How Do Tides Work?
ES2406  Making Observations and Predictions with a Tide Chart

The table below shows predicted tide information for Cape Porpoise Harbor, Maine for the month of October, 2001. Tables like this are generated for locations all along the coasts of the U.S. The charts for each site may be very different, even for locations that are quite close to each other. This is because tides vary according to the shape and depth of the body of water as well as to the geographical location.

Tide heights in the table are compared to the average low water level for that location. A negative tide height indicates the water level will be below the average low water line.

  !   Examine the tide table to answer questions 8 and 9 below.

Tom Grace, TERC, Adapted from:
Tide table for Cape Porpoise Harbor, Maine — October 2001

8. Did the high tides occur at the same time on Oct. 17 and Oct. 24? Why or why not?

9. Predict the changes in tide levels you would have seen at Cape Porpoise Harbor October 31, 2001.

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