Streamflow lesson plan
TITLE
Measuring Streamflow with Stream Channel Geometry and the Twig Test
AUTHOR
Kirstin Neff
TOTAL TIME
15-20 minutes
GOALS
Students will calculate the streamflow (volume of water/time) of a stream to facilitate discussion of the sources of stream water and the factors contributing to the amount of water in the stream.
LEARNING OBJECTIVES
Students will be able to:
• Estimate the cross-sectional area of a stream using simple depth and width measurements.
• Measure the speed of water in a stream using a twig, stopwatch, and tape measure.
• Calculate the streamflow (volume of flow/time) from the estimated cross-sectional area and water speed.
• Identify the different potential sources of stream water.
NEXT GENERATION SCIENCE STANDARDS
5-ESS2-1.
Develop a model using an example to describe ways the geosphere, biosphere, hydrosphere, and/or atmosphere interact. [Clarification Statement: Examples could include the influence of the ocean on ecosystems, landform shape, and climate; the influence of the atmosphere on landforms and ecosystems through weather and climate; and the influence of mountain ranges on winds and clouds in the atmosphere. The geosphere, hydrosphere, atmosphere, and biosphere are each a system.]
MS-ESS2-2.
Construct an explanation based on evidence for how geoscience processes have changed Earth's surface at varying time and spatial scales. [Clarification Statement: Emphasis is on how processes change Earth’s surface at time and spatial scales that can be large (such as slow plate motions or the uplift of large mountain ranges) or small (such as rapid landslides or microscopic geochemical reactions), and how many geoscience processes (such as earthquakes, volcanoes, and meteor impacts) usually behave gradually but are punctuated by catastrophic events. Examples of geoscience processes include surface weathering and deposition by the movements of water, ice, and wind. Emphasis is on geoscience processes that shape local geographic features, where appropriate.]
HS-ESS2-5.
Plan and conduct an investigation of the properties of water and its effects on Earth materials and surface processes. [Clarification Statement: Emphasis is on mechanical and chemical investigations with water and a variety of solid materials to provide the evidence for connections between the hydrologic cycle and system interactions commonly known as the rock cycle. Examples of mechanical investigations include stream transportation and deposition using a stream table, erosion using variations in soil moisture content, or frost wedging by the expansion of water as it freezes. Examples of chemical investigations include chemical weathering and recrystallization (by testing the solubility of different materials) or melt generation (by examining how water lowers the melting temperature of most solids).]
Crosscutting Concepts:
Scale, Proportion, and Quantity
• Standard units are used to measure and describe physical quantities such as weight and volume. (5-ESS2-2)
Science and Engineering Practices:
1. Asking questions (for science) and defining problems (for engineering)
• (3-5) specify qualitative relationships
• (6-8) specify relationships between variables, and clarifying arguments and models
• (9-12) formulating, refining, and evaluating empirically testable questions
2. Developing and using models
• (3-5) build and revise simple models and use models to represent events
• (6-8) develop, use, and revise models to describe, test, and predict more abstract phenomena and design systems
• (9-12) use, synthesize, and develop models to predict and show relationships among variables between systems and their components in the natural and designed worlds
3. Planning and carrying out investigations
• (6-8) use multiple variables and provide evidence to support explanations
• (9-12) include investigations that provide evidence for and test conceptual, mathematical, physical, and empirical models
4. Analyzing and interpreting data
• (3-5) introduces quantitative approaches to collecting data and conducting multiple trials of qualitative observations. When possible and feasible, digital tools should be used.
• (6-8) extend quantitative analysis to investigations, distinguishing between correlation and causation, and basic statistical techniques of data and error analysis.
• (9-12) introduce more detailed statistical analysis, the comparison of data sets for consistency, and the use of models to generate and analyze data.
5. Using mathematics and computational thinking
• (3-5) extend quantitative measurements to a variety of physical properties and using computation and mathematics to analyze data
• (6-8) identify patterns in large data sets and using mathematical concepts to support explanations and arguments.
• (9-12) use algebraic thinking and analysis, a range of linear and nonlinear functions including trigonometric functions, exponentials and logarithms, and computational tools for statistical analysis to analyze, represent, and model data. Simple computational simulations are created and used based on mathematical models of basic assumptions.
