1
Name: __________________________________ Period: ___________ Date: ___________
Lab
3

4
: Deposition of Sediments
80 Minutes
Swiftly flowing streams can carry large amounts of sediment as they move downhill. When such streams
flow into calm bodies
of water (lakes, or sheltered lagoons and bays) they lose their ability to support the
sediments. Particles of sediment settle to the bottom of the still water at varying rates. Knowing how
sediments are deposited helps you understand how sedimentary roc
ks are formed.
Objective:
You will determine the factors that control the rate of sediment deposition in quiet water.
Procedure A:
THE EFFECT OF PARTICLE SIZE ON SEDIMENTATION
1. Set up a plastic column on a ring stand using tube clamps.
2
Be sure that
the bottom cap is on tightly. Fill the tube ¾ full of water.
3.
Draw two horizontal lines on the outside of the tube. One line should be 6 cm below the surface of
the water near the top of the tube and the other line should be 4 cm above the bottom of the tu
be.
4.
Obtain from your instructor a variety of sediment sizes of the same material.
5.
Beginning with the largest size sediment, measure the average diameter in millimeters. Determine the
settling time by dropping a pinch of the sediment into the tube. Start t
he stopwatch when the
particles first reach the top horizontal line and stop it when the first particles reach the second line
near the bottom of the tube. Record the average diameter of the sediment and the settling time to the
nearest hundredth on your
Report Sheet, then round your reading to the nearest tenth of a second.
Then complete the chart as indicated.
6.
Repeat Procedure 5 for all of the different sediment sizes.
7.
Measure the distance, in centimeters, between the two lines drawn on the outside of t
he column.
Record this distance on your Report Sheet.
8.
On Graph A, plot a point for the settling time of each sediment size. Use the scale on the left side of
the grid. Connect the points with a smooth line using a red pencil.
9.
Using the settling times me
asured in procedures 5 and 6 and the distance between the two lines in
measured Procedure 7, calculate the settling rate for each particle size. Refer to the equation for rate
of change found in the Appendix. Record your results on your Report Sheet.
10.
On
Graph A, plot a point for the settling rate of each sediment size. Use the scale on the right side of
the grid. Connect the
points with
a smooth line using a blue pencil.
Procedure B:
THE EFFECT OF PARTICLE DENSITY ON SEDIMENTATION
1.
Obtain from your i
nstructor samples that are the same size and shape but of different densities
(highest, high, medium, low,
and lowest
).
2.
Beginning with the highest density sediment, determine the settling time by dropping the particle into
the tube. Record the density an
d the settling time to the nearest hundredth on your Report Sheet, then
round your reading to the nearest tenth of a second. Then complete the chart as indicated.
3.
Repeat Procedure 2 for all of the different density sediments.
4.
On Graph B, plot a point for
the settling time of each density particle. Use the scale on the left side
of the grid. Connect the points with a smooth line using a red pencil.
5.
Using the settling times measured in Procedures 2 and 3 and the distance between the two lines
measured in P
rocedure A, calculate the settling rate for each density particle. Refer to the equation
for rate of change found in the Appendix. Record your results on your Report Sheet.
6.
On Graph B, plot a point for the settling rate of each density particle. Use the
scale on the right side
of the grid. Connect the points with a smooth line using a blue pencil.
2
Procedure C:
THE EFFECT OF PARTICLE SHAPE ON SEDIMENTATION
1.
Obtain from your instructor, samples which are the same volume and density but diffe
r in
roundnes
s.
2.
Beginning with the most spherical, determine the settling time for each of the particles.
3.
Record the shape and settling time to the nearest hundredth on your Report Sheet, then round your
reading
to
the nearest tenth of a second. T
hen complete the chart as indicated.
4.
On Graph C, plot a point for the settling time of each particle shape. Use the scale on the
left side of
the
grid.
5.
Connect the points with a smooth line using a red pencil.
6.
Using the settling times measured in Proced
ure 2 and the distance between the two lines
measured in
Procedure A, calculate the settling rate for each density particle. Refer to the equation for rate of change
found in the Appendix. Record your results on your Report Sheet.
7.
On Graph B, plot a poin
t for the settling rate of each density particle. Use the scale on the right side of
the grid. Connect the points with a smooth line using a blue pencil.
Procedure D:
SEDIMENTATION OF MIXED PARTICLES
1.
Observe the pattern of vertical deposition of the
m
ixed sediments.
2.
On the diagram of a plastic tube, draw what you
observed.
3
Procedure A
Distance Traveled: __________cm
Grain
Size
Settling
Time
(actual)
Settling
Time
(nearest
tenth)
Settling
Rate
(nearest
tenth)
Procedure B
Distance Traveled: __________cm
Grain
Density
Settling
Time
(actual)
Settling
Time
(nearest
tenth)
Settling
Rate
(nearest
tenth)
Procedure C
Distance Traveled: __________cm
Grain
shape
Settling
T
ime
(actual)
Settling
Time
(nearest
tenth)
Settling
Rate
(nearest
tenth)
GRAPH A
Grain Size (mm)
GRAPH B
Density (g/cm³)
GRAPH C
Spherical

Flat
Shape
4
Questions:
(Answer in Complete Sentences)
1.
How does each of the following affect the rate at which particles settle in quiet water when
other factors are equal?
a)
Size:
b) Density:
c) Shape:
2.
What size particles seem to stay suspended indefinitely in a quiet b
ody of water?
3.
What is your description of the appearance of material which accumulates on the bottom of
the tube (procedure D) following the addition of a mixed sample of sediments to quiet water?
4.
The profile below shows the average diameter of sedim
ent that was sorted and deposited in
specific areas.
A, B, C,
and
D
by a stream entering an ocean.
Describe the process by which
this sorting occurs.
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