Graphing Tides

Martin B. Farley, University of North Carolina at Pembroke
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Student graphing of high and low tide from locations showing the three tide types (diurnal, semi-diurnal, and mixed) and the Bay of Fundy (tidal amplitude increased by resonance). Students recognize that not all tides are the same and that location is an important control on tides.

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Two courses:

  • Introductory-level oceanography--students graph all four locations and make simple interpretation. Generally, the students taking the course are junior/senior science education or science majors.
  • General education earth science--pairs of students get one location each. Then I have groups report results that I summarize on board.

Skills and concepts that students must have mastered

Basics of tides (at least how equilibrium tidal theory produces two tidal cycles per approximate day).

How the activity is situated in the course

This is an exercise that follows basic description of tidal forcing (this is more elaborate in Oceanography than Earth Science).


Content/concepts goals for this activity

Variability of tides (number of tides/day and range) despite the apparently simple global forcing.

Higher order thinking skills goals for this activity

  • Evaluation of the global tidal forcing versus actual local conditions.
  • Pattern interpretation from graphs.

Other skills goals for this activity

A main point of the exercise is to give students practice in making graphs. My students' graph skills are rudimentary, even for the upper-level Oceanography students.

Description and Teaching Materials

The activity uses four files:

  1. Graphing Tides.docx (Microsoft Word 2007 (.docx) 14kB May30 13) -- the student worksheet
  2. Tides Exercise.xlsx (Excel 2007 (.xlsx) 84kB May30 13) -- tidal data, including sheets to print as data handouts for students, graphs of the data (often useful to project after students have graphed), and supporting information
  3. Graphing Tides solution set.docx (Microsoft Word 2007 (.docx) 15kB May30 13) -- answer key for the student worksheet
  4. Graphing Tides instructor notes.docx (Microsoft Word 2007 (.docx) 18kB May30 13) -- guide to use including discussion of graph paper, helpful hints, and data source.

Teaching Notes and Tips

See instructor notes document.


I grade the lab handout.

In addition, I have a dominantly diurnal location (included in data spreadsheet), where a couple of shoulders occur on the diurnal transition to low tides. These are the semi-diurnal forcing peeking through. I use this on exams. I ask students to graph the data and identify the dominant tidal type. Then I ask if there anything different from the dominant type and what it might suggest to get them to reason what is going on.

References and Resources

I get my tidal data from the WWW Tide and Current Predictor: