Go With the Flow
Objective:
Students will be able to measure stream velocity and calculate
volume of water in the stream channel to determine flow, also
known as discharge.
Location:
Outdoors
Time Required:
65 minutes
Subjects:
Science, Math
Alignment to NC Essential Standards for Science:
8.E.1
Een.2.3.
EEn.2.4
Background:
Stream flow, or discharge, is the volume of water that moves over a designated point
over a fixed period of time. It is often expressed as cubic feet per second (cfs). The flow
of a stream is directly related to the amount of water moving off the watershed into the
stream channel. It is affected by weather, increasing during rainstorms and decreasing
during dry periods. It also changes during the different seasons of the year, decreasing
during the summer months when evaporation rates are high and shoreline vegetation is
actively growing and removing water from the ground. August and September are
usually the months of lowest flow for most streams and rivers in the country.
Flow also has a large impact on water quality and the living organisms and habitats
within the stream. Large, swiftly flowing rivers can receive pollution discharges and be
only slightly affected, whereas small streams have less capacity to dilute and degrade
wastes. Stream speed, 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 fastflowing areas, others need quiet pools). Stream flow also affects the amount of silt and
sediment carried by the stream. Sediment introduced to quiet, slow-flowing streams
will settle quickly to the stream bottom. Fast moving streams will keep sediment
suspended longer in the water column. Lastly, fast-moving streams generally have
higher levels of dissolved oxygen than slow streams because they are better aerated.
Materials: Each group will need:
 Yardstick for measuring water depth
 Orange or another floating object
 Stop watch or watch with second hand
 Pencil and clipboard
 Plastic Tape Measure
 Two flags to mark the stream
 Copies of the Calculating the Flow Worksheet
Note: It is vital to know the potential upstream contaminants reaching the stream.
Animal waste, agricultural runoff (pesticides, herbicides, etc.), industrial wastes, or
sewage leaks can be hazards to students and you. If you find a stream with any of the
above contaminants, a class must use proper precautions if you decide to collect
samples in the stream. Students should wear protective boots, gloves, and goggles when
necessary. In case of serious contamination, notify local authorities.
Note: Do not choose a deep pool or riffle. Flowing water is dangerous and students should not
be in the water above their knees. If it is moving too fast, do not let the students get in the water.
On the other extreme, make sure you have at least a minimal flow of 2 inches, otherwise it will be
too shallow to conduct this activity.
Procedures:
1. Prior to starting the field portion, lead a discussion on stream flow and its influences.
2. Next head out to the stream site. Divide students into teams of four (4). Each team
should pick a 20-foot section of the stream to work in. Ideally each team should have
their own space, but if
that is not possible due
to accessibility have
two teams share the
same 20 foot section,
but run the test
separately. Hand out
one set of materials to
each team and a copy
of the Calculating
Stream Flow
Worksheet to each
person.
AREA
3. Each team will now calculate the area of a stream cross section in square feet. (Area =
depth x width) Measure the depth of the stream by starting at the water’s edge and
moving across the stream taking several measurements along the way. Then take the
average of the depth measurements. Record results on the calculating stream flow
worksheet.
4. Next run the tape measure across the stream (from water’s edge to water’s edge).
Measure the width of the stream at two locations. Take the average of the two
measurements. Record results on the calculating stream flow worksheet.
5. Multiply the average width and average depth of your stream to determine its area in
square feet. Record results on the calculating stream flow worksheet.
SPEED
6. Next, each team will calculate the speed of a stream by measuring the rate at which it
flows in feet per second (ft/sec).
7. Starting from the point where the stream area measurements were taken, mark off a 20foot section downstream using flags or have two students hold each end of the
measuring tape.
8. Each team member picks one of the following jobs: starter, timer, catcher, and recorder.
The starter stands at the upstream flag and the catcher stands at the downstream flag
with the timer and recorder.
9. Using a stopwatch, the timer will measure how many seconds it takes an orange to float
a 20-foot distance. An orange is a good object to use because it has enough buoyancy to
float just below the water surface. It is at this position that maximum velocity typically
occurs.
10. The starter should position the orange so that it flows into the fastest current. The
catcher catches the orange as it passes the downstream flag. The recorder should record
the time measured.
