Transcript Chapter 8: Major Elements

Water: Process, Supply, and Use
There is plenty of fresh water:
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Atmosphere
Rivers and streams
Lakes
Groundwater
0.001%
0.0001%
0.009%
0.31%
total 4 million km3
...but rarely where we want it in the right form
Water: Process, Supply, and Use
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Global per capita water use is 2 m3/day
US is 5 m3/day
By 2000 will use 6000 km3/yr = 5% of total in lakes
and rivers (including a huge amount in uninhabited
areas, so locally much higher %)
Of course this is renewable, but also pollutable
US Water Resources Council est. by 2020 American
water use may exceed surface resources by 13%
Most of Americans use water that has been used at least
once before
Water: Process, Supply, and Use
Surface water covered in largely in rivers section
Surface
water
supply is
controlled
largely by
precipitation
Water: Process, Supply, and Use
Areas with < 65 cm/yr
have inadequate surface
water supplies
The West (particularly
the Southwest) are
headed for trouble
How can we make up the
difference?
Water: Process, Supply, and Use
Groundwater
Fig. 10-6
Water table = top surface
of saturated zone
Capillary fringe: water
drawn up by capillary
action
Groundwater usually
flows due to slope of
water table
Water: Process, Supply, and Use
Aquifer: high porosity and permeability (+ water)
Clastic sediments
 Fractured igneous or metamorphic
 Basalts and upper brecciated zone, joints,
soil/interbeds
 Dissolved limestone
Impermeable layers are called aquitards (or aquicludes)
clay, igneous…
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Water: Process, Supply, and Use
Confined vs. unconfined aquifers
“potentiometric surface”
Artesian wells: under
pressure beneath an
aquiclude- water rises
up the well pipe
Flowing artesian wells
actually rise above
the ground surface
Water table wells are
the common type
Water: Process, Supply, and Use
The same principal works in terms of municipal water supply
Water: Process, Supply, and Use
Springs occur when
the contact between an
upper aquifer and a
lower aquitard
intersects the ground
surface
Water: Process, Supply, and Use
Where to drill and
how deep are difficult
questions and require
good subsurface data
Cost of drilling a well
averages $15/foot
10 ft. may be fine in a
floodplain
Generally deeper on
slopes of hills
A 1000’ well costs
$15,000
Water: Process, Supply, and Use
Pumping usually faster than
recharge due to limited
permeability of the aquifer
Cone of depression
Effect on neighbors
Some recovery when cease
pumping
Compaction when lose water
support can cause permanent
decrease in porosity and
permeability
Water: Process, Supply, and Use
Perched aquifer: held above the normal water
table by an aquiclude
Water: Process, Supply, and Use
Groundwater flows into an effluent stream in wet climates
This is a result of discharge from the aquifer
Groundwater flows out from an influent stream in dry climates
This results in recharge to the aquifer
Recharge areas are often far from the discharge zone or point
Water: Process, Supply, and Use
Water Supply
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Water supply depends on climate, geology,
stream flow, subsurface flow...
Budget = annual runoff + groundwater
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Cannot contain and use all runoff
Cannot extract and distribute all of groundwater
Much groundwater is available where surface
water is also
Water: Process, Supply, and Use
Water Supply
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In much of the American West there is often
little surface or groundwater
In places where there is groundwater and little
surface water, there is a tendency to overdraw,
or “mine” the aquifers (non-renewable)
Groundwater overdraft for conterminous US in 1975
(Florida in East due to saltwater encroachment)
The Ogallala (or High
Plains) Aquifer
> 170,000 mi2 and holds
> 7 x 1016 gallons of water
Charged in glacial times
(over 12,000 yrs ago)
Current recharge from
rainfall (< 16-20”/yr)
Main source of water in
several arid states
The availability of water
from the Ogallala led to
considerable agricultural
development
What do we do when the
Ogallala aquifer runs
dry?
One study said that by
2015 the Ogallala will be
so reduced and pumping
will be so expensive due
lowering of the water
table that crop yields will
be down by 80% and
300,000 people will have
to migrate away
Water: Process, Supply, and Use
Movement of water to people
1. Withdrawal: quantity
diverted or taken from
surface or groundwater (A)
2. Delivery to point of use (B)
3. Release to pt. of return (C)
4. Conveyance loss: lost in
transit (A  B)
5. Consumptive use: portion
evaporated, leaked,
transpired, or absorbed by
crops, etc.
6. Return flow: amount
returned to surface or
groundwater and available
for future use
Water: Process, Supply, and Use
Movement of water to people
California:
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Source of water is runoff in north
S. California indigenous water could support
~250,000 people
Many cities experiencing shortages, groundwater
pollution, salinization (from agriculture and
encroaching seawater), etc.
Part of Southern
California’s answer to its
water problem is an
alternative to
groundwater
withdrawal: aqueducts
and canals
Water: Process, Supply, and Use
Water Quality
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Dissolved material in ppm (or ppb)
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TDS = total dissolved solids (should be < 300-1000 ppm)
“Hard” water: > 80-100 CaCO3 – MgCO3
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Causes “scale” in boilers and hot-water pipes
Prevents soap from lathering & rinsing
Water softeners exchange Na+ for Ca++ and Mg++
Water: Process, Supply, and Use
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Water conservation is fairly effective since mid
1970’s
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Drip irrigation
Industrial conservation
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Home conservation
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Running water or
leaks (including
mains), toilets,
showers/baths, lawn
watering, letting water
run while washing
dishes...
Water: Process, Supply, and Use
Movement of water to people
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Water management
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Geologic and climatic factors as well as political
and economic
Flood prevention in times of high flow and
conservation/distribution when low
Conserve groundwater when surface water is
available: don’t mine it
Desalination may provide fresh water
Water: Process, Supply, and Use
The Colorado: a managed river
Mostly rural water is
collected and distributed by
dams, reservoirs, aqueducts,
canals, and pipes to
agriculture and millions of
urban residents
Water: Process, Supply, and Use
The Colorado: a managed river
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Flow only 3% of the Mississippi, but lifeline of most
of the Southwest
Elaborate system of distribution, allocation, rights,
legal squabbles, etc. between 7 states + Mexico
Glen Canyon dam was built at the political boundary
between the Upper and Lower Colorado districts
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Divided water rights between U & L basins
Highly variable annual flows
Evaporation and infiltration from reservoirs
Salinity and pollution
Water: Process, Supply, and Use
The Colorado: a managed river
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Allocations made following an
unusually wet decade
  over-allocation when flows
returned to normal levels
 Central Arizona Project just
finished (S. California has
used 0.6 Maf of Arizona’s
allocation)
Dams and Reservoirs
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Dams are multifunctional, but generally designed for
 Flood control
 Hydroelectric
Ancillary uses:
 Recreation
 Irrigation and municipal water supply
 Navigation
Negative effects:
 Flood large areas: affect human/animal habitat
 Interrupt fish migration
 Interrupt sediment flow
Water: Process, Supply, and Use
Water and Ecosystems
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Natural ecosystems reflect a balance between climate,
nutrients, soils, biota, hydrology...
Humans are now degrading most ecosystems on a
regional and global basis
 The most damaging effects are associated with
degraded surface water conditions
 The effects can be far-reaching: even to the oceans
(Aswan) and atmosphere (Amazon)