1. Chapter 14 Groundwater

2. Importance of groundwater
Groundwater is water found in sediment, plus narrow fractures in bedrock
Groundwater is the largest reservoir of fresh water available to humans

3. Sources of Earth’s water

4. Distribution of Groundwater

5. The Water Table Water table is the upper limit of saturation
Variations in the water table
Depth is highly variable
Varies seasonally and from year to year
Shape is usually similar to surface topography

6. Factors influencing movement of groundwater - 1
Porosity – Volume of Pore Space
Permeability – the ability of a material to transmit a fluid through pore space

7. Factors influencing movement of groundwater - 2
Aquifer – a permeable rock layer or a sediment that transmits groundwater freely (such as sands and gravels)
Aquitard – an impermeable layer that hinders water movement (such as mudstone - clay)

8. Springs may result from a perched water table
Rollie’s Well

9. Features associated with Groundwater - 1
Hot springs
Water is 6-9oC warmer than the mean annual air temperature of the locality
The water for most hot springs is heated by cooling of igneous rock

10. Features associated with Groundwater -2
Geysers
Intermittent hot springs
Water erupts with great force
Occur where extensive underground chambers exist near hot igneous rock
Groundwater heats, expands, changes to steam, and erupts

12. Yellowstone Geyser erupting

13. Yellowstone Geyser Pool prior to eruption
Groundwater flows back in, lowest chamber flashes to steam, erupts again.

14. Features associated with groundwater - 3
Wells
To ensure a continuous supply of water, a well must penetrate below the water table

15. Artesian Well Model
Demo: Artesian
Discussion:
Quicksand

16. Hydraulic head and urban water supplies
Just like an artesian, saves money

17. Features associated with groundwater - 3
Wells (con’t)
Pumping of wells can cause
Drawdown (lowering) of the water table
Cone of depression in the water table

18. Formation of a cone of depression in the water table
Discharge exceeds recharge

19. Other problems associated with groundwater withdrawal
Treating groundwater as a nonrenewable resource
In many places water available to recharge aquifer is less than amount being withdrawn
“Discharge greater than Recharge

20. Other problems associated with groundwater withdrawal (Continued)
Subsidence !
Ground sinks when water is pumped from wells faster than natural recharge replaces it

21. Other problems associated with extreme groundwater withdrawal (Continued)
Dry Wells – cone of depression already seen
Saltwater contamination near coast
Contamination of Wells with sewage
Formation of Collapse Sinkholes

22. Saltwater contamination due to excessive well pumping
Wildwood Crest

23. Well design requires knowledge of local geology
Don’t fire the town engineer!

24. Geologic work of groundwater
Caverns
Most caverns are created by acidic groundwater dissolving soluble rock at or just below the surface in the zone of saturation
Acid forms as Carbonic Acid (next)

25. Geologic work of groundwater
Groundwater dissolves rock
Groundwater is often mildly acidic
Contains weak carbonic acid
Forms when rainwater dissolves carbon dioxide from the air and from decaying plants

26. Geologic work of groundwater
Groundwater dissolves rock
Carbonic acid reacts with calcite in limestone to form calcium bicarbonate, a soluble material
Later cements particles - lithification

27. Geologic work of groundwater
Caverns
Features found within caverns
Composed of dripstone (travertine)
Calcite deposited as dripping water evaporates

28. Geologic work of groundwater
Caverns
Features found within caverns
Composed of dripstone (travertine)
Collectively, they are called speleothems
Includes stalactites (hanging from the ceiling) and stalagmites (form on the floor of a cavern)

29. Geologic work of groundwater
Karst topography
Landscapes that have been shaped by the dissolving power of groundwater on limestone

30. Geologic work of groundwater
Karst topography
Some common features include
Irregular terrain
Sinkhole or sinks (formed by groundwater slowly dissolving the bedrock often accompanied by collapse)
Disappearing (aka sinking) streams

31. Stream incision, cave development and karst topography Solution

32. Sinkholes in Urban Settings
Florida sinkholes

33. End of Streams and Groundwater