Groundwater Hydrology

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Groundwater Hydrology

• What is Groundwater?
• What is Groundwater Hydrology?
• The Geology of Groundwater
• Groundwater Recharge
• Aquifers
• Groundwater Movement
• Age of Groundwater
• Locating and Mapping Groundwater
• Drilling a Groundwater Well

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From Chapter 2
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Groundwater Hydrology

• What is Groundwater?
• What is Groundwater Hydrology?
• The Geology of Groundwater
• Groundwater Recharge
• Aquifers
• Groundwater Movement
• Age of Groundwater
• Locating and Mapping Groundwater
• Drilling a Groundwater Well

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What is Groundwater?

• Found in the subsurface, inside pores within soil
  and rock
• Spelled either as two words, Ground Water, or as
  one, Groundwater
• Groundwater is the largest source of freshwater
  on earth, and was little used until recently.
• With electricity and the modern pump, groundwater
  has become very important to agriculture, cities,
  and industries.
• It is usually much cleaner than surface water.

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Figure 4.2 This map of major aquifers in the
United States shows an interesting distribution
of groundwater formations.
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Groundwater Hydrology

• What is Groundwater?
• What is Groundwater Hydrology?
• The Geology of Groundwater
• Groundwater Recharge
• Aquifers
• Groundwater Movement
• Age of Groundwater
• Locating and Mapping Groundwater
• Drilling a Groundwater Well

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What is Groundwater Hydrology?

• It is the study of the characteristics, movement,
  and occurrence of water found below the surface.
• Groundwater and aquifers are like surface water
  and watersheds
• An aquifer is a geologic unit that transmits
  water.
• Piezometric surfaces are used to map water
  levels, similar to topographic lines on maps.
• Each aquifer has its own piezometric surface.
• The water level elevation in wells are used to
  create the piezometric surface.

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Groundwater Hydrology

• What is Groundwater?
• What is Groundwater Hydrology?
• The Geology of Groundwater
• Groundwater Recharge
• Aquifers
• Groundwater Movement
• Age of Groundwater
• Locating and Mapping Groundwater
• Drilling a Groundwater Well

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The Geology of Groundwater

• Sedimentary Rocks
• sandstone, shale, limestone, conglomerate
• Glaciated Terrain
• large valleys and basins were carved out
• sediments (sands, clays) were left behind
• Alluvial Valleys and Fans
• along rivers and streams
• Tectonic Formations
• solid rock is fractured by pressures due to
  earths movement

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Figure 4.3 Continental glaciers of the most
recent Ice Age in North America (approximately
20,000 years ago) reached as far south as the
Ohio and Missouri River Valleys.
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Aletsch Glacier, Switzerland, Wikipedia
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Wikipedia
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Alluvial valley complex in Death Valley, CA space
shuttle image, USGS
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Alluvial fan, Idaho, http//www.gly.uga.edu/railsb
ack/FieldImages.html
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Figure 4.5 Ms. Cech inspects rock fractures
along the Big Thompson River near Estes Park,
Colorado.
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Groundwater Hydrology

• What is Groundwater?
• What is Groundwater Hydrology?
• The Geology of Groundwater
• Groundwater Recharge
• Aquifers
• Groundwater Movement
• Age of Groundwater
• Locating and Mapping Groundwater
• Drilling a Groundwater Well

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Groundwater Recharge

• Water that replenishes aquifers
• Usually from surface water or precipitation that
  infiltrates, and then percolates through the
  vadose zone
• Recharge happens when percolating water finally
  reaches the water table, which is the top of the
  saturated zone.
• Above the water table is the unsaturated zone
  where water is held by capillary forces
• The root zone may capture some water that
  infiltrates and lift it back to the atmosphere.

