---
title: "Earth dam flow type"
subject: "Soil Mechanics"
chapter: 7
key: "semester_4/soil_mechanics:earth-dam-confined-or-unconfined"
source: https://www.bctengineer.com/q/semester_4/soil_mechanics/earth-dam-confined-or-unconfined
site: BCT Engineering
---

# Earth dam flow type

Soil Mechanics · Chapter 7: Seepage through Soils

- Asked in: 2073 Magh, 1 marks
- Video: [Seepage though Earthen Dam || Soil Mechanics | Chapter 7 | Most important theory](https://www.youtube.com/watch?v=wmVYDaAoP7s) — Sudip Dhakal
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/soil_mechanics/earth-dam-confined-or-unconfined
- Whole chapter: https://www.bctengineer.com/md/semester_4/soil_mechanics/chapter-7

## Question

Is the flow through an earth dam confined flow or unconfined flow?

## Short answer

Flow through an earth dam is unconfined because the top flow line (phreatic line) is a free surface under atmospheric pressure whose position is not known in advance and must be located.

## Answer

The flow through the body of an earth dam is **unconfined flow**, because the top flow line (phreatic line) is a free surface under atmospheric pressure whose position is not known in advance and must be located.

## Check yourself

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

1. Flow through the body of an earth dam is:
   A. Confined
   B. Unconfined
   C. Turbulent only
   D. Artesian
   Answer: B. The top flow line is a free surface, so the flow is unconfined. (Key point: Type of flow)

2. Why is it unconfined?
   A. The phreatic line is a free surface at atmospheric pressure of unknown position
   B. The dam base is impervious
   C. The soil is anisotropic
   D. The head is zero
   Answer: A. The unknown free surface is what makes the flow unconfined. (Key point: Reason)

3. What must be done for an earth dam because of this?
   A. Ignore the top flow line
   B. Locate the phreatic line before completing the flow net
   C. Assume it is horizontal
   D. Use the Bligh method
   Answer: B. The phreatic line must be located first, then the flow net is completed below it. (Key point: Consequence)

## Related in Soil Mechanics

- [Confined and unconfined flow](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aconfined-unconfined-seepage-flow) — Soil Mechanics, chapter 7
- [Confined and unconfined aquifers](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aconfined-unconfined-aquifers-k) — Soil Mechanics, chapter 6
- [Earth dam flow net and discharge](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aearth-dam-flow-net-compare-discharge) — Soil Mechanics, chapter 7
- [Earth dam with filter, seepage quantity](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aearth-dam-horizontal-filter-seepage) — Soil Mechanics, chapter 7
- [Top flow line, dam with horizontal filter](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Atop-flow-line-horizontal-filter) — Soil Mechanics, chapter 7

## Related in other subjects

- [Confined versus unconfined aquifer](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Aconfined-unconfined-aquifer) — Engineering Geology II, chapter 3, asked 4×
- [Confined versus unconfined aquifer](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aconfined-versus-unconfined-aquifer) — Engineering Geology I, chapter 6, asked 2×
- [Reservoir intake for an earth dam](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Areservoir-intake-earth-dam) — Water Supply Engineering, chapter 5, asked 2×
- [Earth dam with drain pipe: phreatic coordinates](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aearthen-dam-drain-pipe-phreatic) — Hydropower Engineering, chapter 4