---
title: "Spring formation; infiltration gallery"
subject: "Water Supply Engineering"
chapter: 2
key: "semester_5/water_supply_engineering:springs-formation-infiltration-gallery"
source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/springs-formation-infiltration-gallery
site: BCT Engineering
---

# Spring formation; infiltration gallery

Water Supply Engineering · Chapter 2: Sources of Water

- Asked in: 2081 Bhadra, 1+3 marks
- Video: [Sources Of Water | Infiltration Well, Infiltration Gallery, Springs, Wells, Storage Reservoir etc.](https://www.youtube.com/watch?v=0BCBVBUGw0U) — Civil Engineering Education
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/water_supply_engineering/springs-formation-infiltration-gallery
- Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-2

## Question

Under what circumstances are springs formed? With the help of neat sketches, describe an infiltration gallery.

## Short answer

Springs form when the water table meets the surface or an impervious layer forces ground water out; types include depression, contact, fault, artesian, and fissure springs. An infiltration gallery is a horizontal perforated pipe laid below the water table along a river bank, surrounded by gravel and sand, collecting naturally filtered water to a sump.

## Answer

#### Formation of springs
A spring is a natural outflow of ground water at the ground surface. It forms when the water table meets the ground surface, or when ground water is forced out by an impervious layer. The main circumstances are:
1. **Depression spring:** the ground surface dips below the water table in a valley or hollow.
2. **Contact (gravity) spring:** an impervious layer below a pervious layer on a hill slope blocks the downward movement and water emerges at the contact.
3. **Fault spring:** a fault or fracture brings a confined aquifer in contact with the surface.
4. **Artesian spring:** confined water under pressure rises through a crack in the overlying impervious layer.
5. **Fissure or solution spring:** water comes out through joints and cavities in rock such as limestone.

```text
 Contact spring           Artesian spring
  ___________              ground
 / pervious  \___        ____  ____
/____________    \__ o  ====impervious====
 impervious  -----> spring   confined aquifer
```

#### Infiltration gallery
An infiltration gallery is a horizontal perforated pipe or porous conduit laid below the water table, usually along a river bank or in a water-bearing sand layer, which collects water by seepage and delivers it to a sump well.

```text
  river ~~~~~~~~~~~~~~~~
  ground ===========\===
       gravel+sand   \
   o  o  o  o  o  o  -> [Sump well]
   perforated pipe, 1 in 500 slope
   ------- impervious layer -------
```

- Trench 3 to 6 m deep, pipe diameter 0.3 to 0.9 m laid on a slight slope to the sump.
- Pipe surrounded by graded gravel and sand; the top is sealed with clay to stop surface pollution.
- Manholes are provided for cleaning.
- Water is naturally filtered, so it needs little treatment.

## Check yourself

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

1. A contact (gravity) spring forms when:
   A. A confined aquifer rises through a crack
   B. An impervious layer under a pervious layer on a slope blocks water so it emerges at the contact
   C. Ground dips below the water table
   D. Limestone dissolves
   Answer: B. Impervious layer blocks downward movement, so water emerges at the contact. (Key point: Contact spring)

2. An artesian spring is caused by:
   A. Surface runoff
   B. Fissures in limestone
   C. Depressions
   D. Confined water under pressure rising through a crack in the cover
   Answer: D. Pressure in a confined aquifer pushes water up through a crack. (Key point: Artesian spring)

3. The infiltration gallery pipe is laid:
   A. Vertically
   B. With slight slope toward a sump well
   C. Flat above water table
   D. Without perforations
   Answer: B. A slight slope such as 1 in 500 carries water to the sump well. (Key point: Gallery slope)

## Related in Water Supply Engineering

- [Infiltration gallery construction](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ainfiltration-gallery) — Water Supply Engineering, chapter 2, asked 4×
- [Population from spring yield of 5 L/s](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Apop-s71) — Water Supply Engineering, chapter 3
- [Intake site factors; spring intake](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aspring-intake-site-factors) — Water Supply Engineering, chapter 5
- [Factors in constructing a spring intake](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aspring-intake-factors-constructing) — Water Supply Engineering, chapter 5

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