Lesson Plan on Lake Levels

The U.S. Corps of Engineers publishes hydrographs for the Great Lakes.  These water level versus time plots, available on the web, show by month which years are all-time records for maximum and minimum water surface levels.  A curve is also displayed that shows the monthly, average surface levels constructed from historic records.  Finally, the Corps gives a prediction of what the water level will be for the next six months.  These curves are an excellent resource to help students understand the expected fluctuations of lake levels, both seasonal and longer term variations.  To choose any Great Lake to use for this exercise, go to Great Lakes Water Levels and select a lake.  The exercise below uses the graph for Lakes Michigan-Huron.  (The Corps lists the lakes together as their surfaces are at the same level.)  If you want to work with Lakes Michigan-Huron, you can go directly to Lake Michigan-Huron

Example Exercise

1. Aside from the month of January, what year was Lakes Michigan-Huron at its all-time maximum level? ____________

2. What was the maximum fluctuation in lake level that year (to ±0.1m)? ____________

3. What year was Lakes Michigan-Huron at its all-time minimum level? ____________

4. What was the maximum fluctuation in lake level that year (to ±0.1m)? ____________

5. The variation in the lake levels on an annual basis appears to be cyclic.  Explain why that might be the case.  Use the average curve (1918-1998) to determine during which season the lakes appear to be the highest. ____________________ In your discussion indicate why you think that that is the case.

6. Why might the minimum lake level curve have less of a fluctuation (see your answer to question #4) than the maximum lake level curve (see your answer to question #2)?

7. What does the Corps predict the lake level will be three months from now? _________ (Be sure to include their estimated “error bars”.)  Study how the Corps drew the curve and error bars for their prediction.  Now try your hand at predicting lake levels!  Of course, you do not know what the weather will be like in the next year, but you still can make an educated guess as to what the lake levels will do over the next year.  So extend the Corps prediction and error bars.  What do you predict the lake level will be seven months from now? __________________ (Include your estimated error bars.)

8. What is the maximum difference between the all-time high and all-time low lake levels  (to the nearest ±0.1m)? ______ How many feet is that (to the nearest foot)? _____ How many years did it take for the lakes to vary by that amount? ___________

9. How much do the lake levels fluctuate over an average year (to the nearest 0.1m)? __________ What was the maximum lake level fluctuation for the past year (to the nearest ±0.1m)? __________ Are the values you obtained by examining the two different plots significantly different?  If so, what explanation do you have for the difference in the all-time, average fluctuation over a year versus the fluctuation we have observed in the past year?

10. In the last several years many lakeshore homeowners have complained about the fluctuations of lake levels and problems the fluctuations have caused for them due to beach, bluff, and dune erosion.  Now boat owners are complaining that the lakes are so low that some cannot get their boats safely into the lake. Based on your answers to questions 8 and 9 above, what might you tell these people that they can expect in the future concerning lake level fluctuations and accompanying erosion and navigation problems?

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LIVING WITH THE GREAT LAKES
BROUGHT TO YOU BY:
GRAND VALLEY STATE UNIVERSITY
DEPARTMENT OF GEOLOGY
ALLENDALE, MICHIGAN 49401