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

# Geology in reservoir site selection

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

- Asked in: 2073 Bhadra, 3 marks
- Video: [Required Geological Consideration for Selecting Dam and Reservoir Site - Geological Investigation](https://www.youtube.com/watch?v=TPg6afvpYx4) — 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/reservoir-site-selection
- Whole chapter: https://www.bctengineer.com/md/semester_4/engineering_geology_ii/chapter-4

## Question

Describe the geological considerations for reservoir site selection.

## Short answer

A site needs watertight impermeable rock (shale, clay, massive crystalline) and no cavernous limestone, open joints or permeable faults. Beds dipping upstream are preferred; groundwater level must be higher than reservoir level. Avoid landslide-prone slopes, active faults, erodible catchments causing siltation, and soluble rocks that degrade water quality.

## Answer

A reservoir must hold water, remain stable and stay silt-free as long as possible.

#### Geological considerations
1. **Watertightness of the basin and rim:** impermeable rocks (shale, clay, massive crystalline rock) are suitable. Avoid cavernous limestone, highly jointed or fractured rock, coarse gravel and permeable fault zones, which cause leakage. Check there is no low saddle or permeable gap along the rim and divide.
2. **Geological structure:** beds dipping upstream or toward the reservoir are favourable; downstream dip may lead to leakage. Faults and folds may be leakage channels.
3. **Stability of reservoir banks:** avoid landslide-prone slopes; filling can reactivate old slides; slide into the reservoir causes waves.
4. **Water table:** the groundwater level on both sides should be higher than the reservoir level, to avoid loss.
5. **Sedimentation:** catchment with weak, erodible rocks and landslides leads to quick siltation.
6. **Seismicity:** reservoir-induced seismicity; avoid active faults.
7. **Water quality:** soluble salts (gypsum, rock salt) spoil the water.
8. **Valuable resources** (minerals, forests, settlements) that would be submerged.
9. **Construction materials** nearby.

## Check yourself

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

1. Which rocks suit a reservoir?
   A. Cavernous limestone
   B. Fractured rock
   C. Impermeable rocks such as shale, clay and massive crystalline rock
   D. Coarse gravel
   Answer: C. Permeable rocks leak. (Key point: Watertightness)

2. Why should groundwater on both sides be higher than the reservoir level?
   A. To increase siltation
   B. To reduce stability
   C. To raise earthquakes
   D. To avoid loss of water from the reservoir
   Answer: D. Otherwise water leaks out. (Key point: Water table)

3. Fast siltation occurs when the catchment has
   A. Weak, erodible rocks and landslides
   B. Massive hard rock
   C. Dense forest only
   D. Flat cover
   Answer: A. It shortens reservoir life. (Key point: Sedimentation)

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- [Influence of fault on site selection](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Ainfluence-of-fault-on-site) — Engineering Geology I, chapter 5