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GEOL g406 Environmental Geology
WATER
Process, Supply and Use
Part 1 – Surface Water and General Concepts
Read Chapter 10 in your textbook (Keller, 2000)
S. Hughes, 2003
Types of water:
Water on Earth
• Surface water = water in rivers, lakes, oceans and so on.
• Subsurface water = groundwater, connate water, soil
moisture, capillary water.
• Groundwater exists in the zone of saturation, and may be
fresh or saline.
• Meteoric water = water in circulation.
• Connate water = "fossil" water, often saline.
• Juvenile water = water from the interior of the earth.
QUESTIONS:
• Which of these can be or is polluted in some places?
• Which of these are used most by humans?
• What is the relative residence time of water in each one?
Read Tables 10.1 and 10.2 in the textbook.
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The Earth’s Water Supply
Usable water - 0.3%
Rivers
Unusable water - 99.7%
(oceans, ice caps, glaciers)
Fresh-water lakes
Ground water
Although water is abundant on a global scale, more than 99% is
unavailable for our use. A mere 0.3% is usable by humans,
with an even smaller amount accessible! The oceans, ice caps,
and glaciers contain most of the Earth’s water supplies. Ocean
water is too saline to be economically useful, while glaciers and
ice caps are "inconveniently located."
S. Hughes, 2003
GLOBAL WATER SOURCE AND VOLUME
Water source
Water volume
(in cubic km)
Percent of Total
Oceans
Icecaps, glaciers
Groundwater
Fresh water lakes
Inland seas
Soil moisture
Atmosphere
Rivers
1,230,000,000
28,600,000
8,300,000
123,000
104,000
67,000
12,700
1,200
97.2%
2.15%
0.61%
0.009%
0.008%
0.005%
0.001%
0.0001%
Total Water Volume
1,360,000,000
100%
SOURCE: USGS, 1984, The Hydrologic Cycle – Pamphlet
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Global Cycle of Water Movement
Annual flow of
water on earth in
thousands of km3
Figure from Keller (2000)
1. Evaporation from oceans
2. Precipitation to oceans
3. Transfer of water from atmosphere to land
4. Evaporation from land to atmosphere
5. Precipitation to land
6. Runoff of surface water and groundwater from land to oceans
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Figure from Keller (2000)
Surface runoff plays an important role in the
recycling process. Not only does it replenish lakes,
streams, and groundwater; it also creates the
landscape by eroding topography and transporting
the material elsewhere.
S. Hughes, 2003
Factors Affecting Surface Runoff
Runoff = a function (ƒ) of geology, slope, climate,
precipitation, saturation, soil type, vegetation, and time.
Geology includes rock and soil types and characteristics, as
well as degree of weathering. Porous material (sand, gravel,
and soluble rock) absorbs water far more readily than does
fine-grained, dense clay or unfractured rock.
Well-drained material (porous) has a lower runoff potential,
and therefore has a lower drainage density.
Poorly-drained material (non-porous) has a higher runoff
potential, resulting in greater drainage density.
Drainage density is a measure of the length of channel per
unit area. Many channels per unit area means that more water
is moving off of the surface, rather than soaking into the soil.
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Figure from Keller (2000)
Drainage basins or watersheds have different shapes and
sizes. Large drainage basins are usually divided into smaller
ones. Size and shape have a direct effect on surface runoff.
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DRAINAGE BASINS
Long, narrow drainage basins generally display the most
dramatic effects of surface runoff. They have straight stream
channels and short tributaries.
• Storm waters reach the main channels far more rapidly in long
narrow basins than in other types of basins.
• Flash floods are common in long, narrow drainage basins,
resulting in greater erosion potential.
Topography (relief) and slope (gradient) affect water velocity,
infiltration rate, overland flow rate, and subsurface runoff rates.
Precipitation (type, duration, and intensity) is the key climatic
factor. Infrequent torrential downpours easily erode sedimentladen topography, while soft drizzly rain infiltrates the soil.
Vegetation aids slope stability. Removal of vegetation by fire,
clear-cutting (logging), or animal grazing often results in soil
erosion, adding to the sediment load.
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2
1
3
Figure from Keller (2000)
Throughflow = shallow subsurface flow above the water table
• Requires good infiltration capacity
• Common in humid climates with thick soil layers and good
vegetation cover.
