---
title: "Formation of an artesian well"
subject: "Engineering Geology II"
chapter: 3
key: "semester_4/engineering_geology_ii:artesian-formation"
source: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/artesian-formation
site: BCT Engineering
---

# Formation of an artesian well

Engineering Geology II · Chapter 3: Hydrogeology

- Asked in: 2075 Baisakh, 1 marks
- Video: [Artesian Well Flowing and Non Flowing - Tunnel Investigation and Ground Water Control](https://www.youtube.com/watch?v=KfRDlaF2etE) — Ekeeda
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/artesian-formation
- Whole chapter: https://www.bctengineer.com/md/semester_4/engineering_geology_ii/chapter-3

## Question

How is an artesian well (aquifer) formed?

## Short answer

An artesian well is formed by a confined aquifer: a permeable stratum between impervious beds tilted so recharge area is at higher elevation. Water under pressure rises in a well; if piezometric surface is above ground, it flows freely.

## Answer

An **artesian well** is formed when a permeable aquifer is confined between two impermeable beds and tilted so that its recharge area lies at a higher level than the well.

Conditions:
1. Inclined or synclinal (basin-shaped) permeable bed such as sandstone or sand.
2. Impermeable beds (clay, shale) above and below.
3. Outcrop of the aquifer at higher elevation where rain or river water enters (recharge).
4. Water flows down-dip and gets pressure from the weight of water in the higher part.

When a well is drilled through the upper confining bed, water rises above the aquifer top because of the pressure. If the piezometric surface is above the ground level, water flows out freely without pumping.

```text
 recharge area (outcrop)       flowing well
 high ground                       |  ^ ^
   ___.........piezometric surface.|..
  /   ___________clay_____________ | __ ground
 /   ===========sand aquifer======|====
/    ___________clay______________
```

## Check yourself

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

1. Which setting forms an artesian aquifer?
   A. A permeable bed confined between impermeable beds, tilted or synclinal, with its outcrop at higher ground
   B. A horizontal sand layer open to the surface with no confining beds
   C. A granite mass with no joints
   D. An aquifer lying above the water table with no clay cover
   Answer: A. Confinement by clay or shale above and below plus a higher recharge area gives the pressure. (Key point: Geological setting)

2. What gives water in an artesian aquifer its pressure?
   A. Pumping at the well
   B. The weight of water in the higher recharge part of the inclined aquifer
   C. Evaporation at the surface
   D. Heating of the rock
   Answer: B. Water entering at the higher outcrop flows down-dip and is pressurised by the water column above. (Key point: Source of pressure)

3. When does an artesian well flow freely without pumping?
   A. When the piezometric surface is below the aquifer top
   B. When the aquifer is unconfined
   C. When the piezometric surface is above the ground level
   D. When the well is drilled in the recharge area
   Answer: C. If the pressure head reaches above the ground, water overflows at the surface. (Key point: Flowing well)

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