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8/17/2019 04 Aquifer Characteristics
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ESS 454
HydrogeologyModule 2
• Properties of Materials
• Basic Physics
•
Darcy’s Law• Characteristics of
!uifers
• Elasticity a"d Storage
#"structor$ MichaelBrow"%row"&ess'washi"gto"'
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Characteristics of!uifers
Lear"i"g (%)ecti*es• +ater ta%le$ – De,"e a"d #llustrate e-a.ples of a!uifers
– /"dersta"d the relatio"ship %etwee" 0owdirectio"s a"d geo.etry of the surface• #f 0at 1 "o 0ow
• Slopi"g 1 0ow i" dow"1hill directio"
• Discharge at lowest poi"t
• !uifer – /"dersta"d that it is a geologic u"it capa%le
of stori"g a"d tra"s.itti"g water to wells•
3"ow that per.ea%ility of a!uifer .aterials istypically 12 Darcy
• Co","i"g layers$• /"dersta"d de,"itio"s of a!uitards6 a!uifuge6 a"d
lea7y co","i"g layer
• 3"ow that per.ea%ility of co","i"g layers is
typically 8 12
Darcy
3'5i"ches9day
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• /"dersta"d the di:ere"ce %etwee"/"co","ed a"d Co","ed a!uifers
• 3"ow what a" rtesia" a!uifer a"d a
Perched a!uifer are – Be a%le to draw represe"tati*e cross sectio"s to
illustrate
• Pote"tio.etric Surfaces – 3"ow what is .ea"t %y a ;scree"ed well<
– Be a%le to illustrate a co","ed a!uifer with a
collectio" of wells scree"ed at a co..o" depth – Be a%le to co"tour Head =ele*atio" of water i"
each well> to illustrate the ;Pote"tio.etricSurface<
– Be a%le to deter.i"e the .ag"itude a"ddirectio" of the gradie"t of the Pote"tio.etricsurface a"d correctly deter.i"e the directio" ofwater 0ow'
• Be a%le to co""ect a!uifer properties=?ra"s.isi*ity a"d Storati*ity> withproperties of geologic .aterials =36 Sy6
co.pressi%ility>
•
/"dersta"d the sig"i,ca"ce ofHo.oge"eity a"d "isotropy
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+ater ?a%le
@adose oru"saturated
Ao"e
Saturated Ao"e
+ater ?a%le
Capillaryri"ge
scree"
/"co","ed
HoriAo"tal water ta%le "o0ow
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∆h
∆l
low
Directio"
rou"dwater 0ows i"
directio" ofdecreasi"g hydraulichead
Hydraulic gradie"t ∆h9∆l
+ater ?a%le
/"co","ed
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Surface de,"ed %y locatio"of water ta%le is the;Pote"tio.etric Surface<
radie"t of hydraulichead is i" ;uphill<directio"
Ca" .ap hydraulicheadas co"tour plot
dh9dl
0o
w
+ater ?a%le
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+ater ?a%le
• #" a%se"ce of 0ow6 water ta%le is 0at
– Slopi"g water ta%le i.plies 0ow
•
?he water ta%le has the ge"eralshape as the surface topography
• rou"dwater 0ow is usually fro.topographic highs to topographiclows
• rou"dwater discharges at
topographic low spots
• echarge %y
– #",ltratio"
– Lateral or *ertical 0ow fro. othera!uifers
So.e Hu.id Cli.atee"eralities
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!uifers; geologic u"it capa%le of stori"g a"d tra"s.itti"g
water to wells
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!uifersco","ed
*ariety of geologic situatio"s gi*e rise to layers ha*i"g di:ere"t hydraulico"ducti*ities
co","i"glayers
a!uifers
echarge regio"
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!uifers
?ra"sitio" fro. /"co","ed to;artesia"< to ;0owi"g< a!uifer
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!uifers
;Perched$ a!uifer a"d ge"eratio" of;spri"gs<
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!uifer Characteristics
• ?ra"s.isi*ity F ?
? % G 3% is a!uifer thic7"ess6 S# u"its of .29s
for horiAo"tal 0ow ? is su. of ?’s forall layers
• Storati*ity F Sor a *olu.e of water @w ge"erated fro. a" area ;< for a drop i"
hydraulic head of ∆h
@w S ∆h
e.e.%er that geologic .aterials werecharacteriAed %y their ;hydraulic Co"ducti*ity< =3>a"d their ;Speci,c ield< =Sy>
*olu.e
S is di.e"sio"lessI 8
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Ho.oge"eity a"d #sotropy
• Ho.oge"eous$ property is the sa.e i" all locatio"s
• #sotropic$ property is the sa.e whe" .easured i"
e*ery directio"
• !uifers are ge"erally ;#"ho.oge"eous< a"d;"isotropic<
egio"s oflower 3
Joi"ts withhigher 3
But i" #g"ora"cethis is fre!ue"tlyo*erloo7ed
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"isotropy
• largest di:ere"ce i" Hydraulic Co"ducti*ity .aye-ist %etwee" the horiAo"tal a"d *erticaldirectio"s
– or horiAo"tal 0ow$ 3 su. =3 h.%.>9%
– or *ertical 0ow$ 3 % 9su.=%.93 *.>
• 3 is a ;te"sor property< – #f 3 is scalar =isotropic> 0ow is i" directio" of head
gradie"t – #f 3 is te"sor =a"isotropic>6 0ow is "ot parallel to gradie"t
• low ca" %e deter.i"ed fro. li"ear alge%ra
• +ill !ua"titati*ely de*elop this idea later
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Co.i"g /p$Speci,c Storage
• Elasticity$ water a"d roc7 are elastic
– Hoo7e’s Law$ d-9- α dσ
• E:ecti*e Stress$ – σ ? σe K P =total stress is supported %y roc7 a"d
%y 0uid>
– dσ ? dσe K dP =if σ ? is co"sta"t dP 1dσe>
• Speci,c Storage =Ss> ρwaterg =α K "β>
– /"its of 9L
– Storati*ity S % Ss =di.e"sio"less>
Pre*iew of i.porta"t co"cepts