Department
of Earth Science |
Northeastern
Illinois University
PRINCIPLES
OF HYDROGEOLOGY
ESCI
337
Spring,
2004
Daily Objectives #17 (March
16, 2004)
Dr. Sanders
By
the end of today's class, you should be able to do the
following:
OLD BUSINESS
v Using Darcy's Law, evaulate and
interpret results
from the Darcy tube experiment.
v Sketch
the pathways of the dyes as they moved through the sand tank flow model
in our last class, and on your drawing, identify the
following components of a flow net: flow lines, boundaries,
and water table (a water table is just a
particular type of boundary).
NEW BUSINESS
Concepts
v Describe what a datum
is.
v Describe and sketch a piezometer.
On the sketch, show how it can be used to measure total
hydraulic head, elevation head, and pressure
head.
v Describe the interconnection
between surface water (lakes, streams) and ground water as shown on a
flow net.
v
Explain
and list characteristics of each of the following components of flow
nets: flow lines, equipotential lines
(contour lines), and boundaries.
v Define the following types
of flow system boundaries, and fill in the blanks in the table:
Type of Boundary
|
Definition/Example
|
Relationship to
Flow Lines
|
Relationship to Equipotential Lines
|
| no-flow
(impermeable) boundary |
|
|
|
| constant
head boundary |
|
|
|
water
table
|
|
|
|
v In addition to
the rules
described by the table above, complete the following rules of drawing
flow nets:
n Equipotential
lines must be _________________________ to flow lines.
n The geometric shape formed by two
adjacent flow lines
and
two adjacent equipotential lines is roughly
_______________________
or _________________________.
n Changes in the spacing of
equipotential lines or flow lines,
or changes in the sizes of "squares",
should be ____________________________.
Practice I
z Draw a flow net in plan view
showing flow to a gaining stream through a homogeneous
unconfined aquifer.
z On graph paper, draw a
quantitatively accurate flow net in cross section view showing flow to
a gaining stream through a homogeneous unconfined
aquifer bounded on the bottom by a low-permeability layer. Label
each equipotential line with its value! (Have a group member
check your work.)
z On your cross section flow net,
draw at least a dozen piezometers and show water levels in each.
(Have a group member check your work.)
z On a separate piece of graph
paper, trace the following features of your cross section flow net:
ground surface, water level in the stream, piezometers, and water
levels in piezometers. Do not draw the flow lines,
equipotential lines, or water table! Be sure you have provided
enough piezometers and water levels so that another person can
reproduce your flow net based on the information you give them.
Check with me if you have any doubt.
z Using someone else's sketch of
water levels in piezometers (I will assign this part), draw a
quantitatively accurate flow net, including flow lines, equipotential
lines, and water table.
Practice II
u Draw a quantitatively accurate
flow net for flow beneath the dam on the handout provided. Be
sure to label equipotential lines with their value. For
simplicity's sake, let's all use the same datum: the flat bottom
of the main portion of the dam.
u Answer the following questions
about the dam flow net:
o If the sediments have a hydraulic
conductivity of 0.28 m/day, and the dam is 200 m long going back into
the page, calculate the flow rate of water under the dam. (Give
your answer in units of cubic meters/day.)
o At Point A, what is the total hydraulic
head? Elevation head? Pressure head?
Department
of Earth Science | Northeastern
Illinois
University
© 2004 Laura L.
Sanders.
Last updated March 16, 2004.