Chapter 9 Water Resources

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Chapter 9 Water Resources
Geosystems 5e An Introduction to Physical
Geography

Robert W. Christopherson Charlie Thomsen
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Web URL for GEOG 123b

• http//instruct.uwo.ca/geog/123b/
• -Assignment 2 can be printed from that location.

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Note about previous discussion about Global
Warming Global Dimming

• Scientists are now discovering that the amount of
  solar energy reaching the Earth's surface has
  been gradually falling in the last few decades.
  Paradoxically, the decline in sunlight may mean
  that global warming is a far greater threat to
  society than previously thought.
• Dimming appears to be caused by air pollution.
  Burning coal, oil and wood, whether in cars,
  power stations or cooking fires, produces not
  only invisible carbon dioxide - the principal
  greenhouse gas responsible for global warming -
  but also tiny airborne particles of soot, ash,
  sulfur compounds and other pollutants.
• Because the particles seed the formation of water
  droplets, polluted clouds contain a larger number
  of droplets than unpolluted clouds. Recent
  research shows that this makes them more
  reflective than they would otherwise be,
  reflecting the Sun's rays back into space.
• But perhaps the most alarming aspect of global
  dimming is that it may have led scientists to
  underestimate the true power of the greenhouse
  effect. They know how much extra energy is being
  trapped in the Earth's atmosphere by the extra
  carbon dioxide we have placed there. What has
  been surprising is that this extra energy has so
  far resulted in a temperature rise of just 0.6
  degree Celsius. This has led many scientists to
  conclude that the present-day climate is less
  sensitive to the effects of carbon dioxide than
  it was, say, during the ice age, when a similar
  rise in CO2 led to a temperature rise of six
  degrees Celsius.
• But it now appears the warming from greenhouse
  gases has been offset by a strong cooling effect
  from dimming - in effect two of our pollutants
  have been canceling each other out. This means
  that the climate may in fact be more sensitive to
  the greenhouse effect than previously thought.

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Lecture overview

• In this lecture we will examine the Earths
  plumbing systemthe hydrologic cycle. The text
  (Chapter 9) focuses in on the soil-moisture
  environment and the application of the hydrologic
  cycle to a specific site. Also, the water
  balance, which is an accounting of the hydrologic
  cycle for a specific area with emphasis on plants
  and soil moisture follows.
• We will also review the nature of groundwater and
  look at several examples of this generally abused
  resource. Groundwater resources are closely tied
  to surface-water budgets. We will also consider
  the daily water we withdraw and consume from
  available resources, in terms of both quantity
  and quality.

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Some basic stats

• Fortunately, water is a renewable resource,
  constantly cycling through the environment,
  endlessly renewed. Even so, some 80 countries
  face impending water shortages, either in
  quantity or quality, or both. One billion people
  lack access to safe water in 2001 some 1.8
  billion lack adequate sanitary facilities. During
  the first half of the new century water
  availability per person will drop by 74, as
  population increases and adequate quality water
  decreases.

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After this lecture and reading the chapter you
should be able to

• Illustrate the hydrologic cycle with a simple
  sketch and label it with definitions for each
  water pathway.
• Relate the importance of the water-budget concept
  to your understanding of the hydrologic cycle,
  water resources, and soil moisture for a specific
  location.
• Construct the water-balance equation as a way of
  accounting for the expenditures of water supply
  and define each of the components in the equation
  and their specific operation.
• Describe the nature of groundwater and define the
  elements of the groundwater environment.
• Identify critical aspects of freshwater supplies
  for the future and cite specific issues related
  to sectors of use, regions and countries, and
  potential remedies for any shortfalls.

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1. Explaining a simplified model of the complex
flows of water on Earththe hydrologic cycle.

• Vast currents of water, water vapor, ice, and
  energy are flowing about us continuously in an
  elaborate open global plumbing system. A
  simplified model of this complex system is useful
  to our study of the hydrologic cycle (Figure
  9-1). The ocean provides a starting point, where
  more than 97 of all water is located and most
  evaporation and precipitation occur.

