Ground Water Basicscontinued

Soil Moisture Regimes• Aridic arid climate, usually dry, irrigation required for crop

production.• Ustic—semiarid climate, rainfall during a growing season. • Xeric—semiarid climate, Mediterranean climate, cool, moist winters,

dry summers,• dryland crop possible from stored soil water. • Udic—humid climate, usually moist, generally irrigation not required

for crop• production. • Perudic—precipitation exceeds evapotranspiration in all months, but

soil is not• saturated for long periods.• Aquic—soil saturated long enough to cause anaerobic conditions

Soil Moisture Regimes

Types of Porous Media

Homogeneous Heterogeneous

Isotropic

Anisotropic

Hydraulic Conductivity Values

Freeze and Cherry, 1979

Layered media (horizontal conductivity)

M

ii

M

ihii

h

b

KbK

1

1

Q1

Q2

Q3

Q4

Q = Q1 + Q2 + Q3 + Q4

K1

K2

b1

b2

Flow

Layered media(vertical conductivity)

M

ihii

M

ii

v

Kb

bK

1

1

/Controls flow

Q1

Q2

Q3

Q4

Q = Q1 = Q2 = Q3 = Q4

R1

R2

R3

R4

R = R1 + R2 + R3 + R4

K1

K2

b1

b2

Flow

The overall resistance is controlled by the largest resistance: The hydraulic resistance is b/K

Aquifers

• Lithologic unit or collection of units capable of yielding water to wells

• Confined aquifer bounded by confining beds

• Unconfined or water table aquifer bounded by water table

• Perched aquifers

Transmissivity

• T = Kb

gpd/ft, ft2/d, m2/d

Schematic

i = 1

i = 2

d1

b1

d2

b2 (or h2)

k1

T1

k2

T2 (or K2)

Pumped Aquifer Heads

i = 1

i = 2

d1

b1

d2

b2 (or h2)

k1

T1

k2

T2 (or K2)

Heads

i = 1

i = 2

d1

b1

d2

b2 (or h2)

k1

T1

k2

T2 (or K2)

h1

h2

h2 - h1

LeakanceLeakage coefficient, resistance (inverse)

• Leakance

• From below:

• From above:

d

k

1

11

i

iiiv d

khhq

1

11

i

iiiv d

khhq

Flows

i = 1

i = 2

d1

b1

d2

b2 (or h2)

k1

T1

k2

T2 (or K2)h1

h2 h2 - h1

qv

Poisson Equation

2

2

,TqR

xhhh

vxxxx

yx

T

qR

x

h v

2

2