NAME: ________________________________________
LAB - Streamflow
Date: _______
Adapted from Exploration in Earth Science, The Physical Setting, United Publishing Company, Inc
Introduction: Running Water flows downhill due to the pull of gravity. The rate of channel abrasion
varies from stream to stream. It depends on factors such as velocity, volume, channel characteristics, and
supply of rock fragments.
The velocity of a stream depends on its volume and slope. The grain size and weight of the largest
rock particles that a stream can transport depends on the stream’s velocity and volume.
Objective: You will determine the relationship between stream velocity, volume, and slope and its ability
to transport sediments of given size.
Hypothesis: Make a prediction about how the volume of water and slope of a stream affect the stream’s
velocity.
Vocabulary:
Discharge -
Procedure A:
1. Place a trough on the lab table so that one end overhangs a buck in the sink. Using a clinometer to
measure the angle between the trough and table surface, Lift and support the other end of the
trough until you have a 5 degree angle.
2. From the source end of the trough, measure 25 cm and mark the edge of it (starting mark) with
tape. Make a second mark 100 cm from the first mark. This is the end mark.
3. Attach one end of a length of rubber tubing to the lab faucet. The other end should be inside the
trough at the first (starting) mark.
4. Turn on the water at low velocity. Time how long it takes bits of paper to travel the 100 cm
between tape marks. Enter this time on your Report Sheet.
5. Calculate the velocity using the equation below:
Velocity (cm/sec) = Distance Traveled (cm)
Travel Time (sec)
6.
At the starting mark, drop a small particle (silt) into the flowing water and time how long it takes
the silt to travel 100 cm. Take the average of 3 trials for greater accuracy. Record this time on the
Report Sheet.
7. Repeat procedure #6 using large particles (sand) and record your results on the Report Sheet.
8. Adjust your faucet for a higher velocity. Repeat procedures #4 through #7 using this higher
velocity while maintaining the 5 degree angle.
9. Repeat the entire exercise for a 10 degree and 20 degree angle for both low and high velocity
flows. Be sure to enter all data on your Report Sheet.
10. Graph the slope versus velocity (graph 1) and slope versus erosion time for just the low faucet
settings for sand, silt, and water. Plot the data for both faucet settings on the same set of axes
using a different color or symbol for each. Label each graphed line.
SLOPE VS. VELOCITY FOR LOW AND HIGH SETTINGS
SLOPE VS. TRAVEL TIME FOR SAND, SILT, AND WATER (LOW SETTING)
Discussion Questions:
1. How did you increase the volume of flow in this experiment?
2.
At a 5 degree slope, what happens to the velocity of the stream when you increase the volume of
flow?
3.
If the volume remains the same, as the slope of the stream increases, what happens to its velocity?
4.
At a given velocity, which takes longer to move 100 cm, silt or sand?
5.
As slope increases, what happens to the rate of stream erosion?
6.
As volume of flow increases, what happens to the rate of stream erosion?
7.
What is the apparent relationship between the volume and slope of a stream and the size sediment
transported by it?
8.
Explain why stream velocity may change from season to season.
Conclusion: Discuss the relationship between the slope and discharge of a stream to the stream’s velocity.
How did this compare to your hypothesis?
Reading Comprehension: Read the article below on Stream Flow and answer the questions that follow (in
complete sentences).
Stream Flow
http://www.roguebasinwatersheds.org/Files/Stream%20Flow3.pdf
What is stream flow?
Stream flow, or stream discharge, is the volume of water passing a fixed point over a unit of time and is
usually expressed in cubic feet per second (cfs). Stream flow reflects the amount of water moving off of the
watershed and into the channel and the amount being removed from the stream. Flow can be affected by a
number of factors and can vary rapidly as those factors change.
What makes stream flow change?
Stream flow is affected by both natural and human factors and can respond rapidly to changes in flow
parameters. Weather has a significant affect upon stream flow; flows increase shortly after rain storms and
decrease during dry periods. Snow accumulations and melting also have a large effect upon stream flow,
with high flows coinciding with periods of melting snow. Rainfall and snowmelt vary seasonally,
subsequently stream flow also varies. Evaporation and water use by plants also can significantly affect
stream flow. Vegetation has the largest impact on flow during summer months when temperatures are high
and streamside vegetation uses the most water. August and September are generally the months of lowest
flow for most streams and rivers. Flow is also be influenced by subsurface water flow which responds to
the same factors, but at a delayed or slower rate.
Water withdrawal for irrigation and municipal water needs, and diversion for hydropower generation are
human factors that can significantly affect stream flow. Urbanization also affects flow by changing the rate
of water infiltration and runoff during rainstorms.
How is stream flow measured?
Flow is usually measured at specific or fixed locations in the watershed. To measure stream flow, the
velocity of water passing the location must be measured as well as the width and depth of the stream.
Stream velocity, which increases as the volume of the water in the stream increases, determines the kinds of
organisms that can live in the stream (some need fast-flowing areas; others need quiet pools). Velocity also
affects the amount of silt and sediment carried by the stream.
1. Name three ways in which weather affects stream flow.
2. Why is stream flow slowest in August and September?
3. Describe using the information in the reading how stream flow is measured.