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DAY ONE
Chapter 11
Water
Section 1: Water Resources
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Water Resources Water is essentialto life on Earth. Humans
can live for more than month without food, but
we can live for onl a few das without water.
!wo "inds of water found on Earth:
Fresh water, the water that people candrin", contains little salt.
Salt water, the water in oceans, contains
a hi#her concentration of dissolved salts.
$ost human uses for water, such as drin"in#
and a#riculture, re%uire fresh water.
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The Water Cycle Water is a renewable resource because it is
circulated in the water ccle.
&n the water ccle, water molecules travel
between the Earth's surface and the
atos!here.
( Water e"a!oratesat the Earth's surface. Water vapor rises into the air.
( )s the vapor rises, it condensesto form
clouds. Eventuall the water in clouds
falls bac" to the Earth.
!he oceans are important because alost
all of the Earth's water is in the ocean.
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#ill Nye $ Water Cycle
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The Water Cycle
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%lobal Water Distribution
)lthou#h &1percent of the Earth's
surface is covered with water, nearl
'&percent of Earth's water is salt
waterin oceans and seas.
*f the fresh water on Earth, about
&&percent is fro(enin #laciers and
polar icecaps.
*nl a small percenta#e of the wateron Earth is li%uid fresh water that
humans can use.
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%lobal Water Distribution
!he fresh water we use comes mainl from la)es and
ri"ersand from a relativel narrow +one beneath the
Earth's surface.
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Surface Water
Surface wateris all the bodies of freshwater, salt water, ice, and snow, that are
found above the #round.
!he distribution of surface water has plaed
a vital role in the de"elo!entof human
societies.
!hrou#hout histor, people have built cities
and farms near reliable sources of water.
!oda, most lar#e cities depend on surface
water for drin"in# water, water to #row crops,
food such as fish, power for industr, and
transportation.
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Ri"er Systes Streams form as water from fallin# rain
and meltin# snow drains from mountains,hills, plateaus, and plains.
)s streams flow downhill, the combine
with other streams and form ri"ers.
) ri"er syste is a flowin# networ" ofrivers and streams drainin# a river basin.
!he Aa(on Ri"ersstem is the lar#est
river sstem in the world as it drains an
area of land that is nearl the si+e ofEurope.
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Watersheds
) watershedis the area of land that is
drained b a water sstem.
!he amount of water that enters a
watershed varies throu#hout the ear.
Rapidl meltin# snow as well as sprin#
and summer rains can dramaticall
increasethe amount of water in a
watershed.
)t other times of the ear, the river sstemthat drains a watershed ma be reduced
to a tric"le.
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Watersheds
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%roundwater $ost of the fresh water that is available
for human use cannotbe seen, as it
eists under#round.
When it rains, some of the water that
falls onto the land flows into la"es and
streams.
-ut much of the water percolates
throu#h the soil and down into the
roc"s beneath.
%roundwateris the water that is
beneath the Earth's surface.
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%roundwater
)s water travels beneath the Earth's surface, it eventuall
reaches a level where the roc"s and soil are saturated with
water.
( !his level is "nown as the water table.
&n wet re#ions, the water table ma be at the Earth'ssurface.
( &n deserts, the water table ma be hundreds of meters
beneath Earth's surface.
!he water table has !ea)s and "alleys that match the
shape of the land above. roundwater tends to flow slowl
from the pea"s to the valles.
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%roundWater *ideo
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A+uifers
)n a+uiferis a bod or roc" or sediment thatstores #roundwater and allows the flow of
#roundwater.
!he are an i!ortantwater source for man
cities.
!he water table forms the u!!er boundaryof an
a%uifer, and most a%uifers consist of materials
such as roc), sand, and -ra"elthat have a lot of
spaces where water can accumulate.
roundwater can also dissol"eroc" formations,fillin# vast caves with water, creatin# under#round
la"es.
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.orosity
.orosityis the percenta#e of
the total volume of a roc" or
sediment that consists of open
spaces.
Water in an a%uifer is stored in
the pore spaces and flows form
one pore space to another.
!he more porous a roc" is, themore water it can hold.
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.ereability
.ereabilityis the abilit of a roc" or sediment to let
fluids pass throu#h it open spaces or pores.
$aterials such as -ra"elthat allow the flow of water are
permeable. $aterials such as cla or #ranite that stop
the flow of water are impermeable.
!he most productive a%uifers usuall form in permeable
materials, such as sandstone, liestone, or layers of
sand and -ra"el.
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The Rechar-e /one !o reach an a%uifer, surface water must
travel down throu#h permeable laers ofsoil and roc".
Water cannot reach an a%uifer from places
where the a%uifer is covered b
impermeable materials.
!he rechar-e (oneis an area in which
water travels downward to become part of
an a%uifer.
Rechar#e +ones are environmentall
sensitive areas because an pollution inthe rechar#e +one can also enter the
a%uifer.
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The Rechar-e /one
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The Rechar-e /one
!he si+e of an a%uifer's rechar#e +one is affected b the!ereabilityof the surface above the a%uifer.
Structures such as buildin-s and !ar)in- lots can act
as impermeable laers and reduce the amount of water
enterin# an a%uifer.
Communities should carefull mana#e rechar#e +ones,
because surface water can ta"e a ver lon# time to refill
an a%uifer, even tens of thousands of ears.
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Wells
) hole that is du- or drilled toreach #roundwater is called a well.
Humans have du# wells to reach
#roundwater for thousands of ears.
We di# wells because #round water
ma be a more reliable source of
water than surface water and
because water is filtered andpurified as it travels under#round.
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!he hei#ht of the water table chan#es seasonall, sowells are drilled to e0tendbelow the water table.
&f the water tables falls below the bottom of the welldurin# a drou#ht, the well will dr up.
&n addition, if #roundwater is removed faster than it isrechar#ed, the water table ma fall below the bottom of awell.
!o continue supplin# water, the well must be drilleddeeper.
Wells
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Tic)et out the Door
1. What is the difference between fresh and salt water/
0. What is the percenta#e of Earth that is covered with
water/
. What is a river sstem/
2. What is #roundwater/
3. What is an a%uifer/
4. What is the difference between permeabilit and
porosit/