Geological factors for hydrogeological condition

Hydrogeological conditions mean how groundwater occurs and moves in an area: aquifer type, depth of the water table, yield and quality. The following geological factors control them.

1. Lithology: Gravel and sand have high porosity and permeability and form good aquifers; clay, shale and unfractured crystalline rocks hold water but yield little (aquicludes or aquitards).
2. Stratigraphy and sequence of beds: Alternation of permeable and impermeable layers produces confined (artesian) and unconfined aquifers and perched water tables.
3. Geological structure:
   • Folds: synclines store water and give artesian conditions; anticlines may shed water.
   • Faults: may act as conduits (broken zone) or barriers (fault gouge) and give springs.
   • Joints and fractures give secondary porosity in hard rocks.
   • Dip: decides direction of water flow and recharge area.
4. Weathering: weathered zones add porosity and permeability near the surface.
5. Solution features: limestone with caves and channels gives karst aquifers.
6. Topography and geomorphology: valleys, plains and terraces control recharge and discharge; flat plains favour deep aquifers.
7. Recharge conditions: rainfall, rivers, snow melt, infiltration through soil.
8. Igneous intrusions: impermeable dykes and sills act as barriers and form springs.
9. Sediment origin and depositional environment: alluvial fans and river terraces give coarse, permeable recharge zones, while basin centres have fine-grained beds that act as confining layers.

Together these factors decide whether water is stored in unconfined, confined, perched or fractured-rock aquifers.