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Hydrologic Cycle Model The model shows how water
travels endlessly through the hydrosphere,
atmosphere, lithosphere, and biosphere. The
triangles show global average values as
percentages. Note that all evaporation equals
all precipitation when all of the Earth is
considered. Regionally, various parts of the
cycle will vary, creating imbalances and,
depending on climate, surpluses in one region and
shortages in another.
Figure 9.1
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Hydrologic cycle Contd

• If we assume that mean annual global evaporation
  equals 100 units, we can trace 86 of them to the
  ocean. The other 14 units come from the land,
  including water moving from the soil into plant
  roots and passing through their leaves. Of the
  ocean's evaporated 86 units, 66 combine with 12
  advected (transported) from the land to produce
  the 78 units of precipitation that fall back into
  the ocean. The remaining 20 units of moisture
  evaporated from the ocean, plus 2 units of
  land-derived moisture, produce the 22 units of
  precipitation that fall over land. Clearly, the
  bulk of continental precipitation derives from
  the oceanic portion of the cycle.

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Question What are the possible routes that a
raindrop may take on its way to and into the soil
surface?

• Answer Precipitation that reaches Earth's
  surface follows a variety of pathways. The
  process of precipitation striking vegetation or
  other groundcover is called interception.
  Precipitation that falls directly to the ground,
  coupled with drips onto the ground from
  vegetation, constitutes throughfall. Intercepted
  water that drains across plant leaves and down
  plant stems is termed stem flow and can represent
  an important moisture route to the surface.
  Water reaches the subsurface through
  infiltration, or penetration of the soil surface.
  It then permeates soil or rock through vertical
  movement called percolation (Figure 9.3).

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Fig. 9.3 The soil-moisture environment
Precipitation supplies the soil-moisture
environment. The principal pathways for water
include interception by plants throughfall to
the ground collection on the surface, forming
overland flow to streams transpiration (water
moving from the soil into plant roots and passing
through their leaves) and evaporation from plant
evaporation from land and water and
gravitational water moving to subsurface
groundwater. Water moves from the surface into
the soil by infiltration and percolation.
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How do precipitation and evaporation volumes from
the ocean compare with those over land?

• More than 97 of Earth's water is in the ocean,
  and here most evaporation and precipitation
  occur. 86 of all evaporation can be traced to
  the ocean. The other 14 comes from the land,
  including water moving from the soil into plant
  roots and passing through their leaves by
  transpiration. Of the ocean's evaporated 86, 66
  combines with 12 advected from the land to
  produce the 78 of all precipitation that falls
  back into the ocean. The remaining 20 of
  moisture evaporated from the ocean, plus 2 of
  land-derived moisture, produces the 22 of all
  precipitation that falls over land.

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How might an understanding of the hydrologic
cycle in a particular locale, or a soil-moisture
budget of a site, assist you in assessing water
resources? Some specific examples.

• A soil-moisture budget can be established for any
  area of Earth's surface by measuring the
  precipitation input and its distribution to
  satisfy the "demands" of plants, evaporation, and
  soil moisture storage in the area considered. A
  budget can be constructed for any time frame,
  from minutes to years. See Figures 9-11 in next
  slide.

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• Figure 9.11 Sample water budget. Annual
  average water-balance components graphed for
  Kingsport, Tennessee. The comparison of plots
  for precipitation inputs (PERCIP), and potential
  evapotranspiration outputs (POTET) determines the
  condition of the soil-moisture environment. A
  typical pattern of spring surplus, summer
  soil-moisture utilization, a small summer
  deficit, autumn soil-moisture recharge, and
  ending surplus highlights the year.

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What does The soil-water budget is an assessment
of the hydrologic cycle at a specific site
means?

• A water balance can be established for any area
  of Earth's surface by calculating the total
  precipitation input and the total of various
  outputs. The water-balance approach allows an
  examination of the hydrologic cycle, including
  estimation of streamflow at a specific site or
  area, for any period of time. The purpose of the
  water balance is to describe the various ways in
  which the water supply is expended. The water
  balance is a method by which we can account for
  the hydrologic cycle of a specific area, with
  emphasis on plants and soil moisture.

