What is primary porosity?
What is secondary porosity?
Porosity between grains
Porosity caused by fractures
What is a Confining layer?
-layer having low or no peremeability
What is an aquiclude? - layer of low permeability that can store and
transmit groundwater slowly between aquifers (now more commonly referred
to as “leaky confining layer”)
What is an aquifuge?
What is an aquitard?
- absolutely impermeable and contains no water
- general term for layers of low permeability
What’s the difference between this and this
What’s under the boxes?
1
2
3
4
5
6
What’s this??
What’s under the boxes?
Review
What is freshwater head? - height of a column of freshwater in a well is just
sufficient to balance the pressure in the aquifer at
that point
What is point water head? - the actual water level in a well or piezometer
What is Reynold’s number? - defines whether flow is laminar or turbulent...if
turbulent we can’t use Darcy’s Law or just about
any of the models/assumptions discussed in this
course
What is specific discharge
- groundwater velocity calculated using Darcy’s
law
What is average linear velocity? - the actual velocity the water moves through
(seepage velocity)
the aquifer
What is effective porosity?
- porosity used to calculate above
Darcy’s Law
defines flow potential in a porous medium in a linear
direction between 2 points of known head and is the basis for all laminar
groundwater flow modeling and equations.
Darcy’s Law
in it’s simplest form does not take into account
boundary conditions of the flow field, anisotopy, heteorogeneity, leaky
confining layers or other complexities that complicate reality.
- these complexities need to be build into groundwater models that
approximate reality...
v2
P
h
 z
2g
g
What’s this?
-Groundwater flow equations (which are all based on Darcy’s Law and
Conservation of mass
problems in computer models,
) can be used to solve complex flow
-or we can use analogs such as flow nets, and electrical flow analogs to
define the subsurface flow field (discharge/recharge areas, flow paths,
potential distribution, etc.)
- flow nets break the aquifer down into manageable chunks (flow tubes)
where we can apply Darcy’s Law directly (in the modified form of the flow tube
equations)
- in a homogeneous, isotropic media, flow lines will be .
opposite
and
to grad h
parallel
.
What’s this??
K1 tan  1

K 2 tan  2
- in a heterogeneous media (i.e. 2 layers with different K values) flow lines
and equipotential
lines will get refracted at boundaries of units with
different K values. Flow follows grad h because grad h is being refracted as well
- can predict the amount of refraction knowing K and the angle of flow on one
side or another of the boundary
What’s this??
- in anisotropic media, flow is deflected at some angle away from grad h
dependant on the degree of anisotropy
tensor
- amount of deflection can be calculated using a
ellipse
- Simple mathematical models of groundwater flow such as the Dupuit
Equation have been developed, but they are approximations only that ignore
complexities of natural aquifers