Lecture 12

Lecture 12

Homogeneity and Isotropy

Fetter 4.11

Homogeneity and Isotropy

The thickness of an aquifer is important.

response (hydrogeologic) of an aquifer is function (aquifer properties and thickness)

Homogeneous - a geologic unit that has the same properties at all locations.

K, n, b, vary little

T,S are constant throughout unit.

Heterogeneous - Hydraulic properties vary spatially.

Thickness, K, n

Examples (A, B, C) of heterogeneous aquifers.

Isotropic - The condition in which hydraulic properties of the aquifer are equal

in all directions.

Varies with grain shape and orientation

Anisotropy - The condition under which one or more of the hydraulic

properties of an aquifer vary according to the direction of flow.

	Intrinsic permeability may vary with direction fractured rocks!



	K_n - Horizontal hydraulic conductivity

	K_v - Vertical

Chapter 5- Principles of Ground-water flow

Ground water possesses-

Mechanical Thermal and Chemical forms of energy.

Ground-water flow controlled by Physics and thermodynamics Usually ignore (low T)

Three forces act on ground water

	1) Gravity

	2) External pressure - atmospheric, overlying water

	3) Molecular attraction - surface tension

The total energy of a unit volume of water is sum of all three components.

Kinetic - energy due to motion of water

Gravitational - potential energy due to the position of a fluid mass wrt datum.

z = elevation of center of gravity of fluid above reference elevation.

Fluid pressure à energy due to surrounding fluid pressure.

Divide by r


	- basic equation of fluid mechanics

	= constant for a frictionless, incompressible fluid.

Divide by g

	-place units in Energy or J or m(l)
Place units in or or m(L)

Because ground water velocity is generally small, Kinetic energy term is neglected.

= pressure head (height of water column providing head)

= z +

Total Head = sum of elevation head and pressure head, dimensions (L)

ENV 302 - Lectures