GROUNDWATER

Groundwater

represents the largest reservoir of freshwater that is readily available to humans.

Geological roles

Erosional agent.
Streamflow equalizer

Zone of soil moisture / soil zone

Near surface zone that wets the surface of grains and organic material making up the soil.

Unsaturated zone

Zone where water clings too tightly to the soil, sediment, and rock.

Saturation zone

Zone where all of the open spaces in sediment and rock are completely filled with water.

Water table

Upper limit of the zone of saturation.

Water table (behavior)

Shape replicates the surface and changes depending on rainwater supply.

Porosity

Percentage of the total volume of rock or sediment that consists of pore spaces that can store groundwater.

Voids

may be spaces between particles, joints, faults, cavities in dissolved materials, vesicles.

Permeability

Ability of a material to transmit fluid along connected and large pores.

Aquitard

Impermeable layers that hinder or prevent water movement. Example: clay.

Aquifer

Permeable rock strata or sediments that transmit groundwater freely. Example: sand and gravel.

Groundwater flow (unsaturated zone)

Downward movement due to pull of gravity.

Groundwater flow (saturated zone)

Moves downward, sideways, upward due to pressure and pull of gravity.

Hydraulic head

Energy from elevation and pressure which causes water to flow. Groundwater flows from higher hydraulic head to lower hydraulic head.

Recharge area

Water enters the ground via downward flow direction.

Discharge area

Water flows back up to the surface.

Groundwater flow factors

Complex, crooked network pathway.
Friction with surrounding rocks.
Water table slope.
Material permeability.

Spring

Natural outlets from which groundwater flows.

Well

Holes that people dig or drill.

Spring (mechanism)

Groundwater flow when water table intersects the ground surface.

Hot spring

+6 to 9C mean annual air temperature of the specific area.
Formed by:

1. Circulating groundwater at higher depths

   1. Heated water rise to surface

Geyser

Ejects water with great force at various intervals that may release steam.
Occurs where extensive underground chambers exist within hot igneous rocks.

Formational process:

1. Cool groundwater is heated

2. Heating causes water to expand

3. Water is ejected → lowering pressure

4. Leftover water turns into steam

5. Geyser erupts

6. Extruded water infiltrates the ground

   1. Cycle repeats

Well (operation)

Hole bored into the zone of saturation where groundwater moves to the surface.

Drawdown

Depression in the water table due to continuous well pumping.

Artesian well

Penetrates confined aquifers in which water is under enough pressure to rise on its own above the surface of the aquifer.

Caverns

Formed due to groundwater erosion.

Cavern (formation)

Created at or below the water table in the zone of saturation.

1. Acidic water follows rock weaknesses

2. Dissolves surrounding rocks

3. Cavities grow forming caverns

   1. Dissolved materials flow to streams and oceans

Travertine

Calcium carbonate left by endless dripping of water of caverns above the water table in the unsaturated zone.
Stalactites: hanging from the ceiling of the cavern formed where water seeps through cracks above.
Stalagmites: develops on the floor of a cavern reaching to the ceiling.

Sinkhole

Irregular depressions common in karst areas.

Sinkhole formation

As rain falls, it absorbs carbon dioxide, making percolating water slightly acidic. As this water migrates downward, the carbonate bedrock is slowly dissolved, creating bedrock voids.
Over time, the underground void becomes larger as soil and rock from above fall into the cavity and are washed away.
The void continues to grow and stops upward toward the surface.
Eventually, the structural integrity of the overlying material is breached and a sinkhole forms.

Tower karst

Isolated steep sided hills that rise abruptly from the ground.
Rapid karst development in tropical climates due to abundant rainfall and greater availability of carbon dioxide.