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Figure 4.6 Lakes and wetland complexes often
exist in areas with shallow groundwater
elevations that intercept the land surface..
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Groundwater Recharge
Evapotranspiration
Infiltration
Overland flow
Percolation
Saturated zone
Fetter, Applied Hydrology
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Groundwater Hydrology

• What is Groundwater?
• What is Groundwater Hydrology?
• The Geology of Groundwater
• Groundwater Recharge
• Aquifers
• Groundwater Movement
• Age of Groundwater
• Locating and Mapping Groundwater
• Drilling a Groundwater Well

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Aquifers

• Water-bearing geologic formation that can store
  and yield usable amounts of water
• Aquifer types
• unconsolidated, consolidated, fractured
• perched, unconfined, confined, artesian
• thermal springs
• Aquifer properties
• porosity volume of pores (voids) per total
  volume of aquifer
• n Vv / Tt

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Unconfined Aquifer
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Land surface elevation in meters
Figure 4.10 The Ogallala Aquifer provides water
to irrigators, cities, and other groundwater
users in parts of South Dakota, Nebraska,
Wyoming, Colorado, Kansas, Oklahoma, Texas, and
New Mexico.
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Confined Aquifer
Figure 4.7 Two conditions are necessary to
create an artesian groundwater system a confined
aquifer and sufficient pressure in the aquifer to
force water in a well or other opening to rise
above the static water level of the aquifer.
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Thermal Springs and Geysers
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Aquifer Porosity
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Example Porosity Calculation

• Take a 1000-mL beaker (1 liter)
• Fill it with sand to the top
• Measure how much water it takes to fill the
  beaker to the top (say 300 mL)
• The porosity (300 mL) / (1000 mL) 30

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Groundwater Hydrology

• What is Groundwater?
• What is Groundwater Hydrology?
• The Geology of Groundwater
• Groundwater Recharge
• Aquifers
• Groundwater Movement
• Age of Groundwater
• Locating and Mapping Groundwater
• Drilling a Groundwater Well

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Groundwater Movement

• Water moves because of two factors
• The force pushing through the subsurface
• The permeability of the geologic media
• Darcys Law says that the flux of water (flow per
  unit area) is calculated using these two factors
• q K i
• q flux of water, ft / s
• K hydraulic conductivity, ft / s
• i hydraulic gradient, ft / ft

Note they both have the same units
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• The hydraulic conductivity, K, is a measure of
  the permeability of the aquifer
• gravels have large hydraulic conductivities
• clays and solid rock have small values
• The hydraulic gradient is a measure of the force
  acting on the water
• it is like the slope of the land surface, water
  flows faster where it is steep
• i dh / dl slope of the water surface
• h is the hydraulic head, or water level in a well
• dh is the change in water level between two wells
• dl is the distance between the wells
• determines the direction of flow.

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Direction of Flow?
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Geological Regions of Georgia
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Georgia Piedmont Region
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h 55 m
h 50 m
K 5 m/day
dl 1,000 m
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h 55 m
h 50 m
dh 5 m
K 5 m/day
dl 1,000 m
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h 55 m
h 50 m
dh 5 m
K 5 m/day
dh/dl 5/1,000 0.005
dl 1,000 m
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h 55 m
h 50 m
dh 5 m
K 5 m/day
dh/dl 5/1,000 0.005
dl 1,000 m
q K i 5 x 0.005 q 0.025 m/day
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Karst Aquifers
Wikipedia
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Underground Rivers?
Only in Karst aquifers!! Wikipedia
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Specific Yield

• Volume of water that can be removed per unit
  volume of aquifer
• less than the porosity - hard to get the last
  drop!

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Specific Yield Calculation

• Take a 1000-mL beaker (1 liter)
• Fill it with sand to the top
• Measure how much water it takes to fill the
  beaker to the top (say 300 mL)
• The porosity (300 mL) / (1000 mL) 30
• We pour the water out and 250 mL is collected
• What is the specific yield?
• (250 mL) / (1000 mL) 25
• Cant get the last drop!

