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Floodplains in the field

Mary Savina, Carleton College, msavina@carleton.edu
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This material was originally developed as part of the Carleton College Teaching Activity Collection
through its collaboration with the SERC Pedagogic Service.

Summary

In this lab, students measure a topographic and geologic cross-section across a floodplain by simple surveying and augering techniques.

Learning Goals

Goals

  • Observing fluvial landscapes in detail
  • Connecting landscape observations to map and cross-section representations
  • Relating earth materials to landscape position and geomorphic process
  • Moving between cross-sectional and planar views of landscapes
  • Reconstructing history of a river system
  • Understanding rivers as transporters and depositors of sediment

Skills

  • Surveying
  • Coring and describing alluvial material
  • Understanding vertical exaggeration in cross-sections
  • Making a sketch map
  • Observation, note-taking, and sketching
  • Describing color and texture of soil materials

Context for Use

This lab can take from one to three hours, depending on the detail and methods of the surveying, drafting of the cross-section and maps, and number of soil cores dug.

Physical geology or geography course: Use during units on rivers, fluvial landscapes, or sedimentary processes
Earth History course: Use during unit on how geologic landscapes evolve
Earth systems science course: Use during discussion of storage and transport of water and sediment in river systems

Useful background information before lab: Distinguishing sand, silt, clay (although this can be taught during this lab).

Field site: a stream or river with a floodplain, ideally undisturbed by humans. It is helpful, though not essential, to have good visibility across the floodplain.

Equipment needed:

  • 50-meter tapes
  • Augers or other soil-coring devices (a meter in length is helpful)
  • Automatic level, tripod and survey rod - or a handlevel in the hands of two students of equal eye height
  • Graph paper (five to a cm) for each student
  • Oversize sketchpad and markers
  • Compass
  • Soil color book, texture triangle and tips on distinguishing sand, silt, and clay (optional)

  • Students should bring field notebooks and pencils

Teaching Materials

View Sample lab notes (Acrobat (PDF) 88kB Mar10 04).

Teaching Notes and Tips

Scout the area ahead of time to locate a place for the topographic profile and soil cores that has these characteristics: approximately perpendicular to the river and floodplain margin, reasonable visibility along the line, typical of the area.

Students will expect that the local slope across the floodplain will be from the floodplain margins toward the river. On unmodified floodplains, with streams that overtop their banks every other year or so, the topographic profile will contain a higher area adjacent to the stream channel (the levee). It's common for the lowest part of the floodplain to be near the margins, not near the river. You can start the lab indoors by asking students to draw their conception of what the topographic cross-section will look like, and then return to those sketches at the end of the lab period (or a subsequent class period) to compare their conceptions with reality.

Assessment

For a self-contained lab (no homework required): Use oral reports from groups to assess how well they interpreted their part(s) of the assignments.
At the start of the next class period, ask students to sketch the topographic cross-section and briefly describe the materials in each section and how they formed as an informal writing assignment and/or quiz.

Assessable homework after the lab: Drafted explanatory cross-sections and maps; soil stratigraphic columns, short paper about the relationship between river evolution and the stratigraphy and topography of the floodplain.

References and Resources

Follow this link (Acrobat (PDF) 88kB Mar10 04) for lab notes.

Also see the following print and web resources:

Under construction

Subject

Environmental Science:Ecosystems:Biogeochemical cycling, Geoscience:Geology, Hydrology:Surface Water

Resource Type

Activities:Field Activity

Special Interest

Field-Based Teaching and Learning

Grade Level

College Lower (13-14):Introductory Level

Ready for Use

Ready to Use, Meets Peer Review Standard:Anonymous Peer Review

Earth System Topics

Biosphere:Ecology, Solid Earth, Hydrology, Surface Water

Topics

Energy/Material cycles, Hydrosphere/Cryosphere:Surface Water, Earth surface, Time/Earth History

Theme

Teach the Earth:Course Topics:Biogeoscience, Teach the Earth:Teaching Environments:Intro Geoscience, Teach the Earth:Course Topics:Environmental Science, Hydrology/Hydrogeology, Teach the Earth:Enhancing your Teaching:Teaching in the Field, Teach the Earth:Teaching Topics:Water