Cutting Edge > Sedimentary Geology > Sedimentology, Geomorphology, and Paleontology 2014 > Teaching Activities > Lag to peak with a stream table

Lag to peak with a stream table

Amanda Schmidt, Oberlin College
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This page first made public: May 27, 2014

Summary

Students use a small stream table in groups to investigate how channel form determines the shape of the hydrograph (including lag to peak). They use three channels: no channel (just sediment filling the table), a "concrete" channel (straight, no sediment on bottom), and a meandering channel. All channels get the same water input and students measure the amount of water that comes out to make a hydrograph.

Context

Audience

This is used as a lab exercise the week we study hydrology in a required Earth Surface Processes class where the only pre-requisite is Physical Geology. Students range from first to fourth year.

Skills and concepts that students must have mastered

Students should know what hydrographs are and what lag to peak is.

How the activity is situated in the course

This is the weekly lab assignment for hydrology week.

Goals

Content/concepts goals for this activity

Higher order thinking skills goals for this activity

Other skills goals for this activity

Description and Teaching Materials

Students have played with the stream table before in my class, but if they haven't, it is worth giving them some time to do that. I am generally working with two lab groups of 3-4 students. In each group, one person will write the lab report, one will edit it, and one or two will do a concept sketch using the results of the lab. Ideally you'd have an hour to an hour and half to do all of this, particularly if they haven't used the stream table before. With a longer lab, they could make the hydrographs in lab.

Students arrive and I have them determine a flow rate for the water coming in to the stream table. They decide on an input volume, rate, and time to aim for. It doesn't matter much what this is, as long as it is consistent for all trials. They also should determine how frequently they will measure water coming out of the table (we did 20 seconds into a 1 L graduated cylinder for 4 L of water coming in in 20 seconds). They should practice collecting the water and reading volumes out at the intervals determined. It takes a little coordination between the student with the stop watch, the recorder, and two with graduated cylinders (so they can switch back and forth).

They then make one of the three channel forms (either no channel - just sediment, a "concrete channel" (straight and with sediment pushed to the sides), or a meandering channel with sediment on the bottom). They wait for water to stop dripping out the end of the table.

After the table is ready, they turn on the water for their pre-determined input volume and time. Students at the end of the table collect water and read out volumes to the recorder. Keep collecting data until very little (or no) water is coming out of the table.

This is repeated for each of the three channel types. You could add more channel types or different input hydrographs.

Students make hydrographs showing the volume of water that came out in each interval of time (say 20 seconds). They then complete their assignment for the week (write the lab report, edit the report, or make a concept sketch).

This basically models a pulse flood from upstream (say a dam burst) and how different channels respond differently.
Lab handout (Acrobat (PDF) 262kB May27 14)



Teaching Notes and Tips

We happen to have an EmRiver Em2 stream table, but any would work. We only have one so I have the students come in groups of 6-7 (8 would be ok) for a 45 min session to work with the stream table.

Assessment

I grade their lab reports, edits to the lab report, and concept sketches using the same rubric I use all semester.

References and Resources

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