UNIVERSITY OF SOUTH ALABAMA
Last Time
Karst Geomorphology
GY 301: Geomorphology
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What is karst?; Chemical considerations
•
Karst landforms (small to large scale)
•
Karst features on topographic maps
Lecture 20:
Groundwater
http://wedc.lboro.ac.uk/dw/images/drawing-water-from-a-well-1.jpg
Karst Geomorphology
•
•
•
First described by Serbia Geographer Jovan Cvijić (1865–
1927)
Named after the Kras Plateau region bordering Italy and the
former Yugoslavia (now Serbia)
Distinctive landforms caused by dissolution of limestone by
water (surface and ground water)
CaCO3 ←
→ Ca2+ + CO32-
Chemical Considerations
•The relationship between PCO2
and Ca 2+/CO32- is non-linear
•Mixing any 2 waters that are
naturally saturated with Ca 2+ and
CO32- will result in a solution that
is undersaturated (e.g., dissolution
of CaCO3)
Thrailkill (1968)
Karst Topography
•
Limestone dissolution
features are abundant and
diverse both at the
surface and underground
Karst Topography
•Like meandering rivers, the degree
of karstification can be related to
“age”
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Karst Topography
Small Scale
Karst Topography
Large Scale
•rillenkarren (karren)
•solution pits
•pavements
•caves
•sinkholes
•disappearing streams
•tower karst
http://www.devsys.co.uk/Album/Places%20of%20Interest/limestone%20caves.jpg
Karst Topography
Karst Features on Maps
Caves
Large Scale
•caves
•sinkholes
•disappearing streams
•tower karst
Today’s Lecture
Hydrosphere
Groundwater
•
•
The hydrosphere and the hydrological cycle
•
Groundwater concepts
Hydrogeology concepts (Darcy’s Law, 3 point problems)
The hydrosphere is
defined as all the
water above, one and
in the Earth
hydrosphere
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Hydrological Cycle
Water in the
hydrosphere is
circulated within the
hydrological cycle
Hydrological Cycle
Most of the planet’s
water is in the oceans
(96%) followed by the
ice caps (3%) and then
groundwater (1%)
http://www.coloradocollege.edu/dept/ev/courses/EV211WWW/hydrological%20cycle.jpg
Groundwater
http://www.coloradocollege.edu/dept/ev/courses/EV211WWW/hydrological%20cycle.jpg
Water Table
Groundwater is water that infiltrates below the Earth’s surface
Porosity: percent void
space in a material
Permeability: degree of
connectivity of pores
(ability of a material to
transmit a fluid)
Common permeable
geological material
includes sandstone,
limestone, marble,
fault breccia
The water table is a planar surface that separates the saturated and
undersaturated zones
http://www.belmont.sd62.bc.ca/teacher/geology12/photos/erosion-water/permeability.gif
Water Table
http://myweb.cwpost.liu.edu/vdivener/notes/water_table.gif
Water Table Morphology
• The water table is a subdued replica of the overlying
topographic surface
Undersaturated zone (Vadose)
Straight down water movement
Saturated zone (Phreatic)
Lateral? water movement
The water table is a planar surface that separates the saturated and
undersaturated zones
http://earthsci.org/education/teacher/basicgeol/groundwa/chwattab.gif
http://myweb.cwpost.liu.edu/vdivener/notes/water_table.gif
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Water Table Morphology
• Where the water table intersects the surface there will be a
water discharge (spring, pond, lake or stream)
Water Table Morphology
• Porous layers that area capable of passing water and releasing
it at springs and/or wells are called aquifers.
http://earthsci.org/education/teacher/basicgeol/groundwa/chwattab.gif
http://www.tol.ca/files/web_images/engineering/environment/WebImages/unconfined.jpg
Water Table Morphology
• Clay layers may act as aquicludes and generate a perched water
table (a localized water table).
Water Table Morphology
• The recharge area is where the precipitation enters the
groundwater system
http://groundwater.oregonstate.edu/sites/default/files/u1/rechargeb.gif
Types of Aquifers
• Unconfined Aquifer: open to direct recharge at the Earth’s
surface
• Confined Aquifer: bracketed by aquicludes (impermeable)
• Potentiometric Surface: elevation to which the pressurized
water in a confined aquifer will rise
• Artesian Well: water rises to an elevation above the aquifer
• Flowing Artesian Well/Spring: potentiometric surface is above
the ground surface
Types of Aquifers
Potentiometric Surface:
elevation to which
the pressurized water
in a confined aquifer
will rise
Artesian Well: water
rises to an elevation
above the aquifer
Flowing Artesian
Well/Spring:
potentiometric
surface is above the
ground surface
http://www.douglas.co.us/water/images/Denver_Basin_Aquifers_clip_image004.jpg
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Anthropogenic Effects
• Pumping lowers the elevation of the local water table
(Drawdown)
Anthropogenic Effects
• Excessive pumping can severely lower the elevation of the
local water table (cone of depression)
http://myweb.cwpost.liu.edu/vdivener/notes
Anthropogenic Effects
• Which can really be bad during droughts (wells run dry)
Other Groundwater Issues
• Ground subsidence and collapse
Water Resources
• Potable groundwater is a rapidly diminishing resource
Other Groundwater Issues
• Saltwater intrusion: Salt water is more dense than fresh water
Sinkholes
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Other Groundwater Issues
• Contamination of groundwater supply
Hydrothermal Systems
• Groundwater heated by magmatic sources
Contamination Issues
• Lead (Pb): sources include atmospheric pollution and older
lead pipes
• Radioactive Waste: natural and anthropogenic sources
• Microorganisms: sewage and waste water, flooding and storm
surge
• Other chemical contaminants (solvents, gasoline, nitrates, road
salt, etc.)
Groundwater Flow (J. Connors Stuff)
• Darcy’s Law: governs the
volume of groundwater
produced at a well head
Q= A(K x h)
l
– Q is volume
– A is cross sectional area of
aquifer
– K is permeability
– h is hydraulic head
i.e., you can determine groundwater flow rates
– l is map distance
Groundwater Flow (J. Connors Stuff)
Groundwater Flow (J. Connors Stuff)
Three Point Problem
Three Point Problem
Calculate the direction of
groundwater flow based upon
water table elevations
Calculate the direction of
groundwater flow based upon
water table elevations
Sinkhole
(WE=425 ft)
Spring
(440 ft)
Water flows from high elevations to
low elevations
Well
Surface elevation: 474 ft
Dept to water: 100 ft
http://www.uwgb.edu/dutchs/Graphics-Geol/structur/manual/fig13a.gif
Chalk Board
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Upcoming Stuff
Homework
Arid Lands Geomorphology (due Friday)
Next Lecture:
Glaciers
Friday’s Lab:
Map interpretation (karst/groundwater)
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