Floodplains in the field (with GIS)

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
• Utilizing available GIS resources to add spatial context
• Collect GPS data to create digital archive of observation sites

Skills

• Surveying (this original element is also a GIS skill)
• 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
• Creating local maps from online GIS or desktop GIS resources
• Using GPS receivers to locate field observations sites

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). How to use a GPS receiver.

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. A clear view of the sky (limited hills & tree foliage) is helpful if you plan to use GPS.

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)
• GPS receiver(s) - one or more (WAAS-enabled consumer handheld receivers are sufficient for this lab)


• Students should bring field notebooks and pencils. If they have created maps of the area before the lab they should bring the print-out(s) to the lab to mark their observation locations.

Sample lab notes using GIS (Microsoft Word 40kB Feb22 05) -- Instructions are provided to incorporate GIS and GPS options into the field experience. GIS elements are noted with superscripts for easy editing depending on what resources are available.
Original sample lab notes (Acrobat (PDF) 88kB Mar10 04) (without GIS)

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.

Determine what maps you would like the students to create before the lab and how they will create them (data source, scale, etc.). Online sources such as the USGS/Microsoft Terraserver site produce topographic maps and aerial photos. Otherwise the data resources and default map file should be created in advance if desktop GIS software will be used before or after the lab. The GIS version of the sample hand-out notes provides basic instructions on each GIS and geologic aspect of the lab. The file can be edited to remove any components that are not feasible within your goals/resources for the lab. Students may require additional instructions on downloading image files from the web and inserting the images into word-processing software.

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. This is especially useful if you will have the students develop local topographic maps before the lab.

A primer on how to use the handheld GPS unit is useful. Generally it takes the students about 15 minutes with the GPS receiver to start recording tracks (breadcrumb trails) and waypoints with comfort. Downloading the GPS data can either be part of the student exercise or done by the instructor to create a single compilation of the GPS records. Students with little computer experience may find the downloading process intimidating.

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. Include annotated maps marked with the locations of the field observations.

Follow this link (Microsoft Word 40kB Feb22 05) for GIS-enhanced lab notes. GIS elements are noted with superscripts for easy editing.
Follow this link (Acrobat (PDF) 88kB Mar10 04) for original lab notes without GIS.

Also see the following resources:

• Creating Maps with Terraserver - download JPG files of USGS topographic and aerial photos from almost anywhere in the U.S.
• Using Handheld GPS Receivers - an overview of how to collect data with inexpensive handheld GPS units