Overland flow occurs when precipitation > infiltration rates.
• Rejected infiltration = due to saturated soil conditions
• Common in semi-arid regions, and in clay-rich soil layers.
Stream Transport
Types of sediment = dissolved load, suspended load, and
bed load.
Dissolved Load: Chemical weathering of rocks produces
ions in solution (examples- Ca2+, Mg+, and HCO3+). High
concentrations of Ca2+ and Mg+ are also known by another
name - hard water.
Suspended Load: Fine sediment, mostly clay and silt,
makes water look cloudy or opaque. The greater the amount
of sediment, the muddier the water.
Bed load: Coarse sediment (silt- to boulder-sized, but
mostly sand and gravel) settles on the bottom of the channel.
Bed load sediment moves by bouncing or rolling along the
bottom. The distance that bed load travels depends on the
velocity of the water.
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Use of Surface Water
Surface water use includes instream and offstream uses.
• Offstream use either removes or diverts the water.
Consumptive use, a form of offstream use, is water used by
industry, irrigation, and households. Eventually, water is
returned to the stream or groundwater system.
• Instream use is not removed or diverted. Examples of
instream use include cooling, navigation, salmon runs, and
fishing.
Desalination is the removal of salt from seawater. It is a very
expensive process (~ 10 times that paid for traditional water
supplies) and is considered a last resort alternative.
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Water Budget for the Conterminous United States
Figure from Keller (2000)
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Instream Water Use
Figure from Keller (2000)
Discharge is the amount of water passing by a particular location
• measured in cubic meters per second (cms)
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Conserving and managing water
Frequently population density and major water supplies do
not coincide. Therefore, water must be transported great
distances to the consumers. California is a good example.
Population density is greatest in the lower 2/3 of California,
south of San Francisco, while water supplies are greatest in
the upper 1/3. Major water diversion projects were
implemented to transport water to densely populated areas.
Los Angeles and Owens Valley (opposite sides of the Sierra
Nevada) are fighting over water rights. This has been an
ongoing problem since the early 1900’s! The LA-Owens
River Aqueduct was constructed, completed in 1913. So
much water has been diverted to LA that the Owens Valley
has suffered from desertification (transformed into a more
desert-like environment). By limiting water diversion,
environmental degradation may be reduced.
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California Aqueducts and Irrigation Canals
• The construction of each
canal or aqueduct represents
diversion of water runoff.
• Many regions that were
once supplied by water from
mountains lost water rights.
• Most water goes to large
cities, such as Los Angeles,
and to large corporations
that produce fruits and
vegetables.
• Much of the land has been
desertified in the process.
Figure from Keller (2000)
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Conserving and managing water
As our population increases, the need for water conservation
and management also increases. An example of river
management is the Colorado River. The Colorado River is the
most regulated river in the U. S. Numerous dams, reservoirs
and canals are "part of" the Colorado River system. The
Colorado basin encompasses parts of Wyoming, Colorado,
Utah, New Mexico, Arizona, California, and Mexico. All want
their fair share of water! Thus, water management is important.
Equally important is water quality. Salinity, a by-product of
water flowing over salt beds, salt springs, and irrigation and
evaporation, increases with distance downstream. A large
desalination plant is under construction on the lower Colorado
River, upstream from the Imperial Dam. After treatment, water
should be of usable quality. Mexico would then be able to use it
for agricultural purposes.
S. Hughes, 2003
The Colorado River Basin
Upper basin
Lower basin
Figure from Keller (2000)
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Colorado River Water (see Table 10.7)
Legal and actual distribution of water:
STATE
California
Arizona
Nevada
Lower Basin
Colorado
Utah
Wyoming
New Mexico
Upper Basin
Mexico
TOTAL
Legal
Entitlement
(106 ac ft/year)
4.400
3.800
0.300
8.500
Actual
Distribution
(106 ac ft/year)
4.400
2.050
0.300
6.750
3.881
1.725
1.050
0.844
7.500
2.406
1.070
0.651
0.523
4.650
1.500
1.500
17.500
14.500
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Wetlands
Not too long ago,
wetlands had a bad
image. Wetlands were
just dank, murky
swamps.
Fortunately, we now realize wetlands have a vital role in our
environment. Wetlands are a natural filter system.
