Chapter Fifteen
Groundwater
Groundwater
 Earth’s hydrosphere extends from top of atmosphere to ~ 10 km (6 mi) below the Earth’s
surface. Groundwater, 0.6% of world’s water, accounts for 97% of Earth’s supply of unfrozen
water.
 Surface waters from rivers, lakes or precipitation enter the ground under the influence of
gravity
The amount of water that enters the ground depends on the topography, geologic
composition and vegetation
 The surface water will percolate downwards until it reaches a zone where all the pore spaces
are saturated with water
Factors affecting infiltration
Moisture through tree
Surface distribution of water
Movement and Distribution of GW
 Water bound to clay minerals
 Zone of aeration: unsaturated zone
 Zone of Saturation
 Water Table: Upper surface of the zone of saturation
 Capillary Fringe: Lower part of the aeration zone – range from few tens of cm to
several meters
Groundwater Movement
 For groundwater to flow- need porous and permeable materials
 Porosity is the percent of pore spaces in relation to the total soil/rock/sediment volume (Primary
Porosity: Porosity that develops as a rock forms; Secondary Porosity: Develops after a rock has formed)
 Permeability is a measure of the ability of rock/sediment to transmit fluid
 Groundwater flow occurs when there is a hydraulic gradient
 Hydraulic conductivity is the ability to transmit groundwater. Typical groundwater flow is slow ~0.5 –
1.5 cm/day
humans.
(0.2 - 0.6 in/day). The slow movement stores the water making it available to
The subsurface distribution of water
Primary porosity of sedimentary rocks
Pore connection and Permeability
Pore connection and Permeability – contd.
Hydraulic gradient
Variations in water table depth
Water Table configuration
Perched water pools
Tapping Groundwater aquifer
 Groundwater depth is a reflection of local topography and prevailing climate
 Aquifers are permeable water-bearing bodies of geologic materials
Unconfined and Confined aquifers
 Aquiclude and Aquitard
 Artesian flow- water flows to the surface from wells without pumping
Potentiometric surface
Natural Springs
Geysers- intermittent surface emission of hot water/steam
How groundwater flows
 Groundwater flow potential
– Gravity
– Pressure from overlying water and rocks
– Hydraulic Gradient: Difference in potential / distance
– Hydraulic conductivity: Measure of conductivity – size, shape & degree of sorting of its
grains – coarse, well-rounded, well-sorted and gravel – high conductivity
– Darcy’s principle (19th Century): Rate at which water flows is  difference in potential
 hydraulic conductivity
Groundwater flow – contd.
 Mesuring the Rate of GW Flow:
– Dye injection method
– Carbon –14 dating method
Groundwater Flow Rate:
Average: 0.5 to 1.5 cm/day
Fastest: 100 m / day
Composite Landscape
Artesian aquifer
Desert Oases
Municipal water tower
Natural springs
Natural springs – contd.
Geysers
Locating groundwater and features associated with pumping
 Locating Groundwater
Mapping
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Water table from well records, lake, river levels, drilling test holes
 Features Associated with Pumping
 Cone of depression- local depression in water around pumping well
 Subsidence- compressed land due to aquifer depletion
 Salt water intrusion- due to over pumping along coast line
 Greater demand for water- leads to groundwater depletion and introduction of pollutant
 Solutions- enhance recharge, water transfer, conservation, desalinization, and use of iceberg
Search for Groundwater
 Characteristics of the Water Table:
– Depends on Typical depth
– Relationship to topography
– Response to Climatic Fluctuations
AQUIFERS:
– Aquifer: Permeable, water-bearing bodies of geological material
– Unconfined aquifer: Not overlain by impermeable cap tock
– Confined Aquifer: Found in greater depths, between aquiclude (impermeable rock layers)
and Aquitard
Search for water
Overuse of groundwater
Water table around a well
The effect of development on a water table
Subsidence in a coastal area
Subsidence in a coastal area – contd.
Groundwater contamination / purification
 Natural occurring solutes- Chlorine, Arsenic, Mercury, and Selenium
 Manufacturing contaminants- from household products: cans of paint, solvent, cleanser
etc.
 Natural Groundwater Purification
Filtration- adhere to clay particles
Decomposition- some decompose completely by oxidation
Bacteria action- organic solids consumed by microorganis
Saltwater intrusion
Salt water intrusion – contd.
Stratigraphy of Yucca Mountain
Landfill sites
Landfill sites – contd.
Products of Groundwater
 Karsts
 Water reacts with carbon dioxide to form weak carbonic acid which then attacks limestone
H2O + CO2 => H2CO3 + CaCO3 => Ca++ HCO3 –
 Caves- natural underground cavities and most common geological product of limestone dissolution
 Cave deposits- spelotherms are deposits on cave surfaces in a variety of forms: travertine, Stalactite,
Stalagmite, banded draperies or drip curtains
 Growth of spelotherm- depends on the solution and porosity of surface material, climate, topography,
and vegetation

State 1 of cave formation
State 2 of Cave formation
Stalactite, stalagmite and travertine
Cave formation
Speleothem growth and climate
Rise and fall of sea level
Karsts Topography
Surface expression of the geology of dissolved limestone and work of near surface water
 Cave and Karsts landscapes are extremely sensitive- so need to be protected
 Landform
Sinkholes-circular surface depression
Disappearing Streams- flow through sinkholes may emerge as spring several kilometers
away
Natural Bridge- series of neighboring sinkholes expand and join together
Worldwide distribution of karst landform
Typical landforms associated with karst topography
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Summary
What percentage of the world’s water is GW
What is groundwater recharge
What is water table
Where will the primary porosity be maximum
When groundwater flows upward against gravity?
Darcy’s principle
How groundwater flow is measured
Which isotope is used to measure rate of GW flow?
Typical rate of flow of Groundwater
Unconfined aquifer, confined aquifer
Temperature of GW is???
When does saltwater intrusion occur?
How grading steep slopes enhance GW recharge?