Groundwater: Porosity, Permeability, and Karst Processes

Porosity

Amount of pore spaces present in a rock unit

Permeability

Connectedness of pore spaces in rock unit

High porosity

Holds lots of water (lots of holes)

Low porosity

Holds little water (solid rock → no space)

High permeability

Water moves easily

Low permeability

Water barely moves

Saturated zones

Subsurface zone that contains water within pore spaces

Unsaturated zones

Subsurface zone that contains mostly air within pore spaces

Unconfined aquifer

Occurs within the saturated zone, and is bounded by impermeable layer beneath and the unsaturated zone above

Confined aquifer

Occurs within the saturated zone, and is bounded by two impermeable layers

Perched aquifer

Occurs on a local scale within the unsaturated zone, infiltration is stopped by an impermeable layer above the water table

Hydraulic head

Level of water within a well above sea level

Causes of groundwater contamination - Natural processes

Rock dissolution can release harmful species into water (ex: Arsenic in India)

Causes of groundwater contamination - Human processes

Anthropogenic land use (ex: landfills, fertilizers, ice melt, etc.)

Karst

The surface expression due to subsurface dissolution

Karst early stages

Small sink holes; caves, disappearing streams

Karst middle stages

Growing sinkholes and caves, disappearing streams exposed

Karst later stages

All limestone dissolved, occasional resistant/residual towers