Wetland plants remove toxins from water and sediment.
Freshwater wetlands act as sponges and soak up excess
water, reducing flood conditions.
Coastal wetlands are buffer zones. They reduce the erosion
impact of storms and high waves. Wetlands also provide a
habitat for numerous wildlife and plant species.
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AQUEOUS SOLUTION GEOCHEMISTRY - 1
 Acid = substance containing hydrogen which gives free
hydrogen (H+) when dissolved in water
 Base = substance containing the OH group that yields free
(OH-) when dissolved in water
 An acid solution is one containing an excess of free H+,
and a base is one containing excess of free OH-. A reaction
between an acid and a base is usually called neutralization.
For example:
HCl (acid) + NaOH (base)
H2O + NaCl
which are dissociated into ions:
H+ + Cl- + Na+ + OHH2O + Na+ + Cli.e. Na+ and Cl- are unaffected.
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AQUEOUS SOLUTION GEOCHEMISTRY - 2
 pH = inverse log of the concentration (activity) of free H+
pH = -log [H+]
 Important: Water dissociates into H+ and OH Dissociation constant: Kwater = [H+] [OH-] =10-14
NOTE: There must be 10-7 moles each of H+ and OH- in a kilogram of
neutral solution at standard temperature of 25°C. One mole is 6.023 x
1023 atoms (or molecules) and H2O has a molecular weight of 18 grams
per mole. One kilogram of water has about 1000/18 = 55.6 moles of
water or about 3.35 x 1025 atoms of oxygen. It has about twice that
number (6.7 x 1025 atoms) of H+ (the amount of free H+ or free OH- is
relatively small compared to the amount of undissociated H2O).
 pH ranges at 25°C from 0 to 14; pH < 7 = acidic solution; pH > 7 =
basic solution. If and acid such as HCl is added then pH decreases; if a
base such as NaOH is added then pH increases.
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AQUEOUS SOLUTION GEOCHEMISTRY - 3
 pH increases as carbonic acid (a weak acid) dissociates: When
carbon dioxide combines with water, such as what happens in
the atmosphere when fossil fuels are burned, carbonic acid is
formed: H2O + CO2
H2CO3. Free H+ are made available
during successive dissociations:
 H2CO3
H+ + HCO3- carbonic acid to bicarbonate
occurs at pH ~6.4
 HCO3
H+ + CO32- bicarbonate to carbonate
occurs at pH ~10.3
Remember, free H+ is available only when acidic, or when pH <
~7. The dissociation of bicarbonate to carbonate occurs when
there is too much OH- in the system and H+ is "released" to
balance out the base.
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AQUEOUS SOLUTION GEOCHEMISTRY - 4
 Cations = electron donors, positive charge: Na+, K+, Mg++,
Ca++, Fe++ or Fe+++, Mn++, Al+++
 Anions = electron acceptors, negative charge: Cl-, F-, I-, Br-,
SO4--, CO3--, HCO3-, NO3--, NO2 Metals = act like cations mostly: Cu, Zn, Pb, Co, Ni, Cr, As, Se,
Mo, etc.
Water Analyses - Need to have cation-anion balance
millequivalent (MEQ) = mole equivalent charge or anion or
cation, measure of total charge due to the ion dissolved in the
solution: MEQ = XX mg/L / MW x CHG
Example: NaCl in solution, Na = 50 mg/L (50 ppm): 50/23 x 1 =
2.17 MEQ; and Cl = 77 mg/L (77 ppm): 77/35.5 x -1 = -2.17 MEQ
So, if the total cation and anion MEQ’s are not balanced, some
error exists in the analysis.
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WATER (surface and ground water)
TERMS
FOR
UNDERSTANDING
• antecedent water • irrigation ion
• aquifer
• juvenile water
• artesian well
• overdraft
• base flow
• overland flow
• bed load
• meteoric water
• capillary fringe
• precipitation
• climate
• runoff
• cone of depression• saturation
• connate water
• slope
• drainage basin
• suspended load
• drainage density • topography
• dissolved load
• transpiration
• erosion
• throughflow
• evaporation
• vadose zone
• groundwater
• water quality
• hydrologic cycle • water table
• infiltration
• watershed
• irrigation ion
• wetland S. Hughes, 2003