---
title: "Short note: culverts"
subject: "Transportation Engineering I"
chapter: 4
key: "semester_6/transportation_engineering_i:culverts-note"
source: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/culverts-note
site: BCT Engineering
---

# Short note: culverts

Transportation Engineering I · Chapter 4: Highway Drainage

- Asked in: 2068 Magh (old course), 4 marks; 2063 Kartik (old course), 4 marks (asked 2 times)
- Video: [What Is a Culvert?](https://www.youtube.com/watch?v=15XJDmawbYU) — Practical Engineering
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/culverts-note
- Whole chapter: https://www.bctengineer.com/md/semester_6/transportation_engineering_i/chapter-4

## Question

Write a short note on culverts.

## Short answer

A culvert is a short cross-drainage structure of clear span up to about 6 m, carrying stream or drain water below the road. Main types are pipe, box, slab, and arch culverts. Design discharge is found by rational method or empirical formulas, with about 25-year return period.

## Answer

A **culvert** is a short cross-drainage structure with a clear span of up to about 6 m (IRC/NRS 2070) that carries a small stream or the water from side drains below the road embankment. Larger structures are called bridges.

#### Components
- **Waterway (barrel / opening)**, **abutments and piers**, **deck slab or arch**, **wing walls and return walls**, **foundation and bed protection (apron)**, **headwalls**, **parapet** and **wearing surface**.

#### Types
1. **Pipe culvert**: Hume (RCC) or steel pipes, single or in rows. Cheap and easy; for small discharge.
2. **Box culvert**: RCC rectangular cells; for larger discharge and weak soil.
3. **Slab culvert**: RCC slab on abutments; open waterway.
4. **Arch culvert**: stone or concrete arch; for hill roads.

```text
 road surface =====================
 ====deck slab=====================
 |abutment|    waterway   |abutment|
 |________|_______________|________|
          apron / bed protection
```

#### Location and design points
- Place along the natural stream line, at right angles to the road if possible.
- Provide a bed gradient of 0.5 to 2% to avoid silting and scour.
- Find the design discharge by the rational method or the Dickens or Ryves empirical formulas, with a return period of about 25 years for culverts (and a check for a higher flood).
- Provide the required minimum cover, inlet and outlet protection, and a free board.
- Culverts are spaced more closely on hill roads (every 100 to 250 m) to avoid long drain runs.

Culverts are generally cheaper and simpler than bridges, but they must be cleaned regularly to avoid blockage by debris.

## Check yourself

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

1. A culvert is:
   A. A longitudinal side drain
   B. A sub-surface drain
   C. Any bridge over 6 m
   D. A cross-drainage structure with clear span up to about 6 m
   Answer: D. Larger structures are called bridges. (Key point: Definition)

2. How should a culvert be located?
   A. Along the natural stream line, at right angles to the road if possible
   B. Anywhere convenient
   C. At a steep skew
   D. Away from the stream
   Answer: A. Locating along the natural stream line with minimum skew keeps flow smooth. (Key point: Location)

3. What gradient is provided to avoid silting and scour?
   A. 5 to 8%
   B. 0.5 to 2%
   C. 10 to 15%
   D. Zero
   Answer: B. A moderate gradient prevents silting and scour. (Key point: Design gradient)