Hydrogeology and Environmental Geology
What the exam tests
Hydrogeology and Environmental Geology covers the occurrence and movement of groundwater, aquifer properties, Kerala's well and spring systems, and environmental problems such as salinity intrusion, pollution and landslides.
Core rules
- Porosity is the fraction of void space; permeability is the ability to transmit water. Clay has high porosity but low permeability.
- Aquifer types: unconfined (water table), confined (artesian, potentiometric surface) and perched. Aquicludes and aquitards restrict flow.
- Recharge is by rainfall and infiltration; discharge is through wells, springs, evapotranspiration and base flow.
- Kerala aquifers: laterite (shallow, dug wells), fractured crystalline bedrock, and coastal sands vulnerable to seawater intrusion when over-pumped.
- Environmental issues: laterite quarrying, river sand mining, salinity intrusion, pesticide and septic pollution, and landslides on deforested Western Ghats slopes.
Worked example
A 1 km² unconfined aquifer drops 2 m when pumped; specific yield is 0.15. Volume released = area × drop × specific yield = (10⁶ m²) × 2 m × 0.15 = 3 × 10⁵ m³. Use specific yield, not porosity, because capillary forces retain part of the pore water.
Traps
Using porosity where specific yield is required. Drawing the potentiometric surface above ground level in a confined aquifer diagram when the well is not flowing. Blaming landslides on rainfall alone without slope angle, deforestation and drainage.