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Stream Flow INTRODUCTION
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Stream flow or discharge is the volume of water that moves through a specific point in a stream during a given period of time. Discharge is usually measured in units of cubic feet per second (cfs). To determine discharge, a cross-sectional area of the stream or river is measured. Then, the velocity of the stream is measured using a Flow Rate Sensor. The discharge can then be calculated by multiplying the cross-sectional area by the flow velocity.
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Stream flow is an important factor in the stream ecosystem and is responsible for many of the physical characteristics of a stream. Stream flow can also modify the chemical and biological aspects of a stream. Aquatic plants and animals depend upon stream flow to bring vital food and nutrients from upstream, or remove wastes downstream. Stream flow has two components. The first is flow velocity, and the second is the volume of water in the stream.
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Flow velocity is influenced by the slope of the surrounding terrain, the depth of the stream, the width Factors Influencing Flow Velocity of the stream, and the roughness of the substrate or • Depth of stream channel stream bottom. If the surrounding terrain is steep, then rain water and snow melt will have less time to • Width of stream channel soak into the ground and runoff will be greater. In an • Roughness of stream bottom area with level terrain, such as farm land, the rain water has plenty of time to soak into the ground and • Slope or incline of surrounding terrain there is less runoff. The flow velocity will also vary as the width or depth of a stream changes. For instance, if you squeeze a water hose with your hand, the flow velocity of the water increases. This is because you have reduced the area that the water must flow through, while the volume of water passing through the hose remained constant. The same thing happens in a stream when the stream channel changes in its width or depth. The substrate of the stream bottom also affects the flow velocity since water moves faster over a smooth surface than a rough surface. Flow velocity is greater when the stream bottom is comprised of sand and clay and lower when it is cobble, rock, and boulders.
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The volume of water in the stream is affected by the Factors Influencing Stream Volume climate of the region. Areas with more rain and snow • Weather or climate will have more water draining into surrounding streams and rivers. Seasonal changes affect stream • Seasonal changes volume as well. In the summer there will be less water in the stream compared to the winter. The • Merging tributaries number of tributaries that merge with a stream or • Human impact river contribute more water to the system, increasing the stream volume. Humans are also responsible for altering the volume of water in streams. Water is removed for consumption, industry, and irrigation. Roads and parking lots cover vast areas, preventing rain-water from soaking into the ground. Instead, the water is forced to run off into surrounding streams and rivers.
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Expected Levels Through careful monitoring, the typical discharge of many of our streams and rivers has been determined by using historical stream flow data. Much of this data is available from the USGS in printed form, or over the internet at the USGS website: http://water.usgs.gov/realtime.html Below is sample data from a station monitored by the USGS.
Stream flow data of the Missouri River at Hermann, MO Table 1: Stream Flow Statistics at Various Locations Location
Min (cfs)
Mean (cfs)
Max (cfs)
Mississippi River at Thebes, IL
85,500
310,000
725,000
Missouri River at Hermann, MO
28,500
107,000
382,000
2,800
18,000
46,900
593
1,300
3,160
Colorado River at Cisco, UT Hood River at Hood River, OR
Summary of Methods The cross-sectional area will be determined for a stream site using a tape measure and meter stick. Measurements will be made at equal intervals across the stream cross-section. Flow velocity will be measured using the Vernier Flow Rate Sensor at each of the intervals along the cross section. Using these measurements, the stream flow will be calculated.
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Stream Flow
STREAM FLOW Materials Checklist ___ computer ___ Vernier computer interface ___ Logger Pro
___ Vernier Flow Rate Sensor ___ measuring tape (15 m or 50 ft) ___ meter stick
Site Selection 1. CAUTION: Always follow safety precautions when entering the stream. If the water is too deep or swift, select another site. Never venture out into the stream alone without another person available to assist you in case of emergency. 2. Within a 50 meter stretch of the stream, select two sites that are as far apart as possible and are representative of the stream as a whole. Avoid sites with bends or breaks in the stream caused by rocks or sandbars. Try to choose a site where some flow can be observed. It is not necessary for both sites to be the same. One site Avoid stream-bends Avoid can have a swift flow similar to that found near logs and rocks a riffle. The second site can have a moderate or slow flow like that found after a pool. 3. At each site, you are going to take a cross section of the stream and measure its width and depth. Try to select a cross section that is shallow enough to measure depth with a meter stick and easy to cross. To measure stream flow using the Flow Rate Sensor, avoid sites where the stream depth is less than 10 cm (4 in).
Site 1
Avoid Sandbars
4. The Flow Rate Sensor is equipped with a 5 meter cable. This enables you to take measurements up to 4 meters away from the shore without carrying the computer out into the stream. If the stream is wider than 4 meters, first monitor flow from one bank, then have the person holding the computer switch to the other bank of the stream. This should reduce the chances of dropping the equipment into the water and damaging it.
