Lesson 14: Ground Water Flashcards
What is the main use of groundwater in the U.S.?
Irrigation (Agriculture)
Where does the groundwater stay in the rock?
in open spaces (pores) within rocks and unconsolidated sediments.
What is porosity?
The percentage of open pore space within an unconsolidated sediment/rock
What is permeability?
How connected the pore spaces are to one another; controlled solely by pore geometry
Compare porosity and permeability
Porosity: determines how much groundwater can be stored
Permeability: determines how well water can flow from one pore to another
Define vadose zone.
The unsaturated zone above the zone of saturation; includes both air and water
Define saturated zone.
The zone of saturation where all pore spaces are completely filled with water; water in this zone is groundwater
Define water table.
The upper limit of the zone of saturation.
Compare losing and gaining streams.
Losing Streams: streams lose water to the groundwater system by outflow through the streambed; the water table is lower than the level of a stream
Gaining Streams: streams gain water from the inflow of groundwater through the streambed; the water table is higher than the level of the stream.
What is an Aquitard?
an impermeable layer that hinders/prevents groundwater movement
What is an Aquifer?
A porous and permeable zone that is saturated with water that is recharged as surface water seeps downward
What types of rocks make an aquitard?
Shale/mudrock and clay
What types of rock make an Aquifer?
Sand and glacial till
What is a confined aquifer?
An aquifer that has permeable rock units enclosed within impermeable rock units; recharged in highlands where permeable rocks are exposed
What is an unconfined aquifer?
An aquifer that is connected to the surface by open pore spaces through which it can be recharged
What is a perched aquifer?
When there is a limited aquitard; it may be a good source of water during some parts of the year, but is very thin and small, and can be depleted easily.
What is drawdown?
As water is withdrawn from a well, the surrounding water table is lowered.
Where do drawdowns form?
at the water table
What is a cone of depression?
the lowering effect on the water table
Where does a cone of depression form?
at the base of a well stem
What are artesian wells?
a system where groundwater under pressure rises above the level of the aquifer
Where do artesian wells form?
in a confined and inclined aquifer
What is the main corrosive component in groundwater?
Carbonic acid
How is Carlsbad Cavern in New Mexico different than most other caverns?
they formed due to reactions with sulfuric acid-bearing water
What are the 5 common rocks that easily dissolve?
- Limestone
- Dolostone
- Halite/rock salt
- Gypsum/Rock Gypsum
- Marble
What is Karst topography?
a landscape that has been shaped mainly by the dissolving power of groundwater
What are the different karst landscapes?
- Sinkholes
- Caves/caverns
- Tower karst
- Disappearing streams
- Springs
How do sinkholes form? (3) types
- Dissolution: Rainfall and surface water percolate through joints of a limestone, dissolved carbonate rock is carried away from the surface, and a depression gradually forms
- Cover-Subsidence: Granular sediments spall into secondary openings in the underlying rocks, and a column of overlying sediments settles into the vacated spaces, forming a noticeable depression in the land surface
- Cover-Collapse: Sediments spall into a cavity as spalling continues the cohesive covering sediments form a structural arch. The cavity migrates up by progressive roof collapse and eventually branches creating a sudden and dramatic sinkhole
How do caves form?
By chemical dissolution resulting from circulating groundwater
How do tower karsts form?
limestone rises above the surrounding landscape in highly eroded karst regions
What are disappearing streams?
streams that disappear into cave openings that flow directly into the groundwater system.
What are springs?
Groundwater that is becoming surface water
What is speleothem?
A general name for dripstone features
How do stalactites differ from stalagmites?
Stalactites hang from the ceiling
Stalagmites form from the ground
___ accounts for the largest percentage of groundwater usage in the US
Irrigation
Porosity may be defined as:
the percentage of pore spaces in a rock/sediment
_____ refers to how connected pore spaces are to one another.
Permeability
______ are characteristics found in all good aquifers.
High porosity and high permeability
The unsaturated (vadose) zone…
lies above the water table
Highly impermeable layers such as compacted clay/shale are known as _____.
Aquitards.
The lowering effect on the water table at the base of the well stem is called a ______.
cone of depression
In an ______ system groundwater under pressure rises above the level of the aquifer.
artesian
Does permeability depend on fluid properties?
No
Which of the following sedimentary rocks is NOT easily dissolved?
a. limestone
b. sandstone
c. dolostone
d. Halite
b. sandstone
____ topography is a landscape that has been shaped mainly by the dissolving power of groundwater.
Karst
