GROUNDWATER
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GROUNDWATER Im perm eable rock G round w ater Saltw ater Stream channel O cean Land surface Vadose zone W et-season w atertable D ry-season w atertable Well C apillary fringe Infiltration orseepage recharge (unsat.flow ) G round w ater(sat.flow ) Phreatic zone
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GROUNDWATER. GROUNDWATER. GROUNDWATER. Aquifer “Geologic unit that can store and transmit enough water to be a significant water resource” 1. Large volume (in relation to the amounts being removed annually) 2. Moderately high porosity 3. Facilitate easy movement of water toward a well - PowerPoint PPT Presentation
Transcript of GROUNDWATER
GROUNDWATER
Impermeable rock
Ground water
Salt water
Stream channel
Ocean
Land surface
Vadose zone
Wet-season water tableDry-season water table
Well
Capillary fringe
Infiltration or seepage recharge (unsat. flow) Ground water (sat. flow)
Phreatic zone
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655.5
656
656.5
657
657.5
658
658.5
0 50 100 150 200 250 300 350 400
Days
Ele
vati
on
(m
sl)
Ground surface
O D F A J A
Large seriesof storms
Cold dry
Series ofsmall storms
Snow
Midwinter melt
Snow
Spring melt
Summer
Large storm
GROUNDWATER
Aquifer “Geologic unit that can store and transmit enough
water to be a significant water resource” 1. Large volume (in relation to the amounts being
removed annually) 2. Moderately high porosity 3. Facilitate easy movement of water toward a well aquiclude
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Confined versus unconfined
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Elevation energy and pressure energy
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Elevation energy and pressure energy
WellWell
WellA
BC
Water level
Sea level
h
he
p hp h
p
he h
e
hp
he
Well and screen
Flow
= pressure head
= elevation head
SandstoneShale
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Potentiometric surface
Equipotential lines
Potentiometric contours
Clay
Clay
potentiometric surface
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Datum
Q
Q
h1h2
p1
p2
z2z1
dh
dx
A
1
2
elev
atio
n he
ad
tota
l he
ad
Vx = Q/A
Water potential (hydraulic) gradient: Q = h/d
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Datum
Q
Q
h1h2
p1
p2
z2z1
dh
dx
A
1
2
elev
atio
n he
ad
tota
l he
ad
Q = A h/d Q = K A (h/d) Hydraulic conductivity (K) “Permeability” T = Kb where b = aquifer thickness
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Storage properties of aquifers
In GW flow, S = 1 and volume stored/unit volume =
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The volume of water a unit volume of aquifer releases in response to h =
Specific storage, Ss
Volume water released [L3]
Ss =
Volume of aquifer [L3] x h [L]
Storage coefficient or storativity, S Volume water released [L3] S =
Surface area of aquifer [L2] x h [L]
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S and Ss are related as
S = bSs
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Unconfined aquifer: Specific yield (Sy) = sy
= volume of stored GW released per unit surface area per unit decline of
S = sy
sy = bSs
and Ss = sy b
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= Sy + Sr
Fc
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