Site 2
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Testing Procedure Measuring a Stream Cross Section
1. Using the measuring tape, determine the width of the stream cross section in meters and record that measurement on your Data & Calculations sheet (round to the nearest 0.01 m). Divide the cross section into six equally spaced sections. 1
2
3
4
5
6
Initial distance = 0
7
Final distance = Stream width Final depth = 0
Initial depth = 0
1 distance out
depth
2. Using the meter stick, measure the depth of the stream in meters at each of the equally spaced points along the cross section. Record the depth and the distance out from one shore edge, in meters, on the Data & Calculations sheet. Always measure from the same shore. Be sure to include both the initial distance and depth, and the final distance and depth. Measuring Flow Velocity
3. Position the computer safely away from the water. Keep water away from the computer at all times. 4. Plug the Flow Rate Sensor into Channel 1 of the Vernier interface. 5. Prepare the computer for data collection by opening the file “16a Stream Flow” from the Water Quality with Vernier folder of LoggerPro. 6. You are now ready to monitor flow rate. a. Place the Flow Rate Sensor at the same points the depth measurements were made in Step 2 (e.g., 1, 2, 3…). Since points 1 and 7 are on the shore edge where there is no flow, skip these points and perform flow measurements at the remaining five points. 1
2
3
4
5
6
7
b. Submerge the impeller of the Flow Rate Sensor to about 40% of the depth measured at each section. If the section is shallow enough, use the plastic risers that are included with the flow rate sensor to support the sensor on the stream bed. The risers make it easier to keep the impeller of the sensor in the same spot and oriented in the same direction.
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Stream Flow c. Point the impeller of the sensor upstream (as shown below) and directly into the flow. Click to begin to begin a 10 s sampling run. data collection Click Important: Leave the probe tip submerged for the 10 seconds that data is being collected. When the sampling run is complete, stop data collection and record the flow rate value on the Data & Calculations sheet.
40%
risers optional
Flow
7. Repeat Step 6 for each of the remaining four sections. 8. Repeat Steps 1–7 for the cross section at Site 2. Calculating Stream Flow
9. To calculate the stream flow, open the file “16b Stream Flow” from the Water Quality with Vernier folder of LoggerPro. Enter the distance out values in the first column and the depth in the second column: a. To enter a number in a column click in the first cell of the first column, labeled Distance Out. Type the distance out values recorded on the Data & Calculations sheet pressing the down arrow key after typing each value until you have entered all the distance out data. b. When the distance out data has been entered, click on the first cell in the second column, labeled Depth. Enter the depth values that were recorded on the Data & Calculations sheet by typing in the value and pressing the down arrow key after typing each value until you have entered all the depth data. 10. You are now ready to obtain the integral for the data you entered in Step 9. To do this, click on the Integrate button, . The integral value is displayed in the statistics box on the graph. Record this value on the Data & Calculations sheet. 11. Repeat Steps 9–10 for Site 2.
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DATA & CALCULATIONS Stream Flow Stream: ___________________________________
Time of day: ____________________________
Site name: _________________________________
Student name: __________________________
Site number: _______________________________
Student name: __________________________
Date: _____________________________________
Student name: __________________________
Site 1 A
Width
(m)
B
Distance
(m)
C
Depth
(m)
D
Cross-sectional area
(m )
E
Flow velocity
(m/s)
F
Average velocity
(m/s)
G
Stream flow
(m /s)
1
2
3
4
Site 2
5
6
7
0
1
2
3
4
5
6
7
0
0
0
0
7
1
0
2
1
—
2
3
4
5
6
2
3
4
5
6
— —
7
—
3
(Optional) Convert Stream flow to cubic feet per second H
Stream flow
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(ft /s)
Row Procedure: A. Record width of stream using a measuring tape. B. Record the distances out from the shore line. C. Record depth of stream using meter stick. D. Record calculated cross-sectional area from Step 10. E. Record flow velocity of each column measured with Flow Rate Sensor. F. Average velocity = SUM E ÷ 5 G. Stream flow = D X F H. Cubic feet per second = G X 35.32 Field Observations (e.g., weather, geography, vegetation along stream) ___________________________ ____________________________________________________________________________________ Test Completed: ________________ Date: ______
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Vernier Lab Safety Instructions Disclaimer THIS IS AN EVALUATION COPY OF THE VERNIER STUDENT LAB.
This copy does not include: z
Safety information
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Essential instructor background information
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Directions for preparing solutions
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Important tips for successfully doing these labs
The complete Water Quality with Vernier lab manual includes 16 water quality tests and essential teacher information. The full lab book is available for purchase at: http://www.vernier.com/cmat/wqv.html
Vernier Software & Technology 13979 S.W. Millikan Way • Beaverton, OR 97005-2886 Toll Free (888) 837-6437 • (503) 277-2299 • FAX (503) 277-2440
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