-friction-factor) — Hydro Power, chapter 1

## Related in other subjects

- [Types of spillway crest gates](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aspillway-crest-gate-types) — Hydropower Engineering, chapter 4, asked 2×
- [Purposes of spillway; types of gates](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aspillway-purposes-and-gate-types) — Hydropower Engineering, chapter 4
- [Discharge through chute spillway ogee crest](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aspillway-chute-discharge-ogee-250m) — Hydropower Engineering, chapter 4
- [Reservoir routing through spillway, 6-hr inflow](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Areservoir-routing-spillway-6hr) — Engineering Hydrology, chapter 7