---
title: "Groynes and their types"
subject: "Irrigation and Drainage Engineering"
chapter: 6
key: "semester_6/irrigation_and_drainage_engineering:groynes-types"
source: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/groynes-types
site: BCT Engineering
---

# Groynes and their types

Irrigation and Drainage Engineering · Chapter 6: River Training Works

- Asked in: 2070 Chaitra (old course), 8 marks
- Video: [Groynes and their Classifications | Attracting, Repelling, Deflecting and Sediment Groynes](https://www.youtube.com/watch?v=qWCm5ItTf7g) — Let's GROW!
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/groynes-types
- Whole chapter: https://www.bctengineer.com/md/semester_6/irrigation_and_drainage_engineering/chapter-6

## Question

Define groynes and explain different types of groynes.

## Answer

A **groyne** (or **spur**) is a structure built out from the river bank, roughly at right angles or inclined to the current, to deflect the flow away from the bank, reduce velocity near the bank and induce silting. The root is anchored in the bank and the head projects into the stream.

#### Types of groynes
**1. According to the effect on the current (inclination)**
- **Repelling groyne:** inclined upstream (100 to 120° with the bank). It pushes the current toward the middle, but the scour at the head is heavy.
- **Attracting groyne:** inclined downstream (60 to 70°). It attracts the current, and has little scour.
- **Deflecting or neutral groyne:** at right angles to the bank. The commonest type.

```text
 Repelling         Deflecting        Attracting
  \                 |                  /
   \ flow->          |                 /
 ---------        ---------        ---------
```

**2. According to permeability**
- **Impermeable groynes** are of earth, stone, concrete or gabion. They block the flow.
- **Permeable groynes** are of piles, bamboo or brushwood, or wire crates with stone. They let a slow flow pass, causing silt deposits, and have little scour; they suit sandy, low-velocity rivers.

**3. According to shape of the head**
- Straight groyne, **T-head** groyne and **hockey (curved) head** groyne. A T-head gives better protection and reduces scour at the nose.

**4. According to the height**
- **Submerged groynes** are overtopped in floods.
- **Non-submerged groynes** stand above HFL.

**5. According to the material**
- Earth with stone pitching, boulder or stone masonry, concrete block, gabion and bio-engineering types.

#### Design features
- Length limited to about 20 % of river width; spacing about 2 to 2.5 times the length on concave banks.
- Top width 3 to 6 m and top level at HFL plus a margin.
- Heads protected with pitching and a launching apron.

## Check yourself

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

1. What is a groyne?
   A. A dam across the river
   B. A weir with gates
   C. A structure projecting from the bank into the river to deflect flow away, reduce velocity near the bank and induce silting
   D. A canal outlet
   Answer: C. A groyne (spur) has its root in the bank and its head in the stream. (Key point: Groyne definition)

2. Which matches the inclination type to its angle and behaviour?
   A. Repelling: 100-120 degrees upstream, heavy scour at head; Attracting: 60-70 degrees downstream, little scour
   B. Neutral: 45 degrees
   C. Repelling: 60-70 degrees; Attracting: 100-120
   D. Attracting: heavy scour
   Answer: A. Repelling groynes point upstream and scour at the head; attracting ones point downstream with little scour. (Key point: Inclination types)

3. How do permeable groynes work?
   A. Increase scour
   B. Let slow flow pass, causing silt deposit with little scour; suit sandy low-velocity rivers
   C. Block flow completely
   D. Made only of concrete
   Answer: B. Piles, bamboo, brushwood or wire crates slow the flow and encourage deposition. (Key point: Permeability)

4. What is the benefit of a T-head groyne?
   A. Cheaper root
   B. Attracts the current
   C. Better protection and reduced scour at the nose
   D. Greater scour at the head
   Answer: C. T-head and hockey heads reduce nose scour and protect downstream. (Key point: Head shape)

5. Typical design features of groynes?
   A. No apron needed
   B. Length up to about 20% of river width, spacing 2-2.5 L on concave banks, pitched heads with launching apron
   C. Length 100% of width
   D. Spacing 0.1 L
   Answer: B. Length is limited to avoid choking, and heads need pitching and an apron. (Key point: Design limits)