Investigating Stream Energy and Gradient Using Small Stream Tables
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In this activity for a Physical Geology Lab, students investigate the relationship between stream energy and stream gradient using small stream tables. Students manipulate stream processes of sediment erosion and deposition by changing the gradient of their stream. Students will create hypotheses about stream processes and test them by observing stream behavior. Students compare and contrast their small stream models to real streams, emphasizing the ways in which the model does and does not approximate real life. Assessment is based on a series of questions and diagrams that students will complete.
Students will gain an understanding of how gradient affects stream channels and erosion. Students should practice observation and interpretation of stream processes in this lab activity. They should also develop communication skills by describing and drawing their observations. Students should synthesize information learned in lecture class with laboratory observations. Students need to think critically about the ways in which the streams do or do not mimic real life. They also practice critical thinking by developing hypotheses about how the stream will behave, and explanations of why and how they were correct or incorrect. Lastly, students practice teamwork by completing this activity in groups.
Methods of Geoscience In this activity, students create a small model of a stream system, then change the gradient of the stream to investigate the relationship between gradient and stream energy. This lab addresses the methods of geoscience through development and testing of a hypothesis, making observations of natural processes, and developing and understanding of the limitations of using models to investigate the Earth. Students practice critical thinking and synthesis of concepts from lecture and lab.
Context for Use
This activity was designed to be used in a Freshman-level Physical Geology class at a community college. It works best in classes of 30 students or less, working in groups of three or four. Students should have an introduction to basic stream processes (stream gradient, energy level, braided and meandering streams, sediment loads, etc) before they begin the lab. This activity usually requires about 1.5 hours in a laboratory class. It could easily be adapted to other grade levels by changing the questions asked about the streams. I plan to revise this lab to include more inquiry-based learning for future semesters. With more sophisticated stream tables, this activity could be adapted to higher level classes, but with the stream tables used, it would be better used for early college or lower grade levels.
Description and Teaching Materials
During this lab, students start with a low gradient stream, and increase the gradient in three steps. At each step, they observe the type of stream channel formed, and record where the most erosion occurred. They also carve a meandering channel for the low gradient stream, and watch for erosion and depostion at cutbanks and pointbars. During this part of the lab, it is important that the students watch their streams carefully, because the water flows relatively quickly along the stream path. Students calculate the gradient of the stream at its highest and lowest gradients. They also answer questions about the sediments deposited in the "lake" at the bottom of the stream. Lastly, students compare and contrast their streams to real streams.
Materials needed for this lab (see attached assignment as well): LabAids® stream tables and sediments (although home-made ones could be used as well), rulers, notebooks, string (for easy measuring of stream length), cups, water, colored pencils.
Teaching Notes and Tips
This lab works best when students have already covered stream processes in lecture class. I start this lab activity with a review of basic stream processes and terminology. In particular, I review how stream energy changes along a stream profile from the headwaters to the mouth, and how the stream channel, path, and sediment load will change along the profile. This material will have already been covered in lecture class. I also demonstrate the set-up of the stream tables and introduce the different parts of the stream tables.
Students complete a worksheet with questions about the lab activity. This lab is assessed by a point system: each question is worth a certain number of points (more points for diagrams and critical thinking questions, and fewer points for direct observations). This assessment system could easily be modified to another format. Although students work in groups, each individual turns in a completed worksheet with his/her own observations and explanations.
References and Resources