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What are the components of the water-balance
equation? (Fig. 9.4)
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Explain how to derive actual evapotranspiration
(ACTET) in the water-balance equation.

• The actual amount of evaporation and
  transpiration that occurs is derived by
  subtracting DEFIC, or water demand, from POTET.
  Under ideal conditions, POTET and ACTET are about
  the same, so that plants do not experience a
  water shortage. Droughts result from deficit
  conditions, where ACTET is greater than the
  available moisture.

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What is potential evapotranspiration (POTET)? How
do we go about estimating this potential rate?

• POTET is the amount of moisture that would
  evaporate and transpire if the moisture were
  available the amount lost under optimum moisture
  conditionsthe moisture demand. Both evaporation
  and transpiration directly respond to climatic
  conditions of temperature and humidity. For the
  empirical measurement of POTET, probably the
  easiest method employs an evaporation pan, or
  evaporimeter. As evaporation occurs, water in
  measured amounts is automatically replaced in the
  pan. Screens of various sized mesh are used to
  protect against overmeasurements created by wind.
  A lysimeter is a relatively elaborate device for
  measuring POTET, for an actual portion of a field
  is isolated so that the moisture moving through
  it can be measured. See next slide (Figure 9-7)
  for a sketch of such a device.

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• Fig 9.7 Lysimeter
• Drawn is a weighing lysimeter for measuring
  evaporation and transpiration. The various
  pathways of water are tracked Some water remains
  as soil moisture, some is incorporated into plant
  tissues, some drains from the bottom of the
  lysimeter, and the remainder is credited to
  evapotranspiration. Given natural conditions,
  the lysimeter measures actual evapotranspiration.

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Explaining the operation of soil-moisture
storage, soil-moisture utilization, and
soil-moisture recharge.

• Soil moisture storage (?STRGE) refers to the
  amount of water that is stored in the soil and is
  accessible to plant roots, or the effective
  rooting depth of plants in a specific soil. This
  water is held in the soil against the pull of
  gravity. Soil is said to be at the wilting point
  when plant roots are unable to extract water in
  other words, plants will wilt and eventually die
  after prolonged moisture deficit stress.
• The soil moisture that is generally accessible to
  plant roots is capillary water, held in the soil
  by surface tension and cohesive forces between
  the water and the soil. Almost all capillary
  water is available water in soil moisture storage
  and is removable for POTET demands through the
  action of plant roots and surface evaporation
  some capillary water remains adhered to soil
  particles along with hygroscopic water. When
  capillary water is full in a particular soil,
  that soil is said to be at field capacity, an
  amount determined by actual soil surveys.

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Contd

• When soil moisture is at field capacity, plant
  roots are able to obtain water with less effort,
  and water is thus rapidly available to them. As
  the soil water is reduced by soil moisture
  utilization, the plants must exert greater effort
  to extract the same amount of moisture. Whether
  naturally occurring or artificially applied,
  water infiltrates soil and replenishes available
  water content, a process known as soil moisture
  recharge.

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Example (Fig. 9.10) In the case of silt-loam
soil from, roughly what is the available water
capacity? How is this value derived?

• The lower line on the graph plots the wilting
  point the upper line plots field capacity. The
  space between the two lines represents the amount
  of water available to plants given varying soil
  textures. Different plant types growing in
  various types of soil send roots to different
  depths and therefore are exposed to varying
  amounts of soil moisture. For example,
  shallow-rooted crops such as spinach, beans, and
  carrots send roots down 65 cm (25 in.) in a silt
  loam, whereas deep-rooted crops such as alfalfa
  and shrubs exceed a depth of 125 cm (50 in.) in
  such a soil. A soil blend that maximizes
  available water is best for supplying plant water
  needs.

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Example Water balance and water management
scheme in Snowy Mountain, Southeastern Australia.