11. This "time of travel" measurement should be conducted at least three times and the
results averaged – the more trials you do, the more accurate your results will be.
12. Discard any float trials in which the object gets hung up in the stream (by cobbles, roots,
debris, etc.).
13. After obtaining the average time, divide the distance in feet by the number of seconds it
took the orange to travel that distance. Record results on the “Calculating Stream Flow”
worksheet. This is the speed in feet per second.
FLOW
14. Scientists have determined that a coefficient or correction factor is needed for
streams due to fact that water at the surface travels faster than near the stream
bottom due to resistance from gravel, cobble, etc. By multiplying the surface
velocity by a correction coefficient, it decreases the value and gives a better
measure of the stream's overall velocity. The coefficient or correction factor is 0.8
for rocky-bottom streams or 0.9 for muddy-bottom streams.
COEFFICIENT = 0.8 for rocky-bottom streams
COEFFICIENT = 0.9 for muddy-bottom streams
15. To determine flow rate, multiply your stream area by your stream speed. Then
multiply that answer by the coefficient, depending on whether you have a rocky
or muddy bottom stream.
FLOW = AREA X SPEED X COEFFICIENT
Here is another way to express flow: FLOW = ALC/ T
A = Average cross-sectional area of the stream in feet (average stream width
multiplied by average water depth).
L = Length of the stream reach measured (usually 20 ft.)
C = Coefficient (0.8 for rocky-bottom streams or 0.9 for muddy-bottom streams).
T = Time, in seconds, for the float to travel the length of L.
16. Enter your results on the “Calculating Stream Flow” worksheet
17. Once all the groups have completed their measurements, compare the results.
Were all the results the same or different? If different, what might have caused
them to be different? (possible answers: slope, width of stream, objects in the
channel, deep verses shallow water, gravel substrate verses sandy substrate)
Evaluate:
For grades 8 - 9:
1. Calculate the velocity of the stream if the orange floats at a rate of 100 feet in 1.5
minutes.
2. Calculate the flow rate of a muddy bottom stream if the average width is 5.5 ft and
average depth is 17 inches and the orange floats at a rate of 67 ft in 2.4 minutes.
3. What does the flow tell you about the watershed?
4. What unit is flow measured in?
5. When velocity increases in a stream, what happens?
6. What factors contribute to an increase in water flow?
For grades 9 - 12:
1. If the average depth of the stream is 4 ft and width is 7.5 ft and it took the orange
10 seconds to travel the 10-foot length of the stream, what is the volume?
2. If two streams drain equal sized and comparable watersheds, and one watershed
is forested while the other is urban, which will have a greater discharge of water?
Why?
Extension:
1. In the last step, the students compared their results and hypothesized what caused
them to be different. As an extension, have the students investigate streams in their
community noting changes that might have been made to them and how it has
affected stream flow. Also have the students look at what are some of the
consequences that occur as a result of those changes to the stream.
2. Have students convert the various measurements to metric.
Adapted from Georgia Adopt-A-Stream Educator’s Guide
Based on Georgia Adopt-A-Stream Visual Stream Survey procedures.
CALCULATING STREAM FLOW
Flow = Area X Speed X Coefficient
CALCULATE AREA
Area = depth x width
It is advisable to take multiple depth and width measurements
always start at the waters edge with a first measurement of zero
all data should be recorded in feet, with inches replaced by increments of 10
depth measurements
1.
0 ft
2.
average
depth
3.
4.
1.
2.
average
width
width
=
7.
8.
sum
sum
sum of width measurements
number of measurements
=
Area
6.
sum of depth measurements
number of measurements
=
width measurements
5.
X
depth
CALCULATE SPEED-measure the time it takes a float to travel a desired distance
It is advisable to take at least 2 measurements of current speed
take measurements from the stream run
length in
time in seconds
1.
2.
average time
3.
4.
20 feet is
recommended
sum
sum of time measurements
number of measurements
=
length in feet
average time in seconds
=
Speed
feet
CALCULATE STREAM FLOW
Flow
cfs
=
Flow in cubic feet per second
Area
X
Speed
X
.9 coefficient for muddy bottom stream
.8 coefficient for rocky bottom stream
Coefficient
Measuring Channel Cross-Section
Objective:
Students will document changes in stream-channel shape, or
stream profile, by measuring the stream channel crosssection.
