Water Resources
Hydrologic Cycle
Hydrosphere: All the water at or near
the surface of the earth
 Amount of water essentially constant
and moves between different reservoirs
 100 million billion gallons move through
Hydrologic Cycle
 Oceans account for ~96%, Fresh water
lakes and streams for only 0.016% of
all water

Distribution of Water
Hydrologic Cycle
Thousands of km3/yr
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+
Ground water
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22% of all fresh water occur
underground
Aquifer: Underground formation that
holds and yields water
A good aquifer needs to be both
porous and permeable
Porosity and Permeability

Porosity: Proportion of void space: pore
space, cracks, vesicles
• Gravel : 25-45% (1K - 10K), Clay: 45-55%(<.01)
• sandstone: 5-30% (0.3 - 3), Granite: <1 to 5%(.003 to
.00003)
• higher porosity in well rounded, equigranular, coarse
grained rocks
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Permeability: Measure of how readily fluid
passes through a material
• Depends on the size of the pores and how well
they are interconnected
• Clay has high porosity but low permeabilty
Less porosity
porosity
permeability
Clay 45-55%
<0.01 m/day
sand
0.01 - 10
30-52%
gravel 25 - 45%
1000 to 10,000
Subsurface
Water
Zone of Aeration or
Vadose Zone or
Unsaturated Zone:
Overlies Phreatic
Zone. Pore spaces
Saturated
Zone
partly filled with
water. Contains soil
moisture.
Zone of Saturation or Phreatic
Zone: saturated
zone overlying impermeable bed rock. Water fills all
the available pore spaces
Water Table: top of the zone of saturation where
not confined by impermeable rock
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Water table follows the topography but more
gently
Intersection of water table and ground
surface produces lakes, streams, spring,
wetlands…
Ground water flows from higher elevation to
Darcy’s law
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Hydraulic Gradient: Slope of the
ground water table
Rate of flow is proportional to the
hydraulic gradient
Aquifer
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Recharge: Process of replenishment of
Ground Water by infiltration, migration and
percolation
Aquifer: A rock that holds enough water
and transmits it rapidly. Porous and
Permeable. Sandstone and Coarse Clastic
Sedimentary rocks make good aquifers
Aquitard and Aquiclude: Rocks of low and
very low permeability e.g., shale, slate
Perched water table: Local aquifer in
Vadose Zone
Confined and Unconfined Aquifer
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Unconfined Aquifer: open to
atmosphere e.g., overlain by
permeable rocks and soils
Confined aquifer: sandwiched
between aquitards
• Artesian System: Water rises above the
level in aquifer because of hydrostatic
pressure

Potentiometric surface: Height to
which water pressure would raise the
water.
Artesian
System: Water rises above the
level in aquifer because of hydrostatic
pressure
Potentiometric
surface: Height to which
water pressure would raise the water.
Consequences of Ground Water
Withdrawal

Lowering of Water Table

Cone of depression: Circular lowering of water
immediately around a well
Consequences of Ground Water
Withdrawal
–overlapping cones of depression causes lowering
of regional water table
–Water mining: rate of recharge too slow for
replenishment in human life time
Compaction and Subsurface subsidence
Consequences of Ground Water
Withdrawal….

Compaction and Subsurface
subsidence
• Building damage, collapse
• flooding and coastal erosion
e.g., Venice,
Galveston/Houston (80 sq
km permanently flooded),
San Joaquin Valley (9m
subsidence)
• Pumping in of water no
solution
Land subsidence in
San Joaquin Valley ,
California
The High Plains Aquifer
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The High Plains is a 174,000-square-mile area of flat to
gently rolling terrain that includes parts of eight States
from South Dakota to Texas.
moderate precipitation but in general has a low naturalrecharge rate to the ground-water system.
Unconsolidated alluvial deposits that form a water-table
aquifer called the High Plains aquifer underlie the
region.
Since early 1800s, irrigation water pumped from the
aquifer has made the High Plains one of the Nation’s
most important agricultural areas.
the intense use of ground water for irrigation has
caused upto 100m decline in water-level in parts of
Kansas, New Mexico, Oklahoma, and Texas.
Changes in groundwater levels in the High
Plains aquifer from
before ground-water
development to 1997.
(V.L. McGuire, U.S.
Geological Survey,
written commun.,
1998.)
The Gulf Coastal Plain Aquifer System
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The Gulf Coastal Plain aquifer system underlie
about 290,000 square miles extending from Texas
to westernmost Florida, including offshore areas to
the edge of the Continental Shelf.
Water withdrawals from the aquifer system have
caused
• lowering of hydraulic heads at and near
pumping centers;
• reduced discharges to streams, lakes, and
wetlands;
• induced movement of saltwater into parts of
aquifers that previously contained freshwater;
• and caused land subsidence in some areas as a
result of the compaction of interbedded clays
within aquifers.
Land subsidence in Houston
Flooding in coastal Galveston because of subsidence
Saltwater
Intrusion
–upconing below cone of
depression
–Aquifer below Brooklyn, NY
destroyed
–Serious problem in Gulf Coast and
California
Salt water
incursion
in caostal
aquifer
Salt water intrusion in
Miami-Dade
Extent of
salt water
incursion in
MiamiDade
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Sinkholes
• forms in areas with abundant water
and soluble bedrock (gypsum or
limestone)
• collapse follows ground water
withdrawal
Stalagtites
Stalagmites
Dripstones in a cavern
Urbanisation and ground water

