---
title: "Geology in dam site selection"
subject: "Engineering Geology II"
chapter: 4
key: "semester_4/engineering_geology_ii:dam-site-selection"
source: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/dam-site-selection
site: BCT Engineering
---

# Geology in dam site selection

Engineering Geology II · Chapter 4: Engineering geology in site selection, investigation & construction/excavation

- Asked in: 2072 Magh, 3 marks
- Video: [Geological Considerations in the selection of Dam Site](https://www.youtube.com/watch?v=LUKJeSNmKow) — Narasaraopeta Engineering College
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/dam-site-selection
- Whole chapter: https://www.bctengineer.com/md/semester_4/engineering_geology_ii/chapter-4

## Question

What are the engineering geological factors to be considered for dam site selection?

## Short answer

Factors include strong, massive, low-weathering foundation rock; favourable geological structure (preferably upstream-dipping beds); watertightness (avoid limestone cavities, open joints); stable abutments; narrow valley; low seismicity; available construction materials; and manageable seepage and sedimentation.

## Answer

A dam must be founded on ground that is strong, stable and watertight.

#### Geological factors
1. **Foundation rock:** strong, massive, sound, with low weathering. Granite, gneiss, quartzite and massive sandstone are good; weak shale, phyllite, schist and soft clay are poor. The type of dam (concrete gravity, arch, earth fill) is chosen from the foundation.
2. **Geological structure:** avoid faults, shear zones, folds with weak planes, closely jointed rock; bedding should be favourable (beds dipping upstream are best; beds dipping downstream, especially at low angles, are dangerous because the dam can slide along them).
3. **Watertightness:** avoid highly permeable rock, solution cavities in limestone, and open joints; check with Lugeon tests; plan grouting and cut-off.
4. **Abutments:** stable, no landslides or rock fall; adequate rock cover.
5. **Valley shape:** narrow, with sound rock at shallow depth, so smaller dam volume.
6. **Seismicity:** avoid active faults near the site; design for earthquakes.
7. **Reservoir:** rim and basin should be watertight and stable (see reservoir site).
8. **Construction materials:** aggregate, sand, clay and rock fill near the site.
9. **Groundwater and seepage conditions** around the dam.
10. **Sedimentation** rate of the catchment.

## Check yourself

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

1. Which rocks are good dam foundations?
   A. Granite, gneiss, quartzite and massive sandstone
   B. Weak shale
   C. Phyllite
   D. Soft clay
   Answer: A. Dam type is chosen from foundation. (Key point: Foundation rock)

2. Which bedding is best?
   A. Steep dip downstream
   B. Dipping upstream
   C. Dip along a fault
   D. Horizontal weak shale
   Answer: B. Steep downstream dip risks sliding. (Key point: Bedding)

3. Watertightness is checked by
   A. Colour
   B. Plate load
   C. Lugeon tests, with grouting and cut-off planned
   D. Schmidt hammer
   Answer: C. Solution cavities and open joints leak. (Key point: Watertightness)

## Related in Engineering Geology II

- [Road, dam and foundation site geology](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Aroad-dam-building-bridge-foundation) — Engineering Geology II, chapter 4
- [Geology in tunnel site selection](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Atunnel-site-selection) — Engineering Geology II, chapter 4, asked 4×
- [Geology in bridge site selection](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Abridge-site-selection) — Engineering Geology II, chapter 4, asked 6×
- [Geology in reservoir site selection](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Areservoir-site-selection) — Engineering Geology II, chapter 4
- [Geology for dam and bridge sites](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Adam-bridge-site-considerations) — Engineering Geology II, chapter 4
- [Geological factors for hydrogeological condition](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Ahydrogeological-condition-factors) — Engineering Geology II, chapter 3, asked 9×

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- [Dam site evaluation factors; gravity dam failure modes](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Agravity-dam-site-evaluation-failure-modes) — Hydropower Engineering, chapter 4
- [Reservoir intake and site selection factors](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Areservoir-intake-site-factors) — Water Supply Engineering, chapter 5, asked 2×
- [Distribution substation site selection factors](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Asubstation-site-location-factors) — Industrial Power Distribution and Illumination, chapter 4