04 Aquifer Characteristics

8/17/2019 04 Aquifer Characteristics

1/15

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"'


2/15

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


3/15

• /"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


4/15

+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


5/15

∆h

∆l

low

Directio"

rou"dwater 0ows i"

directio" ofdecreasi"g hydraulichead

Hydraulic gradie"t ∆h9∆l

+ater ?a%le

/"co","ed


6/15

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


7/15

+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


8/15

!uifers; geologic u"it capa%le of stori"g a"d tra"s.itti"g

water to wells


9/15

!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"


10/15

!uifers

?ra"sitio" fro. /"co","ed to;artesia"< to ;0owi"g< a!uifer


11/15

!uifers

;Perched$ a!uifer a"d ge"eratio" of;spri"gs<


12/15

!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


13/15

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


14/15

"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


15/15

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

04 Aquifer Characteristics

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