# Stream Gradient and Sediment Erosion

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```					                          GK12 Module Teacher’s Guide

Rachel Couch

Abstract:
This activity will help students understand the relationship between stream
gradient and sediment erosion. A pipe representing a river is set on a stack of
books, which will represent various gradients. Students will time how long it takes
water to travel down the pipe at different gradients. This will allow students to
see how a steep gradient moves water faster than a shallower gradient, as well as
how a steep gradient causes more sediment erosion than a shallower gradient.

Objectives:
The students will understand that the gradient of a river causes water to
move at different speeds, and thus gradient affects erosion at different speeds.
The steeper the gradient the more erosion will occur.

National Standards:

Standard   A: Science as Inquiry; Abilities necessary to do scientific inquiry
Standard   A: Science as Inquiry; Understandings about scientific inquiry
Standard   B: Physical Science; Motions and forces
Standard   D: Earth and Space Science; Structure of the earth system

New Mexico Standards:

Strand 1, Standard 1: Scientific Thinking and Practice; Use scientific method
Strand 1, Standard 1: Scientific Thinking and Practice; Understand process of
scientific investigation
Strand 1, Standard 1: Scientific Thinking and Practice; Use mathematical ideas,
tools, techniques
Strand 2, Standard 1: Physical Science; Transfer, change, and conservation of
energy
Strand 2, Standard 3: Earth and Space Science; Earth and atmosphere structure

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GK12 Module Teacher’s Guide

Materials:
 8 to 10 foot long pvc pipe
 Several drinking straws
 1 large plastic container (sweater box)
 Numerous text books
 1 stop watch
 1 measuring tape
 1 calculator
 1 large drinking glass of water

Background:
The slope of a river is called its gradient. Generally rivers that have steep
gradients are immature rivers that occur in a mountain setting, and rivers that
have very shallow gradients are mature rivers in valleys.
The pipe setup with the lowest slope or gradient will make the water take
the longest time to reach the plastic bin, and the pipe setup with the highest slope
will have the shortest travel time. The steeper the gradient of a river the more
force the water will have on the rocks that it is moving over. Therefore, an
immature river with a steep gradient will erode more sediment than a mature river

Procedures:
Setup

   Stack up text books beneath one end of the pvc pipe and the plastic bin
underneath the other end of the pipe.
   Have one student measure the height of the pipe, from the ground to the
base of the pipe; record this measurement.

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GK12 Module Teacher’s Guide

   Have one student measure the length of the pipe (as shown on diagram) on
the floor; record this measurement.
   Have one student hold a drinking straw in water and then place their thumb
over the top of the straw to keep the water in.
   Have the same student lay the straw in the pipe making sure they keep the
straw parallel to the pipe. This is to ensure that the water is not
accelerated by faster pouring rates or a straw that is at a steeper slope.
   Have one student waiting at the end with the plastic bin with a stop watch.
   Have one student in charge of starting the experiment; they must make sure
that the students on both ends of the pipe are prepared. When this student
says go, the student with the stopwatch will start the watch, and the
student with the straw will let the water go.
   The student with the stopwatch will stop the watch when the first drop of
water hits the plastic bin; record this measurement.
   Repeat this process 5 times without changing the height of the textbooks.
   Add more textbooks beneath the high end of the pipe, and repeat the entire
process.

Predictions
We will be measuring the speed of water down a tube with the top of the tube at
three different heights, giving us 3 different gradients. Predict which will have
the slowest speed, which will have the fastest and which will be in the middle.

3
GK12 Module Teacher’s Guide

Measurements

Run 1
Height             MEASURE in Inches
Conversion to cm Line 1 * 2.54
Length             MEASURE in Inches
Conversion to cm Line 3 * 2.54
Water time      MEASURE
(sec)           In seconds
Water speed     Line 6/       Line 6/    Line 6/    Line 6/   Line 6/
(cm/sec)        Length        Length     Length     Length    Length
Average         Line 7 Sum/5
Speed

Run 2
Height             MEASURE in Inches
Conversion to cm Line 1 * 2.54
Length             MEASURE in Inches
Conversion to cm Line 3 * 2.54
Water time      MEASURE
(sec)           In seconds
Water speed     Line 6/       Line 6/    Line 6/    Line 6/   Line 6/
(cm/sec)        Length        Length     Length     Length    Length
Average         Line 7 Sum/5
Speed

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GK12 Module Teacher’s Guide

Run 3
Height             MEASURE in Inches
Conversion to cm Line 1 * 2.54
Length             MEASURE in Inches
Conversion to cm Line 3 * 2.54
Water time      MEASURE
(sec)           In seconds
Water speed     Line 6/       Line 6/    Line 6/    Line 6/   Line 6/
(cm/sec)        Length        Length     Length     Length    Length
Average         Line 7 Sum/5
Speed

Results
Write your conclusion for this experiment below (What happened and Why?)
___The setup with the lowest gradient made the water speed the slowest, and
the setup with the highest gradient made the water speed the highest because
the water had more potential energy.
___________________________________________

Were the results of the experiment consistent with your predictions?
____Yes/ No _____________________________________
______________________________________________________

Relationship to Erosion
Which gradient gave the water the most energy?
_____________The steepest ______________________________

What does this mean about the amount of force that the water exerted on the
plastic box when it arrived?
__The steepest gradient gave the water the most force ___________
_________________________________________________________

Which of our gradients could pick up the largest rock particle?
__The steepest one ________________________________________

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GK12 Module Teacher’s Guide

What setting in nature could carry the largest rock particles, a mountain stream, a
gently sloping stream, or a valley stream with a low gradient.
___A Mountain stream ______________________________________

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GK12 Module Glossary

Gradient – slope of a river

Immature river – a river with a steep gradient found in mountain settings

Kinetic energy – the energy of motion

Mature river – a river with a shallow gradient found in valleys

Potential energy – stored energy

1
GK12 Module Student’s Guide

Predictions
We will be measuring the speed of water down a tube with the top of the tube at
three different heights, giving us 3 different gradients. Predict which will have
the slowest speed, which will have the fastest and which will be in the middle.

Measurements
Run 1
Height
Conversion to cm
Length
Conversion to cm
Water time
(sec)
Water speed
(cm/sec)
Average Speed

2
GK12 Module Student’s Guide

Run 2
Height
Conversion to cm
Length
Conversion to cm
Water time
(sec)
Water speed
(cm/sec)
Average Speed

Run 3
Height
Conversion to cm
Length
Conversion to cm
Water time
(sec)
Water speed
(cm/sec)
Average Speed

3
GK12 Module Student’s Guide

Results
Write your conclusion for this experiment below (What happened and Why?)
______________________________________________________________
____________________________________________________

Were the results of the experiment consistent with your predictions?
______________________________________________________________
____________________________________________________

Relationship to Erosion
Which gradient gave the water the most energy?
_________________________________________________________

What does this mean about the amount of force that the water exerted on the
plastic box when it arrived?
______________________________________________________________
____________________________________________________

Which of our gradients could pick up the largest rock particle?
______________________________________________________________
____________________________________________________

What setting in nature could carry the largest rock particles, a mountain stream, a
gently sloping stream, or a valley stream with a low gradient.
_________________________________________________________

4

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