6. Constructing explanations (for science) and designing solutions (for engineering)
• (3-5) use evidence in constructing explanations that specify variables that describe and predict phenomena
• (6-8) construct explanations supported by multiple sources of evidence consistent with scientific ideas, principles, and theories
• (9-12) generate explanations that are supported by multiple and independent student-generated sources of evidence consistent with scientific ideas, principles, and theories
7. Engaging in argument from evidence
• (3-5) critique the scientific explanations proposed by peers by citing relevant evidence about the natural world
• (6-8) construct a convincing argument that supports or refutes claims for explanations about the natural world
• (9-12) use appropriate and sufficient evidence and scientific reasoning to defend and critique claims and explanations about the natural world. Arguments may also come from current scientific or historical episodes in science.
INSTRUCTIONAL PROCESS
Materials
• All students should have their field notebook and a writing implement, so that they can draw a sketch of the cross-sectional area measurements, and record their data from the twig test.
• Stopwatch
• Nearby twigs
• Ruler
• Tape measure
• 1-3 calculators, depending on the group size
Setup
• In the student’s journals, there should be a page with a schematic of a stream cross section (see image attached). Before beginning the exercise, this image will be used to teach students how we can estimate the cross sectional area of a stream. This image can also be used in the discussion of how we can measure “how much” water there is—students can use the image to work through the idea of water as a volume.
• A location along a stream that is at least 2 inches deep (at the deepest point) and at least 1 ft wide should be chosen. The “straightest” stretch of the stream should be used for the experiment (i.e. the section with the least turns, rocks, or eddies).
Introduction/Engagement
Essential Questions
How can scientists measure how much water there is in nature?
Student Misconceptions
Begin by asking students how they might try to measure water at home (ex. a measuring cup). Once the students have come up with a few ideas of how they have measured water in the past, ask them how those methods would work for measuring the amount of water in a lake or stream? What are the problems posed by measuring water in the natural environment? What are some ideas for how we could estimate how much water is in a lake or stream? What measurements would we need to take? If one of the students doesn’t mention it, be sure to highlight the problem of the water moving downhill in streams (whereas lakes are mostly stationary). Ask students what they think the word streamflow means? What does flow mean? Is flow a volume or a speed (or both)?
Some common misconceptions:
• To measure the amount of water in a stream, we should just measure the volume of the stream channel. (This doesn’t take into account the speed of the water—in the same amount of time, the stream could be holding a different volume of water depending on how fast it’s moving through the steam channel).
• It’s impossible to know how much water is in the stream, because we can’t measure the whole length of the stream at once.
• All that matters is the height of the stream: if it gets high, it’s flooding and has too much water to measure. (A stream could be at the same height, but have different speeds, and thus different streamflows).
Learning Structure
This exercise is for small groups. Each student in the group should take a turn either measuring the depth and width of the stream, measuring the length of the twig test, releasing the twig, or running the stop watch. If there are many students in the group, the twig test can be run one or two more times and an average of the three speeds can be used to calculate streamflow. This way every student can get a chance to participate in the measurement, or to do multiple different tasks. One student should always be in charge of writing the results of the test in the groups’ master data table in one of the student’s field notebook.
Exploration
Step-by-Step Description
Once you have developed the definition of streamflow with the students, and how to measure it, it’s time to actually measure your chosen stream. The steps for this exercise are as follows:
1. First, discuss with the students what measurements they will need to take, and have them draw a schematic of the stream cross section indicating what measurements need to be taken. An example schematic could be provided (attached). As they identify necessary measurements, have them create a data table in which to record their measurements (example data table attached). Ask them to make a guess (hypothesis/estimate) of how much water is in the stream in the sense of “How many gallons of water do you think are going by this spot in a second”?
2. Once the students have a schematic of the stream cross section and a comprehensive data table, ask the students what jobs need to be filled to take the measurements. One student each will be needed to: measure the width and various depths of the stream, measue the length of the twig test, release the twig, run the stop watch, yell “stop” when the twig crosses the finish line, and record the time in the data table.
3. First, a student will use a measuring tape to measure the width of the chosen stream cross section. Keeping the measuring tape stretched across the stream, another student will use a ruler to measure the depth of the stream 1/6th the distance across the stream, halfway across the stream, and 5/6th the distance across the stream. These values are entered into the data table and will be used later to calculate the approximate cross-sectional area of the stream.
4. Next, a student used the measuring tape to measure and mark off the length of the stream through which the twig will float and be timed (should be a fairly strait section, about 4-8 feet long). Be sure that they mark the “starting” and “finish” lines of the length, and record the length in the group data table.
