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Objective Teach students how to measure stream flow. Stream flow-- the amount of water moving through the stream per unit of time-- is a key parameter when assessing stream conditions. Stream flow or stream discharge is generally measured in units of cubic feet per second or m3/s. Higher than normal flows often appear turbid because of material picked up as the stream runs outside its banks. Lower than normal flows can stress riparian flora and fauna. Safety Precautions High water can make stream
gauging a potentially hazardous activity, depending on the size of the
stream that is being monitored. Scout out the stream before gauging to
make sure it is safe.
Activity Materials To contact the Water Resource Educator who can set you up with the materials, call (303) 413-7365 or send an email.
This activity can be conducted in a variety of ways. Stream gauging is a rather intuitive exercise. You measure the cross-section of the stream (m2) and then determine the time it takes for an object (i.e. stick or tennis ball) to move over a measured distance. Assuming the cross-section determined is relatively consistent over the measured distance: Cross-sectional area x speed of water = Stream discharge (m2) (m/s) (m3/s) Pick a section of the stream that has a fairly uniform flow and a uniform cross-section. Extend a tape measure across the cross-section and have two students hold each end. Another student should measure the depth of the stream at specific distances from one of the stream banks. Record all of the data so the cross-sectional area can be estimated back in the classroom, or as a homework assignment. AreaA + AreaB + AreaC + = Cross-sectional area of the stream After the cross-section data has been collected, it is now time to get the velocity of the water moving through your measured cross-section. Measure a distance above the cross-section (i.e. 3 meters). Make sure you pick a distance where the cross-section is relatively uniform. Measure the time it takes for a floating object (such as a stick or tennis ball) to move this distance (m/s). You now have sufficient data to estimate the stream discharge. The calculations are straightforward for those students with a basic understanding of geometry or the teacher can perform the calculations for younger students. It is often worthwhile to repeat the measurements several times and then take the average. Also measuring the stream discharge at different locations using the same method will help improve your confidence in your measured value. Flows plotted over time form a hydrograph which offer a visualization of a stream's seasonal flux.
NOTE: It may be worthwhile to "permanently" fix a yard stick or marked stick so that the flow can be estimated at various times of year. Find a tree, bridge, or post that will withstand the higher stream flows and affix your gauge to this stucture. This activity is an excellent homework assignment. Students can compare results and come up with an average value. Discuss the advantages of multiple measurements and how scientists use approximations during all investigations. How could you improve your stream discharge estimate? #4.3 Students know major sources of water, its uses and importance, and its cyclic patterns of movement through the environment. Return to
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