Geology Exam 2: Chapter 11
Where are some geographical examples of where this has occurred?
- Venice, Italy - Houston / Galveston Bay, Texas - San Joaquin Valley, CA
How does urbanization impact groundwater recharge?
- can modify surface water runoff patterns and stream channels - if you develop structures over confined aquifers, you can reduce recharge rates dramatically - filling in wetlands can interfere with recharge - water pollution
How do karst systems play a role in aquifers?
- since limestone can be fracture, it serves as a conduit for surface water draining into ground water - the caves of karst typography can serve as storage chambers for water - when caves are interconnected that are called karst aquifers
What are some of the consequences on the soil when the water table is lowered?
1. Compaction: the weight of the overlying soil and rocks compacts the soil, reducing its porosity and waterholding capacity. This can lead to... 2. Subsidence: a lowering of the entire ground surface. In extreme cases, regions may subside by several meters. 3. Sinkhole formation: locally formed pits (often in areas underlain by limestone caves)
Have an understanding of the case studies for the Colorado River Basin, Ogallala Aquifer, Aral Sea, Lake Chad. For the history of the Colorado River Basin, know to the level of detail listed in the lecture handout
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What are some examples of "impermeable cover"?
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What is karst topography?
A ragged surface characterized by sinkholes and underground caves
artesian well
A well in which water rises because of pressure within the aquifer
vadose zone
A zone above the water table and below the land surface that is not saturated with water the pore spaces in the soil are partly filled with water and partly filled with air
What are some of the benefits and drawbacks of desalination?
Benefits: removes harmful metals, chemicals, and bacteria that could be in your water source Drawbacks: costly
Why is groundwater sometimes used as a water supply preferentially over surface water in some regions of the country?
Even with an abundant surface water supply, groundwater is often tapped because it can be a more reliable resource in arid or seasonally dry areas. Groundwater is also naturally filtered, though it can still become polluted
Is the water table always below the ground surface?
NOT always: where it intersects the ground, the water table may form a spring, lake, or wetland
What is saltwater intrusion?
Over-pumping of groundwater in some coastal areas can lead to the infiltration of salt-water
porosity and permeability
Porosity - a measure of how much fluid a sediment or rock can store. The more pore space between grains, the higher the rock's porosity Permeability - the ease with which a fluid can move through a porous rock.
Which sector is the biggest consumer of groundwater?
Power plants do not use groundwater. The biggest consumer of groundwater is still irrigation
Aquitard
Rock units that may be porous, but limit (slow down) water flow due to low permeabilit
What is an example of a sedimentary rock that has a high porosity but a low permeability?
Shale (made out of clay)
Looking at 11.2 (p. 254), which sector of the US is the biggest user of surface water?
The biggest user is power generation, however, this water is typically dumped back into the same water source it was taken from, so the water is not consumed. The biggest consumer would be agriculture irrigation.
unconfined aquifer
an aquifer made of porous rock covered by soil out of which water can easily flow
confined aquifer
an aquifer surrounded by a layer of impermeable rock or clay that impedes water flow
cone of depression
an area lacking groundwater due to the rapid withdrawal by a well.
Aquifer
an underground layer of water-bearing, permeable rock
Why are these types of rocks susceptible to sinkholes?
because naturally be dissolved by groundwater circulating through them
What is hard water?
contains substantial amounts of calcium and magnesium
Why is saltwater intrusion such a danger to freshwater aquifers?
decreases fresh water storage in aquifers
Groundwater is found in which zone?
phreatic zone
What do the terms recharge and discharge refer to with regard to the flow of groundwater?
recharge: When groundwater levels rise due to new water arriving discharge: when the levels fall due to water exiting the area (ex: enters a stream, or a well)
perched water table
refers to a small aquitard that supports an aquifer above it; but above the water table. It is a local zone of saturation that lies above the regional water table
What rock type causes it?
soluble rock types such as limestone, marble, and gypsum
phreatic zone
the lower region where the soil is fully saturated with water. This zone may be up to a few km in thickness
How is water quality typically measured?
the sum of dissolved solid chemicals in the water
What is the boundary between the two zones called?
water table