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7/30/2019 Top 11 Water Cycle (Part 2)
http://slidepdf.com/reader/full/top-11-water-cycle-part-2 1/15
CHEM115 Environmental Chemistry
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CHAPTER 11
(part 2)
HYDROLOGIC CYCLE
7/30/2019 Top 11 Water Cycle (Part 2)
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CHEM115 Environmental Chemistry
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Water Cycle
Only about 0.001% of the total water on earth is
in the atmosphere anytime.
Around 85% of all water that enters the
atmosphere is derived from the ocean.
More than 99% of earth’s water in its natural state
is unavailable for beneficial human use.
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CHEM115 Environmental Chemistry
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Where is water found?
Location % of water Avg. Residence time
Oceans 97.20 thousands of year
Ice caps and glaciers 2.15thousands of years andlonger
Atmosphere 0.0010 9 day
Fresh water lakes 0.0009 tens of years
Groundwater (to depthof 0.8km) 0.31
hundreds to thousands of years
Rivers and streams 0.0001 2 weeks
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CHEM115 Environmental Chemistry
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Hydrologic Cycle
Cloud formation
Rain clouds
Precipitation
Infiltration
Percolation
Groundwater Rock
Soil
Ocean
To ocean
Surface runoff
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Hydrological Cycle
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Source: http://oceanworld.tamu.edu/resources/oceanography-book/Images/water-cycle.jpg
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Hydrological Cycle
Circurlation and conservation of earth’s water as itcirculates from the land to the sky and back again is
called the ‘hydrological cycle’ or ‘water cycle’.
The stages of the cycle are:
• Evaporation
• Transport
• Condensation
• Precipitation
• Groundwater
• Run-off CHEM115 Environmental Chemistry
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7/30/2019 Top 11 Water Cycle (Part 2)
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Hydrological CycleEvaporation
• Process by which water changes from a liquid to a gas.
The sun’s heat provides energy to evaporate water from
the earth’s surface. Land, lakes, rivers and oceans send
up a steady stream of water vapour and plants also lose water to the air (transpiration).
• Approximately 80% - oceans
20% - inland water and vegetation.
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7/30/2019 Top 11 Water Cycle (Part 2)
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Transport• The movement of water through the
atmosphere, specifically from over the oceans to
over land.• Some of the earth’s moisture transport is visible as
clouds, which themselves consist of ice crystals and/or
tiny water droplets.
• Most water is transported in the form of water vapour, which is actually the third most abundant gas in the
atmosphere. CHEM115 Environmental Chemistry
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Hydrological Cycle
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Condensation• The transported water vapour
eventually condenses , forming tiny droplets in
clouds.
Precipitation
• Primary mechanism for transporting water fromthe atmosphere to the surface of the earth.
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Hydrological Cycle
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Hydrological CycleGroundwater
• Some of the precipitation soaks into the ground and
this is the main source of the formation of the waters
found on land - rivers, lakes, groundwater and glaciers.
• Some of the underground water is trapped betweenrock or clay layers.
• Under special circumstances, groundwater can even
flow upward in artesian wells. The flow of groundwater
is much slower than run-off with speeds usually
measured in centimetres per day, metres per year or
even centimetres per year.CHEM115 Environmental Chemistry
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Hydrological CycleRun-off
• Most of the water which returns to land flows
downhill.
• Different surfaces hold different amounts of
water and absorb water at different rates. As a
surface becomes less permeable, an increasing
amount of water remains on the surface,
creating a greater potential for flooding .
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Evaporation and transpiration are important inhydrologic cycle.
Evaporation of water reduces the temperature.Condensation is exothermic and increase temp
at the air/water interface.
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Water infiltrating the ground will either reach water table or be taken up by plants.
Though water is trapped as glaciers or ice caps in
cold regions for thousand years, eventually it
returns to hydrologic cycle when ice caps andglaciers melt.
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Bonus (0.5)
Briefly describe the evaporation process inhydrological cycle.
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