Problem: How can you make rough estimations for velocity and discharge rate in a flowing stream?
Processes: observation, measurement, analysis, calculation
Materials: meter stick, stop watch, float
Elicitation questions: Does a stream always flow at the same rate? What affects the rate of flow?
Procedure: A stream next to a school gives an earth science teacher an excellent opportunity to do field work. Just walking along the stream allows one to point out principles discussed in class, such as erosion and deposition as they relate to water velocity, braided stream, meander, etc. A quantitative lab, such as rate of stream flow allows a student to practice science by observing, collecting, analyzing, computing, and reaching conclusions.
A meter stick, stop watch, and a float (ping pong ball) are all that is needed for a student or a small group of students to measure flow. have the students pick a small stretch of the stream where it runs fairly straight. Have the students find the depth of the water at 6 equally spaced locations across the stream. We have to make an assumption that the stream is like a rectangle. The average of the 6 depths will serve as the height of the rectangle. the distance across will serve as the width.
Measure 2 meters upstream from the 6 depth sites (2 meters will be the length). The volume of the rectangle can be calculated by Vol= I x w x h. Next, place the float and time how long it takes to travel the 2 meters. The velocity of the stream is found by dividing the 2 meters by time (v =D/T). We will assume that the water moved uniformly through the stream bed. Thus, the volume that we calculated for that section of stream would be the volume that flowed during that time. To find discharge per second, divide the volume by the time. You can then ask the students: How much water flows per year?
This lab can be conducted a few times per year to show that stream velocity is influenced by depth and width as much as inclination. Compare seasonal differences.
Application: Realize the danger of flash floods.
Evaluation: hand in lab sheets with all data, calculations, and conclusions.
1. 1. ____________________________________
Total / 6= average height Total / 6 average depth
length = 2 meters
Volume = I x w x h
Time = __________________________
Velocity of stream = 2 m/time in sec 2 m/sec.
Discharge rate = vol / time = ________________________
How much water flows in a year?