Loss of Recharge
• Impermeable cover retards recharge
• Filling of wetlands kills recharge area
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Well planned holding pond can help
in recharging ground water
Water Quality
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Most freshwater contain dissolved
substances
concentrations are described in ppm or ppb
TDS=Total Dissolved Solids
• 500 to 1000 ppm for drinking water
• 2000 ppm for livestock
• some solids (e.g., Iron, Sulfur) more
harmful than others (e.g. calcium)
• synthetic chemicals can be toxic at ppb
level
Radioactive elements pose special hazard
• Uranium, Radium, Radon
Hard water
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Hard Water:
• Common in limestone country
• contains dissolved Ca and Mg;
problematic if >100 ppm
• problem with soap
• leaves deposits in plumbing and in
appliances
• can be cured with water softener
typically ion exchange through zeolites
Water Use in US
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4200 billion gallons of precipitation
2750 billion gallons lost by
evaporation
1400 billion gallons available for
consumption
Biological need : 1 gal/person/day
US consumption: 1800 gal/person/day
= 400 billion gallons per day for the entire US
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Offstream Use: water diverted from
source e.g.,for irrigation or thermal
power generation
• Consumptive: water used up
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For farming, drinking or lost by evaporation
Instream: water returns to flow:
e.g., for hydroelectric power
generation
Water Use …contd
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Main Uses:
• Thermoelectric Power
 Surface: Ground water = 67:33
 Consumed 2%, Return Flow 98%
• Irrigation
 Surface: Ground water = 63:33
 Consumed 56%, Loss 20%, Return Flow 24%
• Industrial
 Surface 67% (saline 12%), Ground water 15%
(1% saline), Public Supply 19%
 Consumption 15%, Return Flow 85%
• Domestic
 Public Supply 86%, Ground Water 13%, Surface
1%
 Consumption 23%, Return Flow 77%
Irrigation and Ground water
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Thus, irrigation is the major
consumer of ground water
Western states are the major
drawers of ground water causing
serious environmental problems
Most of the precipitation is in the eastern states but…
Most of the water withdrawal is in the western states (see
also the next slide)
•Total withdrawal increased
from 1950 to 1980 and has
held steady since then
although population has
increased by 16%
•Withdrawal for
thermoelectric power
generation 190,000 Mgal/day:
largest of any other category
•Higher water price, more
public awareness,
conservation, better farming
and industrial techniques will
keep water demand in check
Water Rights
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Riparian Rights (Eastern USA):
• Every landowner can make reasonable use of
lake or stream or water flowing through or
bordering his property
• Municipalities have the right of eminent
domain: at times of scarcity, cities get their
requirement first
• Sale of riparian rights allowed in some states
• Practical in regions of plentiful water
Law of Prior Appropiation
• First come, first served
• Settlers can lay claim to certain amount of
water which will be honored for perpetuity
• The oldest claim are honored first and any left
over goes to the next claimant and so on..
• Los Angeles bought up water rights in 1900
from areas far and wide, some even from
Arizona. Now people in those areas are very
unhappy about the arrangement
Story of Colorado River
Colorado River basin
The Colorado River flows through
Utah to Lake Powell, thence
through the northwest corner of
Arizona to Lake Mead. From
Hoover Dam it flows southward to
Mexico forming the border between
Nevada, California and Arizona,
and yielding major diversions to
central Arizona and southern
California. The river is the lifeblood
of the southwestern US and its
development and management
have been the focus of attention by
the member states for more than a
century. Waters of the Colorado
River System have been
apportioned by a treaty with
Mexico, compacts, and a Supreme
Court decree to the seven basin
states.
Colorado River Compact
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The Colorado River Compact of 1922 divided the use of
waters of the Colorado River System between the Upper
and Lower Colorado River Basin.
It apportioned in perpetuity to the Upper and Lower Basin,
respectively, the beneficial consumptive use of 7.5 million
acre feet (maf) of water per annum.
It also provided that the Upper Basin will not cause the flow
of the river at Lee Ferry to be depleted below an aggregate
of 75 maf for any period of ten consecutive years.
The Mexican Treaty of 1944 allotted to Mexico a guaranteed
annual quantity of 1.5 maf. These amounts, when
combined, exceed the river's long-term average annual
flow.
These apportions were decided during a particularly wet
climatic period. At present, the flow in Colorado does not
add up to all the apportionments
Within Colorado water
allocations are based on
the Doctrine of Prior
Appropriation or the
First-in-Time, First-inRight Doctrine. This
doctrine is found in most
arid states because
when there is too little
water to satisfy all
users, sharing of the
remaining water would
be of little value to any
user. But a large part of
the Colorado river water
is diverted to Los
Angeles on the basis of
this doctrine
Conservation
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Shift water-hungry crops to regions
with more rainfall
Use drip irrigation to reduce
evaporation loss
Use pipes to reduce transport loss
Water lawns in morning and evening
or opt for no lawn
Direct storm water in recharge
basins
Interbasinal transfer
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Transfer water from water-surplus
regions to water-deficient regions
• California : Los Angeles aqueduct moves
150 million gallons/ day from east of Sierra
Nevada to LA
• New York: Water supply to NYC from Finger
Lakes region
• political problems
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Desalination
• Filtration, distillation
• Expensive, limited