• In the Snowy Mountains, part of the Great
  Dividing Range in extreme southeastern Australia,
  precipitation ranges from 100 to 200 cm (40 to 80
  in.) a year, whereas interior Australia receives
  under 50 cm (20 in.), and drops to less than 25
  cm (10 in.) further inland. POTET (potential
  evapotranspiration) values are high throughout
  the Australian outback and lower in the higher
  elevations of the Snowy Mountains.
• The plan was designed to take surplus water that
  flowed down the Snowy River eastward to the
  Tasman Sea and reverse the flow to support newly
  irrigated farmland in the interior of New South
  Wales and Victoria. The westward flow of the
  Murray, Tumut, and Murrumbidgee rivers is
  augmented, and as a result, new acreage is now in
  production in what was dry outback, formerly
  served only by wells drawing on meager
  groundwater supplies.
• In the 1990s the Scheme passed its 50th
  anniversary of operation, a major milestone.

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Are groundwater resources independent of surface
supplies, or are the two interrelated? (Movie at
the end of lecture)

• Groundwater is the part of the hydrologic cycle
  that lies beneath the ground and is therefore
  tied to surface supplies. Groundwater is the
  largest potential source of freshwater in the
  hydrologic cyclelarger than all surface
  reservoirs, lakes, rivers, and streams combined.
  Between Earth's surface and a depth of 3 km
  (10,000 ft) worldwide, some 8,340,000 km3
  (2,000,000 mi3) of water resides. (See next
  slide).

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Fig. 9.15 Groundwater resource potential for the
United States and Canada. Highlighted areas of
the United states are underlain by productive
aquifers capable of yielding freshwater to wells
at 0.2 m3/per minute or more- for Canada the
figure is 0.4 liters per second.
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At what point does groundwater utilization become
groundwater mining?

• Aquifers frequently are pumped beyond their flow
  and recharge capacities groundwater mining
  refers to this overutilization of groundwater
  resources. Large tracts of the Midwest, West,
  lower Mississippi Valley, and Florida experience
  chronic groundwater overdrafts. In many places
  the water table or artesian water level has
  declined more than 12 m (40 ft). Groundwater
  mining is of special concern today in the High
  Plains aquifer.

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What is the nature of groundwater pollution? Can
contaminated groundwater be cleaned up easily?

• When surface water is polluted, groundwater also
  becomes contaminated because it is fed and
  recharged from surface water supplies.
  Groundwater migrates very slowly compared with
  surface water. Surface water flows rapidly and
  flushes pollution downstream, but sluggish
  groundwater, once contaminated, remains polluted
  virtually forever. Pollution can enter
  groundwater from industrial injection wells,
  septic tank outflows, seepage from
  hazardous-waste disposal sites, industrial
  toxic-waste dumps, residues of agricultural
  pesticides, herbicides, fertilizers, and
  residential and urban wastes in landfills. Thus,
  pollution can come either from a point source or
  from a large general area (a non-point source),
  and it can spread over a great distance. Because
  surface water flows rapidly, it can flush
  pollution downstream. Yet, if groundwater is
  polluted, because it is slow moving, once its
  contaminated, it will remain polluted virtually
  forever.

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Water Scarcity

• Water Sustainability Issues

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World Water Day, March 22, 2003
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Water Consumption

• 1.3 gallons/day needed to survive, on average
• 13 gallons/day needed for drinking, cooking,
  bathing, and sanitation
• U.S. 65-78 gallons/day for drinking, cooking,
  bathing and lawn watering
• Somalia 2.3 gallons/day

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http//water.usgs.gov/watuse/graphics/wuto.fact.3d
.gif
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Summary Why the interest?

• 1.2 billion people lack clean drinking water
• 250 million cases of water-related disease/year,
  with 5 10 million deaths
• Over last 100 years, nearly ½ of all wetlands
  lost
• Water pollution growing problem (50 people in
  developing countries have polluted water sources)

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End of Chapter 9
Geosystems 5e An Introduction to Physical
Geography

Robert W. Christopherson Charlie Thomsen
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Movie

• Groundwater Approximately three-quarters of
  Earths surface is covered by water. But most
  fresh water comes from underground. Topics of
  this program include aquifers, rock porosity and
  permeability, artesian wells, the water table,
  cave formation, sinkholes, and how groundwater
  may become contaminated.