Lectures 26, Marshak Ch. 17

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WATER
1. Where is it and how much is there? 2. What
controls its movement? 3. What is the future
availability of water and the impact of
climate change?
2
Water Cycle
Hydrologic cycle the movement of water on,
above, and below the surface of the Earth
In addition to shallow ground water, the deep
subsurface contains saline (salty) brines that
form from the reaction of water with rock and
minerals
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Water Cycle
Lots of water in the oceansnot so much freshwater
Reservoir Volume of Water (106 km3) Percent
Oceans 1370 97.25
Ice 29 2.05
Groundwater 9.5 0.68
Lakes 0.125 0.01
Soil moisture 0.065 0.005
Atmosphere 0.013 0.001
Rivers 0.0017 0.0001
Biosphere 0.0006 0.00004
About 80 of river and groundwater use in USA is
for irrigation and agriculture
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Temperature and the Water Cycle
Saturation vapor pressure pressure of a vapor is
in equilibrium with non-vapor (liquid) phases

• Increases with temperature
• 7 increase in atmospheric water vapor with
  every 1C warming
• Warmer Air can hold more water vapor Cooling
  causes condensation
• What will be the effect of global temperature
  increase?

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Water Cycle
Cycling of water is linked to global circulation

• Intertropical convergence zone
• Subtropical deserts

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WATER WHERE IS IT AND HOW DOES IT
MOVE? Aquifers and Aquitards
POROSITY PROPOSTION OF PORES RELATIVE TO
VOLUME PERMEABILITY INTER-CONNECTEDNESS OF PORES
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Porosities of various materialsLake-bottom
mud gt40 Loose sand gt25 Sandstone 5
30 Shale lt10Marble lt3 Obsidian lt1
Limestone
Shale
PermeabilityWhen pore spacesare
connected, fluids (blue)can flow.
Marble Granite
Poorly sortedsandstone
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Capillaryaction abovesaturation level
UNSATURATED ZONE
SATURATED ZONE
Water table head (H) is the elevationof the
water table above a base level h1 gt h2. Because
of gradient, water always is flowing.
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Recharge versus Discharge --controlled by
porosity and flow rates
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Darcys law measures the volume of water moving
along in a given time interval. It is measured
in m3/sec. Darcys law states also that the
velocity of this movement is proportional to the
hydraulic conductivity and HG (gradient)
?h/d. Q (volume) A (area)K (permeablilty)HG
(gradient) where KSize of PipeResistance to
FlowDrive for Flow
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Tap water
Water towersand artesianwells functionby
virtue of thesame physicalprinciples (head).
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Oases as an expression of aquifers
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STRESS ON THE FRESHWATER SYSTEM
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Annual precipitation (above) is low in the higher
great plains and mountain west. Groundwater
shortages are therefore likely in view of the
large needs of agriculture (irrigation). The
watershed of the Colorado River (right) cannot
provide enough for the large metropolitan
centers, such as Phoenix, Los Angeles, or San
Diego, in the very near future.
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In S. Dakota, the aquifer is confined.
The Ogallala Aquifer Its likely to run dry in
20 years
Profile along A-A in Nebraska on map, shows
theunconfined nature of the aquifer.
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Excess drawdown lowerswater table, and can
cause wells to go dry
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Fresh-water is lighter than salty
water.Saltwater intrusion is caused by
over-pumping of groundwater.
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Previously
Today
Note the saltwater intrusion (red arrows)
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POLLUTION
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Contaminant plumes in cross- section (above) and
in mapview (right).
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• Pall Life Sciences troubles
• They started in 1986 with the discovery of a
  dioxane leak
• They involve a possibly carcinogenic substance,
  dioxane (when administered in large doses, it is
  lethal to animals), but it should not be
  confused with the very toxic dioxin
• Dioxane spread in subsurface aquifers way beyond
  expectation
• Underground geological structures are of glacial
  origin and difficult to map or predict
• Dioxane may reach the Huron River through the
  Honey Creek tributary and can then contaminate
  all of Ann Arbors
• drinking water
• Clean up is costing more than 5M per year, but
  the public is not satisfied a major P.R.
  disaster.

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Pall Life Sciences in west Ann Arbor has a
dioxane leak problem in the subsurface that
simply wont go away.
1. Water is pumped from one of the purge wells
scattered on Pall's property and surrounding
areas (see next slide).2. Pre-treated water is
stored in a lined lagoon, the Red Pond.3. During
treatment, sulfuric acid is added to the water,
lowering the pH to about that of lemon juice, to
make treatment easier. Water is pumped into a
machine that exposes it to hydrogen peroxide
and 4.9 seconds of ultraviolet light, destroying
most of the dioxane. After treatment, the pH is
raised back to normal levels with sodium
hydroxide. Sodium bisulfite is added to help
destroy the excess hydrogen peroxide.4.
Water goes into the Green Pond and is
retested.5. Clean water is pumped into a
tributary of Honey Creek, which flows into
the Huron River.
Plume of pollutant
Dioxane is a solvent that isfound in shampoo.
It was used by Pall (then Gelman)to construct
filters.
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Freshwater and Climate Change
Freshwater stress is increasing The hydrologic
cycle is intensifying. This means more
precipitation and evaporation, more floods and
droughts.

• Growing demand (population growth) and Overuse
  
• Saline intrusion
• Pollution
• Climate Change Effects

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Precipitation
Precipitation distribution and rate

• Change in distribution of precipitation toward
  higher latitudes
• More heavy precipitation events (2-4 increase
  in frequency of heavy precipitation events)

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Intensification of Water Cycle
Increasing global temperature will intensify the
hydrologic cycle
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Drought
Droughts have expanded and intensified

• Palmer drought index measures severity of
  drought (0 none, -4 severe) and rainfall (4
  extreme)

IPCC, 2007
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