---
title: "Objectives of RT works and spur spacing"
subject: "Irrigation and Drainage Engineering"
chapter: 6
key: "semester_6/irrigation_and_drainage_engineering:river-training-objectives-spur-spacing"
source: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/river-training-objectives-spur-spacing
site: BCT Engineering
---

# Objectives of RT works and spur spacing

Irrigation and Drainage Engineering · Chapter 6: River Training Works

- Asked in: 2071 Bhadra, 1+2+3+2 marks
- 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/river-training-objectives-spur-spacing
- Whole chapter: https://www.bctengineer.com/md/semester_6/irrigation_and_drainage_engineering/chapter-6

## Question

What is meant by river training works and what are the different objectives served by it. What are the underlying principles behind the determination of spur spacing. Draw L and X-section of a typical spur.

## Short answer

River training works are structures built along a river to guide flow, stabilize the course, and protect banks from erosion. Objectives include preventing outflanking of structures, providing axial approach flow, controlling silt entry, and maintaining a channel for navigation. Spur spacing depends on the flow's expansion angle (~10–15°); it must be close enough that the eroding current does not reach the bank. Typical spacing is 2–2.5 times length on concave banks, 3–4 times on straight ones, with smaller values for sharp curves, high velocity, or weak soils, and length should not exceed 0.2 of the river width.

## Answer

#### River training works (1 mark)
**River training works** are structures built on or along a river to guide the flow, control the river course, and protect banks and structures from erosion and floods.

#### Objectives (2 marks)
1. Prevent the river from outflanking a bridge, barrage or town, and hold it in a stable course.
2. Protect banks from erosion and the land from flooding.
3. Provide an axial, uniform approach flow to structures, and control silt entry.
4. Maintain a good channel for navigation or water supply.

#### Principles behind spur spacing (3 marks)
The spacing must be such that the eroding current cannot reach the bank between two spurs.
1. The flow leaving the head of a spur spreads out at a small angle (about 10° to 15° with the spur line). The next spur must lie inside the protected zone, so spacing is limited by this expansion angle.
2. Spacing is related to spur length $L$: about $2$ to $2.5L$ on a concave bank, $3$ to $4L$ on a straight reach and larger on a convex bank.
3. Spacing becomes smaller for: sharper curvature, higher velocity, weaker bank soil, and greater deflection.
4. The area between spurs should silt up quickly. A very large spacing leaves the bank unprotected; a very small one wastes money.
5. The river width and spur length should not choke the channel: $L \le 0.2W_{river}$.

#### Longitudinal and cross-section of a spur (2 marks)
```text
 Longitudinal section (along spur axis)
  top level HFL+1 m ________ nose
  bank  ---------/        \
      root       slope 1:1 ... 3:1 at nose
  bed ---------------------------- launching apron

 Cross-section
        3-6 m
      _________
     /         \  side slopes 2:1 (3:1 at head)
 ---/ pitching   \---
 bed__ filter ____ apron
```
Top width is 3 to 6 m, top level HFL $+$ 1 m (sloping down toward the head), and the head is pitched with stone and an apron.

## Check yourself

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

1. What are river training works?
   A. Structures that guide the flow, control the river course and protect banks and structures
   B. Canals for irrigation
   C. Drainage pipes
   D. Reservoir dams only
   Answer: A. They guide flow, hold a stable course and protect against erosion and floods. (Key point: Definition)

2. What basic principle governs spur spacing?
   A. Spacing is independent of bank conditions
   B. The eroding current spreading out from a spur head (about 10-15 degrees) must not reach the bank before the next spur
   C. Spacing equals river width
   D. Spurs are spaced as far apart as possible
   Answer: B. The next spur must lie within the protected zone behind the previous one, limited by the expansion angle. (Key point: Spacing principle)

3. In which case should spacing be smaller?
   A. Sharper curvature, higher velocity, weaker bank soil
   B. Straight reach with strong soil
   C. Low velocity
   D. Convex bank
   Answer: A. More aggressive conditions require closer spurs to keep the bank protected. (Key point: Factors reducing spacing)

4. Typical spacing relative to spur length L?
   A. 2-2.5L on concave bank, 3-4L on straight reach
   B. 0.5L on straight reach
   C. 20L on concave bank
   D. Equal on all banks
   Answer: A. Spacing is larger on straight reaches and convex banks than on concave ones. (Key point: Spacing versus length)

5. Typical spur cross-section?
   A. No pitching
   B. Top below bed level
   C. Top width 0.5 m, slope 1:5
   D. Top width 3-6 m, top at HFL + 1 m, side slopes 2:1 (3:1 at head), pitched head with apron
   Answer: D. The head is pitched and protected by a launching apron. (Key point: Spur section)

## Related in Irrigation and Drainage Engineering

- [Define RT works, objectives, purposes of spur](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Ariver-training-objectives-spur-purposes) — Irrigation and Drainage Engineering, chapter 6
- [Objectives of river training works](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Ariver-training-objectives-five) — Irrigation and Drainage Engineering, chapter 6
- [RT works for a bridge; launching apron](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Ariver-training-bridge-launching-apron) — Irrigation and Drainage Engineering, chapter 6
- [RT works, methods and guide bank components](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Ariver-training-guide-bank-components-62b) — Irrigation and Drainage Engineering, chapter 6
- [Methods of river training with sketches](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Ariver-training-methods-sketch) — Irrigation and Drainage Engineering, chapter 6, asked 6×
- [River training methods and types of spurs](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Ariver-training-methods-spurs-types) — Irrigation and Drainage Engineering, chapter 6

## Related in other subjects

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