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Groundwater Hydrology

• What is Groundwater?
• What is Groundwater Hydrology?
• The Geology of Groundwater
• Groundwater Recharge
• Aquifers
• Groundwater Movement
• Age of Groundwater
• Locating and Mapping Groundwater
• Drilling a Groundwater Well

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Age of Groundwater

• Time it takes for water to move through the
  subsurface
• Maybe 1 to 25 years in aquifers near Athens
• Up to 30,000 years for water down on the coast

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Groundwater Hydrology

• What is Groundwater?
• What is Groundwater Hydrology?
• The Geology of Groundwater
• Groundwater Recharge
• Aquifers
• Groundwater Movement
• Age of Groundwater
• Locating and Mapping Groundwater
• Drilling a Groundwater Well

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Locating and Mapping Groundwater

• The first step is to generate a piezometric
  surface, which maps water table elevation
• Wells are plotted on a map, and water levels in
  the wells are indicated
• Lines of constant water level elevations are
  plotted (called equipotentials)
• Flowlines (also call streamlines) are drawn so
  that they are perpendicular to the equipotential
  lines
• Local rivers, lakes, and other surface water
  features are plotted on the map.

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Groundwater Hydrology

• What is Groundwater?
• What is Groundwater Hydrology?
• The Geology of Groundwater
• Groundwater Recharge
• Aquifers
• Groundwater Movement
• Age of Groundwater
• Locating and Mapping Groundwater
• Drilling a Groundwater Well

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Drilling a Groundwater Well

• Various methods are available for drilling a well
• A simple method is the auger method, which uses a
  screw-like bit. This works in soft materials
• For solid rock, a simple technique is the hammer
  or percussion method which pounds a hole in the
  rock
• Rotary methods uses a harden steel bit tipped
  with diamonds to cut through the rock. Either
  water, air or mud can be used to lubricate and to
  lift the cuttings.

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Well Components

• A well pad is placed on the surface to hold up
  the well.
• A blank casing is used from the surface down to
  the aquifer. Clay or concrete fills the space
  outside the casing.
• A screened casing is used in the aquifer. Sand or
  gravel fills the space outside the casing
• A submerged turbine pump lifts the water to the
  surface. The motor that drives the pump is either
  on the surface or also submerged.

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Piedmont Wells
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Cone of depression in potentiometric surface near
Albany GA
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South Georgia Water Use

• Floridan aquifer important supply for drinking
  water and irrigation water
• Water wars between Georgia and Florida over flow
  in the Apalachicola River
• Are irrigation wells reducing flow in the Flint
  and Apalachicola Rivers?

Chattahoochee
Flint
Apalachicola
Wikipedia
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Stream Depletion Factors

• Used to assess the effects of well pumping on
  stream flow
• Depend on
• the distance to the stream (less effect with
  greater distance)
• properties of the aquifer

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Quiz 4

• Two wells are located 1 km (1,000 meters) apart.
  Well A has a water level of 105 m and Well B has
  a water level of 102 m.
• Which direction is the groundwater flowing? From
  Well ____ to Well ____
• What is the hydraulic gradient between the two
  wells?
• What is the flux (flow rate) if the hydraulic
  conductivity is K 10 m/day?
• A one-liter (1,000 mL) beaker is filled with sand
  and filled to the top with water.
• What is the porosity of the material if 250 mL
  was required to fill the beaker?
• We pour the water out, and 200 mL is collected.
  What happened to the rest of the water?
• What would the porosity be if we use clay instead
  of sand? (more, less, the same)
• How much water would pour out if we use clay
  instead of sand? (more, less, the same)
• True - False Questions
• T / F An aquiclude is a geologic formation that
  holds a lot of water.
• T / F Perched aquifers are a kind of artesian
  aquifer.
• T / F The Ogallala aquifer is the major aquifer
  in the Southeastern U.S.
• T / F The water table is found at the top of
  the saturated zone.
• T / F The two factors that determine how much
  horsepower is needed to lift water are the amount
  of water that must be lifted and the height that
  you must lift the water.
• Explain what Stream Depletion Factors are used for