5. Finally, students will test several small twigs they find in the area to see which floats the best. Once they have chosen a twig, on student will stand at the “starting” line and drop the twig into the center of the stream, yelling “start!” Another student will start the stopwatch when the first student yells “start!” A third student standing at the “finish” line will yell “stop!” when they see the twig cross the “finish” line, and the student with the stopwatch will stop the stopwatch at that time. The time it took the twig to float from start to end is recorded in the group data table.
6. Once the first set of data is collected, use the pre-printed equations in their field notebooks for the cross-sectional area, twig speed, and streamflow to calculate streamflow from the data collected. Ask students to use the provided equations to make their own calculation, either working in a group or pairs with calculators. As students have questions, ask another student to try to answer them, or answer them aloud to the group or individually, depending on your feeling for the group dynamic.
7. Once a student or group has come up with an answer, ask them to explain how they got that answer to the group. If they have made any mistakes, ask them why they did the calculation that way, to see if you can get them to see their own mistake. After your volunteer, go through the calculation aloud with your group to make sure everyone’s calculations are correct and everyone understands how to get the correct answer.
8. Once you have an answer in cubic feet per second (cfs), help the students to do a unit conversion on their hypotheses of gallons/sec (there are 7.48 gallons in a cubic foot), and compare their result to their hypothesis. Did they over or underestimate the amount of water in the stream?
9. Depending on time and the size of your group, you may want to repeat the experiment with students doing different jobs, and possibly along another stretch of the stream, to compare those results with your first results.
Application
Why does it matter?
• After the experiment, ask the students what scientists might be able to do with this information. Some examples: predict how much water will arrive at a dam downstream; how big a flood is; how much water we will have to drink in the future; how much water is available for plants and animals.
• Ask the students to guess the average streamflows of rivers, based on their result for their mountain stream:
o Colorado River: 22,500 cfs
o Mississippi River: 593,000 cfs
o Amazon River: 7,381,000 cfs
o Nile River: 99,941 cfs
o Ganges River: 441,433 cfs
o Rhine River: 70,629 cfs
o San Pedro River: 12 cfs (often zero/not flowing)
Extensions and/or follow-up activities
An extension question: Where is the water in this stream coming from? (Ex. snowmelt, rain (if it has rained recently), slow-moving groundwater (water in the ground moving downhill slowly through the soil—originally from snow or rain that seeped into the soil). To illustrate the idea of surface water-groundwater interaction, ask them if they think the stream bottom is impermeable (nothing can move through it). Further information on stream-groundwater interactions linked to below.
A follow-up activity that you could suggest, and possibly provide pages in their field notebooks to facilitate, is to have them measure the flow of water out of their kitchen faucet or bathroom showerhead. With the help of a supervisor, the student would:
1. Put a measuring cup or jug underneath the spout
2. Turn the water on full blast
3. Use a stop watch to measure the time the spout is on, turning the spout off before the measuring container is overfull
4. The student would then divide the volume of water by the time to get the flow rate of the spout. After converting volumes from cups/liters to cubic feet per second (cfs), the students could compare the flow from their spout to the streamflow, and relate their home water use to the amount of water in the mountain stream.
Assessment
How will you know if students "got" it?
• They come up with the correct streamflow rate and can show their work on the calculations
• They can explain why we took a specific measurement (ex. “Why did we need to know the length of the twig course?”)
• They can explain why water in a stream is measured as a flow rate rather than a volume
For those who don’t “get it:”
• Have them compare their calculations with a neighbors whose are correct, so that they can discuss the differences between their calculations
• Spend individual time with them asking them why they have plugged the data into the equations as they have (while advanced students are working on through the calculations). Once you have caught them up, give them a hint on the next step to try to bring them up to speed.
• Ask them why we took certain measurements, and show where they come into the calculations
RESOURCES
A more detailed description of this experiment from the EPA:
This is a primer on stream-groundwater interactions:
REFLECTION
The one time I have done a (simplified) streamflow exercise was with a high school small inquiry group. They picked up the steps very quickly, but needed lots of time (~30 min) inside, with a white board, to understand and successfully do the calculations. If doing this exercise with younger students, it might make sense to have them do the exercise as described, but do the calculations for them and not spend as much time making sure every student can get the calculation correct. That way the students still get to be involved and conduct the activity, without causing great frustration when it comes to the calculations.