Location:
Outdoors at local stream
Time Needed:
60-90 minutes
Subjects:
Science, Math
Alignment to NC Essential Standards for Science:
8.E.1
Een.2.3.
EEn.2.4
Background:
Water is a naturally eroding agent of soil. Over time, streams and rivers carve
out their unique path and shape. However, human activities have altered the
shape and path of many waterways by straightening them out or reducing their
floodplain areas. By measuring the cross section of a waterway, scientists have
been able to monitor changes in stream shape, also called profile.
Materials:








100-foot engineering measuring tape (has feet marked off in tenths)
8- to 10-foot measuring stick in increments of feet and tenths (you
can construct one from materials available at the hardware store)
Thick twine (preferably non-stretch builders’ quality)
Line level
2- to 3-foot lengths of rebar, nails and hammer (for first measurement)
Clips or vise grips to fix tape to rebar or nails.
Stream Channel Cross-section Measurement Data form and graph paper
Pencil
Note: Why feet in tenths? Engineering tape measures have feet graduated in tenths
instead of inches. When stream cross-sections are “professionally” conducted,
engineering tape is used. If you wish to use inches or metrics, that is fine, just remember
to use the same measuring units each time!
Procedure:
1. Locate a representative section of your stream. Make sure there are no
stream hazards—think safety first! Ideally, your site will have some kind
of permanent marker that will help you identify it in the future, e.g. a
large tree, concrete structure, etc. If a permanent marker is not available,
use rebar to mark the endpoints on each bank. The end points should be
set back from your stream, behind the bankfull stage on either side.
End points should be set back from the bank so that if erosion occurs, you will be able to capture that measurement the next time.
2. Stretch your twine between your
permanent markers. Using the line level,
make sure the twine is perfectly level. If
the twine is not level, your vertical
measurements (elevation) will not be
accurate. Stretch the measuring tape
between both endpoints directly beside
your twine. Attach the zero end of the
tape to the left permanent marker (when
looking downstream). Stretch the tape
tight and level above the water. You will
Eying line level to ensure accurate measurements
be taking vertical measurements from the
stream substrate to the twine and horizontal
measurements along the measuring tape.
3. Starting with the left endpoint at zero, measure horizontal distance along
the measuring tape every 2 feet and at each significant stream feature.
This includes drops in the streambed or sides, bankfull stage, edge of
water, deepest point, sandbars, etc. At those horizontal distances,
measure the vertical distance (or elevation) from bank or stream bottom to
twine. All measurements are taken from the left bank, when facing
downstream. All data should be recorded in feet, with inches replaced by
increments of 10. Continue across the channel to the right endpoint.
Under Comments, note when you are at the bankfull stage, edge of water
and other significant features.
4. Record the distance and elevation measurements.
5. On a sheet of graph paper, graph your stream profile to compare future
and past measurements. Be sure to include left and right bankfull, water’s
edge and sand bars.
Stream profile depth measurements every 2 feet and at each important stream feature
Evaluate:
1. Ask the students to discuss what causes erosion of the banks. What
causes deposition of sediment?
2. Do the students expect to see changes in the shape of the stream over
time? Why?
3. Ask the students to calculate discharge using the measurements obtained
in the cross-section.
4. Why does the y axis start with zero at the top?
Adapted from Georgia Adopt-A-Stream Educator’s Guide
Based on Georgia Adopt-A-Stream Visual Stream Survey procedures.
Stream Channel Cross-section Measurement Data
Group:
Date:
Location:
CROSS-SECTION
Distance from
Measurement
LEFT Pin
Depth
Point Ft.
Ft.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Comments
CROSS-SECTION
Distance from
Measurement
LEFT Pin
Depth
Point Ft.
Ft.
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
Comments
Measurements are always taken from the left stream bank, looking down stream.
Depth measurements are taken every 2 feet and in sections where there is a notable
change. Be sure to note left and right bankfull, water’s edge, and sand bars.
Here is an example of how to graph your stream profile. The resulting graph is a
bank-to-bank view of the features of the cross section. All measurements are in
feet.
How Much Water Falls Here?
Objective:
Students will calculate the volume of water that falls onto an
area of the school parking lot.
