Graphing Tides
Integrated Science 1
Redwood High School
10/14
Name:
Period:
! Background
The level of San Francisco Estuary is constantly changing. In fact, these regular and predictable fluctuations occur all
around the globe and are called the tides. The tides are so predictable that daily tide tables are available for an entire
year and may actually be calculated years in advance. The daily, monthly, and seasonal tidal patterns of the San
Francisco Estuary are absolutely critical in the overall ecology of the bay. The tides influence the salinity in all parts
of the estuary, which limits the types and numbers of organisms, which may exist in any particular area.
In this activity, you will use tide tables for a single month as your data. This data will then be represented in
graphical form for a clearer and more visual analysis. Individuals will produce a short-term graph (1 week). Which
may become part of a group graph which will represent one month of tidal patterns.
! Focus Questions
• What is the nature of the daily, and monthly tidal cycles?
• Why do the tides change on daily, and monthly cycles?
• What are the major effects of these tidal fluctuations on the bay/estuary?
! Procedure
1. Working individually use the provided graph paper to graph the tidal patterns from the tide chart provided. Each
student will be assigned/graph one week of the month.
Tide Table Information: Corte Madera Creek; October. WEEK:
1!
2!
3!
4!
2. Use the tide table provided to collect the data for your week.
3. Because each graph may become be part of a larger group graph, you MUST accurately follow the set-up
instructions for the graph.
4. Plot your points in pencil.
5. Record on the graph the correct height and time of each high and low tide during your week period. Connect the
data points with a straight line.
6. Record on the graph the appropriate phases or percent of the moon for your study period. (See tide chart)
7
If instructed, connect your completed graph in the correct sequence with the other graphs in your group.
8. Use your graph to answer the discussion questions.
! Discussion/ Conclusion
1.
Describe the tidal pattern of your graph (what does your graph look like?)
2. a) Tidal Range is the difference, in feet, between high and low tide. Note the date and the height of the largest
and smallest tidal ranges during your week.
Largest Tide Range: Date:
High Tide:
Low Tide:
Diff:
Smallest Tide Range: Date:
High Tide:
Low Tide:
Diff:
b) What is the phase of the moon for those tides?
Largest Tide Range: Moon Phase - or - Moon Percent:
Smallest Tide Range: Moon Phase - or - Moon Percent:
3. Record the definitions for spring and neap tides (either from your notes or from your Earth Science Textbook).
Then indicate on the chart which is spring tide and which is neap tide.
Spring Tide:
Neap Tide:
3. Specifically, how are the tides influenced by the moon?
4. As a result of the daily tidal cycle what particular problems are faced by organisms that live in inter-tidal areas
such as mudflats and tide pools? How might these problems be different during the rainy season?
5. (Think!) The scientific term for the point of meeting between fresh and salt water is the "null zone." Describe
what you think occurs in a null zone physically, and for the organisms that live there.
2
Graphing Tides
Tide Chart Information:
Graphing Tides
Month:
Name:
Year:
Period:
Location:
 Directions: Each group of four boxes on the X-axis represents a period of 24 hrs. Label each day by noting 12a (midnight) 6a, 12p, 6p, 12a on the X-axis.
Label the Y-axis (in feet) from –2 thru 8. The date of the month should be recorded in the space provided below each set of times. Using a pencil, record the
relative height of both the low and high tides for each day. Connect all the data points with a straight line. Finish your graph by drawing the phases of the moon
in the space provided.
Moon Phases - or - Percent
Date