---
title: "Aquifer formation in Terai and mountains"
subject: "Engineering Geology II"
chapter: 3
key: "semester_4/engineering_geology_ii:aquifer-formation-terai-mountain"
source: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/aquifer-formation-terai-mountain
site: BCT Engineering
---

# Aquifer formation in Terai and mountains

Engineering Geology II · Chapter 3: Hydrogeology

- Asked in: 2081 Chaitra, 1.5+1.5 marks; 2068 Bhadra, 2.5 marks (asked 2 times)
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/aquifer-formation-terai-mountain
- Whole chapter: https://www.bctengineer.com/md/semester_4/engineering_geology_ii/chapter-3

## Question

What are the factors for the formation of aquifer systems in the Terai and mountain regions of Nepal?

## Short answer

In the Terai, thick alluvial gravel and sand alternating with clay form multiple unconfined and deep confined aquifers, recharged by momsoon and rivers via the Bhabar zone. In mountains, water occurs in fractures, joints, weathered rock, colluvium, and intermontane basin sediments, with recharge from rain and snowmelt.

## Answer

#### Terai (plain) aquifers
1. **Thick alluvium** brought by the rivers from the Himalaya: gravel and sand (coarse, permeable) alternate with silt and clay (impermeable).
2. **Slope change:** at the foot of the Churia range, coarse boulders form the Bhabar zone, which is the recharge area; to the south, finer sediments form confining clay beds, producing confined aquifers.
3. **Recharge** from heavy monsoon rainfall, rivers, canals and irrigation fields.
4. **Basin subsidence** gives great sediment thickness (hundreds of metres), allowing multiple aquifer layers.
5. **Shallow unconfined aquifer** in the upper sand, and **deep confined aquifers** under the clay layers.

#### Mountain aquifers
1. **Rock type:** metamorphic and igneous rocks have little primary porosity; water occurs in **fractures, joints, fault zones and weathered layer**.
2. **Structure:** folds, faults and foliation control springs and groundwater paths; permeable and impermeable layers produce contact springs.
3. **Surficial deposits:** colluvium, landslide debris, river terraces, moraines and glacial deposits store water.
4. **Intermontane basins** (Kathmandu, Pokhara) have thick lake and river sediments forming confined and unconfined aquifers.
5. **Recharge** from rain, snow melt and glaciers; steep slopes give rapid run-off and limited recharge.
6. **Limestone** areas give karst aquifers with caves and big springs.

## Check yourself

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

1. Why is the Bhabar zone a recharge area?
   A. Coarse boulders at Churia foot are highly permeable
   B. It is covered by clay
   C. It is bedrock
   D. It is a lake
   Answer: A. Coarse sediments absorb rain and river water, recharging aquifers; finer clay to the south confines them. (Key point: Terai recharge)

2. Where does water occur in mountain metamorphic and igneous rocks?
   A. In fractures, joints, fault zones and weathered layer
   B. In primary pores
   C. In deep gravel
   D. In clay
   Answer: A. These rocks have little primary porosity, so water is in fractures and weathered zones. (Key point: Mountain aquifers)

3. What does basin subsidence in the Terai allow?
   A. Great sediment thickness with multiple aquifer layers
   B. Removal of sediment
   C. Dry ground
   D. Bedrock outcrops
   Answer: A. Subsidence accumulates hundreds of metres of sediment and multiple aquifers. (Key point: Subsidence)

## Related in Engineering Geology II

- [Aquifer systems of Nepal](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Aaquifer-systems-nepal) — Engineering Geology II, chapter 3, asked 6×
- [Major discontinuity systems of Nepal Himalaya](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Anepal-discontinuity-systems) — Engineering Geology II, chapter 2, asked 12×
- [Factors causing hazards in Nepal Himalaya](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Anepal-himalaya-hazard-factors) — Engineering Geology II, chapter 5

## Related in other subjects

- [Plate boundary and mountain formation](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aplate-boundary-and-mountain-formation) — Engineering Geology I, chapter 2
- [Short note: Mountain system](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Ashort-note-mountain-system) — Engineering Geology I, chapter 2, asked 2×
- [Micro and macro factors hindering generation in Nepal](https://www.bctengineer.com/question.md?key=semester_7%2Futilization_of_electrical_energy%3Afactors-hindering-generation-nepal) — Utilization of Electrical Energy, chapter 1
- [Quality; QA vs QC; factors in Nepal](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Aquality-qa-qc-nepal-factors) — Project Engineering, chapter 4