Location:
Indoors/Outdoors
Time Needed:
90 minutes (can be divided into two class sessions)
Subjects:
Science, Math
Alignment to NC Essential Standards for Science:
8.E.1
Een.2.3.
EEn.2.4
Background:
When it rains, where does the water go? Some of it is absorbed by the soil and plants,
some is evaporated back into the air and some runs off the land. When it rains in areas
with lots of impervious surface (parking lots, roofs, roads), water runs off to storm
drains and drainage ditches, often at a fast rate because it is not absorbed into the
ground.
Urbanization and other development often adversely affect stream health by increasing
the volume of surface runoff entering a local waterway. Urban stormwater runoff may
contain sediment, debris, oil, gasoline, and heavy metals (nonpoint source pollution)
that it has picked up after traveling over impervious surfaces. When potential
pollutants are transported quickly from the land to a waterway, this can cause a
phenomenon called “shock loading.” Shock loading is the overloading of water with
nutrients, sediment, oil, etc, over a very short period of time giving the organisms little
time to adapt to the changes in their environment. Shock loading can result in fish kills
or algal blooms depending upon the type of pollutants in the runoff. For example,
suspended materials in the runoff can also absorb and store heat that increases the
water temperature.
Materials:
 Yardstick

Trundel wheel (optional)
 Writing materials

Local rainfall data
 Tape measure

Clipboards (optional)
 Graph paper

Calculators
 Rulers
 Long piece of twine (meter and foot intervals)
Preparation:
Check online to find out the average annual rainfall for your area.
Procedures: Explain to the students they are going to calculate the volume of runoff
from the school parking lot that flows to the nearest stream.
1. Divide the class into teams of 3-5 students.
2. Draw a sketch of the parking lot on the board. Have each team select an area
they wish to measure. If the lot has multiple sections, give each group a
certain area to measure. Note: Make sure the students use the same measurements
(feet or meters).
3. Have the students go outside and take needed measurements. Transfer
all measurements to the sketch on the board.
4. Have students copy a sketch of the parking lot with all measurements
on a regular piece of paper (Grades 6th - 8th) and/or to scale on graph
paper (Grades 9th - 12th).
5. Have each team determine the direction the water runs off the parking
lot and locate the nearest stream. Note: A map can be used to find the
stream, if the stream is not next to the parking lot. Remember, if the
stormwater flows into a storm drain, the drain pipe will lead to the closest
stream or drainage ditch.
6. Have the students estimate the area of the parking lot. For example:
Square:
Area = Length X Width
Triangle:
Area = ½ Base X Height
The values should be in the units the students measured on the parking lot.
Add together all the individual shapes’ areas to find the total area of the
parking lot.
7. Determine the volume of rain falling on the parking lot annually by
multiply the average annual rainfall (convert to feet or meters) by the
overall area of the parking lot (square feet or meters). Volume should
be recorded in cubic feet (ft3) or cubic meters (m3).
Discussion:
1. Where does the runoff from the parking lot go?
2. What route does the runoff take? (Storm drain, drainage ditch, stream, culvert) Is
the area from the parking lot to the nearest stream vegetated or paved? If both,
estimate percentage of each.
3. Brainstorm ways to slow the flow of water coming from the school’s parking lot
to the stream (rain gardens, rain barrels, increase permeable surfaces).
Evaluate:
The following conversions are useful:
______________________________________
1 ft3 = 7.2827 gallons
1 m3 = 1,000 liters
5 minute shower = 25 gallons or 95 liters
Density of water = 1 gallon = 8.34 lbs.
1 liter = 1 kg.
_____________________________________
1. Have students calculate the following:
Average annual rainfall:
______________ inches
Convert rainfall from inches to feet
______________ ft (X 1ft/12in.)
Surface Area of Parking Lot
______________ ft2
Volume of runoff
______________ ft3
Convert volume of runoff to gallons
______________ gallons of runoff
Determine how many 5 min. showers
can be taken with the amount of
runoff
______________ showers
If you took a shower every day, how
long would it take to shower this
many times?
______________ years
Determine the weight of runoff in lbs.
______________ lbs.
2. Compare the estimates with each other to see the variations in values.
Adapted from Georgia Adopt-A-Stream Educator’s Guide
Based on the Environmental Resource Guide.