1. Chapter 13: Groundwater Aquifers Groundwater Movement Erosion
Deposition
Resources

2. Groundwater Groundwater is an open, dynamic system
Gravity is primary driving force
Pulls water down
Water enters the system at the ground surface through recharge
Leaves the system through discharge

3. Porosity Percent of the total volume that is open space
Affected by the size and shape of particles
Increased by fracturing or dissolution
Decreased by compaction and cementation
Well sorted sediments have higher porosity than poorly sorted sediments

4. Permeability Permeability is a property of the rock
Other liquids such as oil flow through rock
Density and viscosity influence flow rate
Size and connectedness of pores
How easily fluid may pass through a rock
A measure of how well the pores are connected, and how straight a path a fluid follows

5. The Water Table
Water is found at some depth everywhere beneath the Earth’s surface
The water table defines the boundary below which all pore spaces are filled with water
The volume of pore spaces decreases as you go deeper into the crust
Usable water is restricted to a few hundred meters below the surface

6. The Water Table
Forms the boundary between the Saturated Zone and the Unsaturated Zone
The unsaturated zone is also referred zone of aeration

7. Water Table
The water table may be shallow or deep as a function of permeability of bedrock and climate.
The water table intersects the land surface in lakes and streams.
In the location shown at right, the water table lies at a depth of about two feet.
In deserts, the water table may reside hundreds of feet below the surface.

8. Aquifers Aquifer Aquitard Aquiclude Confining Unit
A layer or zone in the subsurface capable of producing water to a well (in usable quantity)
Aquitard
Aquiclude
Confining Unit
A layer or zone in the subsurface that does not easily allow water to pass through it

9. Aquifers Unconfined Aquifer
An aquifer that has highly permeable material extending from ground surface downward to an aquitard at its base
Recharge is from seepage, lateral flow of groundwater, or upward leakage through the aquitard
Also called a water table aquifer

10. Aquifers Perched Aquifer
A layer of saturated soil found in the unsaturated zone
Underlain by an aquitard of limited aerial extent
Recharge is only from seepage
Water flows to the edge and continues down

11. Aquifers Confined Aquifer
Aquitards form confining units top and bottom
Recharge occurs in an area some distance away or by leakage through the aquitard
The water level (potentiometric surface) may be above the top of the aquifer
Artesian aquifers have a potentiometric surface above ground surface

12. Groundwater Flow Groundwater flows due to the force of gravity
Hydraulic gradient defines the water table slope
Hydraulic head is the elevation of the water table at a given point
The water table surface usually mimics the ground surface contours

13. Groundwater Flow Flow is from high to low hydraulic head
Gravity creates water pressure
Pressure forces water to flow downward to the water table
Water continues to flow downward and outward
Flow is along curved path

14. Recharge Groundwater and surface water are intimately linked
Recharge as meteoric water flows into the ground
Usually at higher elevation
Where permeable rocks are exposed at surface
In arid regions, streams and lakes can act as recharge zones
min maximum
Steepness of slope: steep flat
Rate at which rain falls: rapid slow
Vegetation: sparse dense
Permeability: non-permeable perm
unpaved paved

15. Discharge Groundwater and surface water are intimately linked
Discharge occurs to lakes, streams and wetlands
Maintains flow in streams during dry periods
Artificial discharge is the result of wells

16. Natural Discharge
Springs include any natural flow of water from the ground surface
Intersection of water table-ground surface
Springs are caused by:
Aquitards intersecting the ground surface
Faults cutting through an artesian aquifer
Fractures in volcanic rock
Road cuts

17. Natural Discharge: Springs

18. Homework What controls how fast groundwater moves?
Hydraulic conductivity
Permeability
Viscosity
Gradient
Is groundwater movement important?

19. Wells Before Pumping During Pumping Water table is nearly horizontal
Water table is depressed as water is withdrawn from the aquifer
Forms cone of depression

20. Thermal Springs & Geysers
Geysers and hot springs require:
Hot rock bodies to heat groundwater
Fracture systems to transmit water
Large supply of groundwater
Geysers such as Old Faithful are the results of this process

21. Thermal Springs & Geysers
Hot water contains thermal energy and dissolved ions
Geothermal energy taps heat source
Many mineral deposits are produced by hot water interacting with cooling igneous intrusions

22. Thermal Springs & Geysers
Hot water contains thermal energy and dissolved ions
Geothermal energy taps heat source
Many mineral deposits are produced by hot water interacting with cooling igneous intrusions
The One Ring to Rule Them All

23. Groundwater Erosion
Groundwater chemically weathers & erodes bedrock through dissolution
Subsurface dissolution forms:
Caves
Sinkholes
Karst topography

29. Ha Long Bay, Viet Nam

30. Karst Topography
Karst topography is found in areas that have carbonate, sulfate, or salt beds at or near the ground surface
And the climate is…?
Characterized by:
Solution valleys with remnant walls and towers
Disappearing streams
Sinkholes

31. Karst in Chinese Landscapes

32. Groundwater Deposits
Minerals may precipitate from dissolved ions in groundwater
CO2 in water dissipates into air
pH of water changes
CaCO3 is precipitated
Other soluble minerals may occur
Gypsum

33. Groundwater Deposition
Richard Cindric

39. Groundwater Deposits
Minerals may precipitate from dissolved ions in groundwater
SiO2 also moves
Cement sediment
Fossil replacement

40. Groundwater Resources
Groundwater is the largest reserve of fresh water
Much larger than surface water resources
Used for drinking water, irrigation & industrial uses
Excessive use causes drawdown, sudsidence, sinkhole collapse, pollution, and disruption of ecosystems.
GROUND WATER ATLAS of the UNITED STATES
Arizona, Colorado, New Mexico, Utah, USGS HA 730-C

41. Groundwater Resources
Groundwater is the largest reserve of fresh water
Much larger than surface water resources
Used for drinking water, irrigation & industrial uses
Excessive use causes drawdown, sudsidence, sinkhole collapse, pollution, and disruption of ecosystems.
GROUND WATER ATLAS of the UNITED STATES
Arizona, Colorado, New Mexico, Utah, USGS HA 730-C

42. How do we use groundwater?
97% of unfrozen fresh water supply
50% of our drinking water
25% of water used for industrial purposes
Richard Cindric

43. Major Concepts
The movement of groundwater is controlled largely by the porosity and permeability of the rocks through which it flows.
The water table is the upper surface of the zone of saturation.
Groundwater moves slowly through the pore spaces in rocks by the pull of gravity moving from high pressure to low pressure
The natural discharge of groundwater is generally into springs, streams, marshes, and lakes.
Groundwater occurs in unconfined and confined aquifers.
Erosion by groundwater produces karst topography, with caves, sinkholes, solution valleys, and disappearing streams.
Groundwater also precipitates minerals creating deposits in caves and along fractures and cements many kinds of clastic sedimentary rocks.
Alteration of the groundwater system can produce many problems, such as pollution, subsidence, sinkhole collapse, and disruption of ecosystems.