Summer Research Program for Science Teachers

Park West High School, Manhattan

Determining the Discharge Rate of a Meandering Stream

Background information

Students should understand basic stream dynamics and how meanders affect the velocity and bottom profiles of different locations across a stream. [9-12 Content Standard D- Geochemical Cycles]

In this investigation students will learn how to determine the discharge rate of a stream at a given point.  They will also construct a bottom profile after predicting the shape.  They will utilize graphing and mathematical skills to solve other unknowns.  They will also design an experiment to confirm their solutions.

Problem:

Aim:  How does a streams shape and bottom profile determine the discharge rate at a given point? [9-12 Content Standard A- Understandings about scientific inquiry]

Materials:

Pen/Pencil, Ruler (cm)

Calculator, Flow meter: (For instructor Demonstration).  If not available see the following web site: http://www.globalw.com/flow.html

Procedure

Your team has been selected to determine the rate of discharge for a stream that is running past an old herbicide/fungicide plant. Remember, discharge is the amount of water that passes by a given point over a given time period.   Arsenic, a ubiquitous metal that has been determined to be a carcinogen, has been found in the soil and is believed to be leaching into the nearby stream.  The information that you determine in this lab will be essential in further understanding arsenic mobilization. [9-12 Content Standard F- Environmental quality, Natural and human induced hazards.]

Objectives:

In the activity below, you will gather information enabling you to determine the discharge of a stream at a given location.  The diagram below represents a map view of the stream you are investigating.  Arrows indicate direction of stream flow and leaching groundwater direction.

Materials:  Pen/Pencil

Ruler (cm)

Flow meter (Demonstration)

Calculator

Procedure:

(1)   Examine the above stream map.  Based on your knowledge of meandering streams, sketch profiles for locations A through C below.

 A

(2)   Now use the data table below from section B – B’ to determine the area and discharge for each flow meter reading.  Fill in the information in the boxes below.  Remember;

Area = Depth x Width

Discharge = Flow rate x Area x 1000.  (1000 is used for converting to liters)

 Distance from B Depth Width of section Area Flow Rate Discharge (meters) (meters) (meters) (meters^2) (meters/second) (liters/second) B 0.00 0.00 0.25 0.00 0.50 2.00 0.50 0.22 1.00 3.00 0.50 0.43 1.50 3.50 0.50 0.64 2.00 3.50 0.50 0.62 2.50 3.00 0.50 0.42 3.00 2.50 0.50 0.35 3.50 2.00 0.50 0.26 4.00 1.50 0.50 0.15 4.50 1.00 0.50 0.10 5.00 0.50 0.50 0.07 5.50 0.25 0.50 0.03 B' 6.00 0.00 0.25 0.00 Total Discharge = l/s

(3)   Use the Distance and Depth measurements from the above data table to construct a graph of the bottom profile of the stream at location B.

(4)   At which distance from point B is the discharge quantity the greatest?  Explain why.

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Total Area (from table) = ______________

(6)   Now, determine the total area of the stream along profile B-B’ by counting the total number of boxes.  Each box is 0.5 meters, so when you are finished you need to divide this value by 4 to determine the area in square meters.

Total Area (counting boxes) = __________

(7)   Determine the percent deviation between your two total areas.  Use the area from the data table as your accepted value.

Percent Deviation =  ________________

Questions:

(1) When would the method of counting boxes be a more accurate method of determining the area of a stream?  Explain.

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(2) Can you design an experiment that would help confirm your answers of total discharge quantity?  Explain.  (Hint:  discharge is in liters per second) [9-12 Content Standard A- Design and conduct scientific investigations]

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(3) At what location along the stream will arsenic probably be found in the highest concentration?  Lowest concentration? [9-12 Content Standard B- Motions and Forces]

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(4) Can you suggest any methods for preventing arsenic from leaching into the stream and contaminating nearby surface water?  Be creative. .  [9-12 Content Standard F- Natural resources, Environmental quality, Natural and human induced hazards, Science and technology in local, national, and global challenges.]

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(5) Does your preliminary stream profile of B-B’ resemble your graphed profile?

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Analysis and Conclusions

At this point discuss how pollutants may enter the stream and discuss the implications of a nearby reservoir.  Review the student’s suggestions for preventing the arsenic from leaching into the stream. [9-12 Content Standard F- Natural resources, Environmental quality, Natural and human induced hazards, Science and technology in local, national, and global challenges.]

Assignment:

Have students research similar occurrences of arsenic leaching into water systems.  Have students identify various locations in the world where arsenic is a problem.  Also, have them research the biological affects on the human body of arsenic exposure.  [9-12 Content Standard F- Environmental quality, Natural and human induced hazards.]