Flow in AquifersGroundwater Hydraulics

Daene C. McKinney

Summary

• Confined Aquifer Flow– Continuity Equation– Steady Horizontal Flow– Transmissivity

• Unconfined Aquifer Flow– Continuity Equation– Steady Horizontal Flow– Steady Horizontal Flow with Infiltration– Drains

Unconfined Aquifer Flow

Flow in an Unconfined Aquifer• Dupuit approximations

– Slope of the water table is small– Velocities are horizontal

Ground surface

Bedrock

Unconfined aquifer

Water table

Dx

Qx

K

h

x

yz

Steady Flow in an Unconfined Aquifer

• 1-D flow

• Steady State

• K = constant

h

FlowhA

hB

Water Table

Ground Surface

Bedrock Lx

Steady Flow in an Unconfined Aquifer With Infiltration

hhMax

FlowhA

hB

Water Table

Ground Surface

Bedrock

N, Infiltration

Lx

Steady Flow Constant K

Steady Flow in an Unconfined Aquifer With Infiltration

hhMax

FlowhA

hB

Water Table

Ground Surface

Bedrock

N, Infiltration

Lx

hhMax

FlowhA

hB

Water TableGround Surface

Bedrock

N, Infiltration

Lx

Steady flow in an unconfined aquifer with infiltration

Example (Embankment)

• GivenL = 3000 mK = 20 m/dayhA = 30 m

hB = 20 m

N = 500 mm/yr

• Find: Flow to the streams and shape of water table

hhMax

FlowhA

hB

Water Table

Ground Surface

Bedrock

N, Infiltration

Lx

Example (Cont.)

hhMax

FlowhA

hB

Water Table

Ground Surface

Bedrock

N, Infiltration

Lx

Example (Drains)• Subsurface drains are often used to prevent the water table elevation from

increasing to an elevation where it would waterlog the roots of crops or bring unwanted salts and other chemicals in to the root zone.

• Steady, 1-D flow , homogeneous, isotropic aquifer, w/infiltration

hd

hMax

Water Table

Ground Surface

Lower Confining Layer

N, Infiltration

Lx

Summary

• Confined Aquifer Flow– Continuity Equation– Steady Horizontal Flow– Transmissivity

• Unconfined Aquifer Flow– Continuity Equation– Steady Horizontal Flow– Steady Horizontal Flow with Infiltration– Drains