2. Overview
The supply of water available for use
Groundwater
aquifers
examples of aquifers as resources
Global distribution of water resources
Pollution
3. Water Resources
Very little of the earth’s water is available in a form directly
utilizable by people; that is, as water resources.
Most surface water resources come from surplus (SURPL)
utilization
Groundwater comprises a large percentage of freshwater
resources
4. Groundwater
Groundwater lies beneath the surface of
the earth, but is affected by surface
supply
Groundwater is affected by changes to all
of the earth’s spheres due to linkage
through the hydrologic cycle
Percolation
5. Groundwater Concepts
Water percolates downward through permeable
rock through the zone of aeration
rock pores are unsaturated by water, many contain air
Water then accumulates in the zone of saturation
all rock pores contain water
The water table is the upper surface of the zone
of saturation
its surface follows the contours of the ground above
the water table controls the movement of surface
water
6. Porosity
describes the size, shape, arrangement, cementation,
and compaction of subsurface material
Permeable/Impermeable
Whether or not a subsurface structure permits the flow
of water
Aquifer
A layer of rock that is permeable to water flow in
useable amounts
unconsolidated aquifer: loose sand and gravel
consolidated aquifer: porous rock, often sandstone or
limestone
Aquiclude
A layer of rock that is impermeable to water flow in
usable amounts
7. Confined Aquifer
A layer of permeable rock between two
impermeable layers
An aquifer between two aquicludes
Unconfined Aquifer
An aquifer without an overlying aquiclude
Perched Aquifer
an aquifer created by a small aquiclude at
a higher level than the water table
8. Intersections of the water table with the
surface
Springs: groundwater flows out of the
ground
Effluent streams: supplied by surrounding
aquifer
Influent streams: supply the local aquifer
Artesian water
Water in confined aquifers are under the pressure
of their own weight, creating a pressure level
(potentiometric surface), beneath this surface,
water flows from the pressure of its weight
9. Aquifer recharge area
Surface area where water enters an aquifer to
recharge it.
Differ for confined and unconfined aquifers
Drawdown
Lowering of the water table due to removal of
water
Occurs if rate of pumping or removal exceeds
the horizontal flow of water in the aquifer
Cone of depression
The shape of the drawn down water table
surrounding a well
10. Groundwater mining
The act of removing water from an aquifer
at a rate greater than its flow and recharge
capacities
Collapsing aquifers: water in aquifers
often provide support for the porous rock,
its removal could result in the rock
collapsing, in which case the capacity of
the aquifer is greatly reduced
Seawater intrusion
Contamination of an aquifer by seawater
due to over-pumping the aquifer
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15. High Plains Aquifer
World’s largest known aquifer
Charged from the meltwaters of retreating glaciers
Only moderate precipitation today
Heavy groundwater mining over the past 100
years, the last 50 especially
120,000 wells provide water for 14 million acres
(170,000 wells in 1978), pumping 26 billion cubic meters
of water per year
Water table has dropped 30 meters over last 50 years,
averaging a 2 meter drop per year since 1980.
If mining stopped, it would take 1000 years to recharge
Water used to irrigate grain crops (wheat, sorghum and
corn, providing 40% of cattle feed) and cotton
Projected: Half of the area (2/3 of Texas portion)
destroyed by 2020.
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18. The Middle East
Groundwater supplies are rapidly being
depleted
Salt water incursion for tens of kilometers
inland in Saudi Arabia
Solutions:
Desalinization plants
4000 in the world, 60% in Saudi Arabia
Pipeline from Turkey
19. Global Water Resources
Supply and demand for water are not evenly
distributed over the world
Supply is affected by climatic variability
Demand is a product of:
population (and growth)
level of development
agriculture relies on precipitation (PRECIP), augmented by
irrigation (SURPL, ΔSTRG)
industry relies more heavily on surplus water
affluence
accessibility
Increased demand for water results in greater
reliance on the utilization of surface and
ground water (SURPL and STRG)
can cause rivers to run dry (Colorado R., Yellow
R.)
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23. Pollution
Groundwater flows at a slower rate than surface
water
Surface water contamination is quickly purged
(elsewhere)
Groundwater contamination is permanent and difficult
to remediate
Sources: industry, landfills, hazardous and toxic
waste dumps, agriculture (herbicides, pesticides
and fertilizer), septic tanks
10,000 suspected leaking gas tanks at service stations
nationwide
Surface water contamination concentrates
pollutants downstream
High cancer rates in New Orleans
Dead Zone in Gulf of Mexico
