NAGT > Teaching Resources > Teaching in the Field > Field Trip Examples > Bedform Mapping in a Coastal Environment

Bedform Mapping in a Coastal Environment:

Peter Lea, Bowdoin College

Intended Audience: This activity is designed for an undergraduate majors course in sedimentary geology.

Location:

Although specific to the mesotidal barrier setting in coastal Maine, the exercise and its approach may serve as an example that can be adapted to other settings. I do this exercise in an area in southernmost Reid State Park, Maine (see downloads for map).

The exercise takes about 3 hours in the field, and is of course tide-dependent. Given the timing of tides during the course, I either run it as an extended afternoon lab session or a half-day weekend field trip. I try to introduce briefly students to examples of bedforms at the beginning of the trip, checking that they know what measurements to make and how to use the equipment (GPS units and digital cameras). I encourage a simplified classification of transverse bedforms (e.g., 2-D vs. 3-D; straight vs. sinuous), trying not to get them bogged down in subtle distinctions. When they encounter bedforms that are unfamiliar to them from class (e.g., rhomboid ripples, ladderback ripples), I encourage them to take photographs and refer them to textbook descriptions (e.g., Reineck and Singh, J.R.L. Allen) following the next class.

Summary:

During this 3-hour exercise, students use a learning cycle of prediction-observation- comparison to investigate diverse bedforms exposed at low tide at a beach/inlet/tidal-delta complex and to relate them to formative flows.

Context:

To prepare for this activity, students receive background on bedforms and flow regimes in class and practice identifying and classifying bedforms from field photographs. Students are then given a map of a barrier beach/inlet/tidal delta complex in mid-coast Maine and asked to predict what bedforms they expect to find in specific sub-environments. During a subsequent field trip to the area, students observe, classify and map bedforms and relate them qualitatively to formative flows. Qualitative description and classification are supplemented by quantitative measurements of bedform morphology and orientation, and by GPS-located digital photographs. After the trip, students compare their predictions and observations of bedforms in the sub-environments, reflecting on the reasons for the differences and the evolution of their thinking. The exercise also serves to set the stage for subsequent quantitative studies of bedforms and bedload transport, as well as interpretation of sedimentary structures and clastic depositional environments in the geological record.

Goals:

The activity gives students direct experience in recognizing, describing and mapping bedforms and relating them qualitatively to formative flows. Students become familiar with a diversity of bedforms within lower- and upper-flow regimes, as well as ripples formed by waves and by wind. During the prediction exercise, students essentially make hypotheses based on their current understanding of bedforms (i.e., without direct field experience). By comparing their predictions with observations and reflecting on differences, students critically evaluate their evolving understanding of bedforms and flows. Students also gain experience with GPS units and digital cameras, and learn how to take effective field photographs of bedforms.

Assessment and Evaluation:

Evaluation comprises checking field descriptions for accuracy and completeness, as well as reviewing students' assessments of the differences between their predictions and observations. Such comparisons commonly allow me to track the evolution of student's thinking, such that I can reinforce conceptual advances and/or correct persistent (or new) misconceptions. Asking for a synthesis of major flow patterns evaluates whether students can recognize the larger picture ("forest") from compilation of the details ("trees").

Materials and Handouts:

See more Field Trip Examples »