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Aquifer systems of Nepal

Short answer

Terai: thick Quaternary alluvium; Bhabar unconfined coarse aquifer, southern Terai has shallow unconfined and deep confined aquifers. Hills: fractured/weathered rock and springs, intermontane basin sediment aquifers. High mountains: fractures and glacial debris, low yield.

Describe the different aquifer systems of Nepal (Terai, hills and mountains).

An aquifer is a saturated geological formation that stores and transmits useful quantities of water. In Nepal, aquifer systems differ by physiographic region.

1. Terai (Indo-Gangetic plain)

  • Made of thick Quaternary alluvium (gravel, sand, silt, clay), hundreds of metres thick.
  • Northern Terai (Bhabar zone): coarse boulder-gravel at the foot of the Churia; very high permeability; unconfined aquifer with deep water table; main recharge zone.
  • Southern Terai: alternating sand and clay layers; shallow unconfined aquifer (up to about 30-50 m) and deep confined (artesian) aquifers, with flowing wells in places.
  • Highest groundwater potential; shallow tube wells and deep tube wells widely used. Arsenic problem in shallow aquifers.

2. Hills (Siwalik, Mahabharat and Middle Mountains)

  • Rock aquifers: fractured and weathered phyllite, schist, quartzite, limestone and Siwalik sandstone.
  • Groundwater occurs in joints, fault zones, weathered layer and colluvial/river terrace deposits.
  • Yield is low and variable; springs are the main source. Intermontane basins (Kathmandu, Pokhara) have thick lacustrine and fluvial sediments with good confined and unconfined aquifers.

3. High mountains

  • Crystalline rocks (gneiss, granite) and glacial and moraine deposits.
  • Groundwater only in fractures and glacial debris; snow melt and glaciers are the main sources; springs on slopes. Potential is small and poorly known.

✓ Answer checked by Claude Opus 5.5 (high effort)

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