Lecture 14: Groundwater Flashcards
-Water in the Lithosphere -Groundwater Flow -Aquifers and Aquicludes -Dissolution and Precipitating in Groundwater
What is groundwater
Water below the Earth’s surface the fills voids in soils and rocks.
How does recharge occur?
It occurs when water enters into the subsurface and becomes groundwater by percolating into soil or rocks at the surface.
What are the two zones of groundwater?
- The Vadose Zone
2. The Saturated Zone
The Vadose Zone
That region nearest to the surface where pores or fractures in the subsurface are not entirely filled with water.
The Saturated Zone
That region under the vadose zone that is filled with water.
-Where an aquifer begins
Water table
The surface where the vadose zone meets the saturated zone.
Porosity
The amount of pore space in a geologic medium.
Permeability
A measure of the ease with which a fluid can flow through a geologic medium.
How does the water table change with the landscape and seasons?
- Subdued imitation of the landscape (rises with hills and becomes lower in valleys)
- Position varies with seasons
What drives groundwater flow?
Flows from regions of lower pressure, driven by the force of gravity.
What does the hydraulic head do?
Measures the pressure difference that drives groundwater flow.
Groundwater discharge
A region at which groundwater emerges at the surface.
-Common discharge areas include surface water bodies.
What are springs?
They are natural points of groundwater discharge that occur when the water table or a permeability boundary intersects the land surface.
What is an aquifer?
Are units if geologic media that have sufficient capacity and high enough permeability to supply water at a rate useful to humans.
-Google definition: A body of permeable rock which can contain or transmit groundwater.
What is an aquiclude?
Are units of geologic media that considerably slow or stop the flow of water.
-Google definition: Any geological formation that absorbs and holds water but does not transmit it at a sufficient rate to supply springs, wells, etc.
What are the two kinds of aquifer?
- Unconfined aquifer
2. Confined aquifer
What is an unconfined aquifer?
Is an aquifer where the upper boundary is defined by the water table.
What is a confined aquifer?
Is an aquifer where the upper boundary is defined by an aquiclude.
How can a cone of depression form in the water table with a well in an unconfined aquifer?
If rate of groundwater withdrawal exceeds rate of local groundwater flow at a well.
Wells in confined (artesian) aquifers
Water is often under pressure.
-If a well is drilled into a confined aquifer, the water can rise to a level close to that of the water table in the recharge area.
What does the dissolution of minerals depend on?
Depends on the groundwater chemistry, especially pH.
-Occurs when minerals dissolve into the groundwater.
What is the precipitation of minerals?
Occurs when ions dissolved in groundwater come out of the solution due to changes in factors such as pH, temperature, pressure or effects of evaporation.
What are types of karst topography?
- Cave systems
- Sinkholes (collapsed cave roof)
- Pillars of rock isolated by dissolution of surrounding materials.
What are stalactites?
An icicle-shaped formation that hangs from the ceiling of a cave and is produced by minerals that re-precipitate from water dripping through the cave ceiling.
What are stalagmites?
A formation that rises from the floor of a cave due to the accumulation of re-precipitated minerals dripping off of stalactites.
What is cement?
Mineral deposits in small pore spaces of sediment or rocks.
