Understanding Tide Gauge Data
Lesson 3 of 10
Objective: SWBAT plot and compare tide data for two locations and analyze the data for patterns.
Before starting this lesson you may want to teach or review the cause of tides. NOAA Ocean Service Education has several lessons you could use or you may have one you like. Whichever you choose, you should at minimum review the concepts of tidal motion and forces.
In this activity, students learn how scientists monitor sea levels around the world. Tide gauges are used to take measurements of sea level; some tide gauges have been recording sea level for over a hundred years. Students learn about acceleration of sea level rise and how it affects people in different parts of the country. Students then compare the threat of sea level rise in Florida to other places in the United States where the sea level is also rising.
- NOAA Tide Gauge Tutorial ...watch this before first in order to familiarize yourself with the process of getting data from the NOAA Tide and Currents website.
- Dry erase markers
- NOAA Tides and Currents (link for tide gauge data)
For an opening activity, have copies of the article Introduction to Storm Surge and the student worksheet to complete.
Assign the reading and ask students to use the article to complete the worksheet.
I have created this worksheet to follow the reading and pull key pieces related to the remainder of the lesson.
Note: Since the reading contains so many color graphics and I have limited access to color copying at school, I assign this reading the night before as homework and make the reading available online through my class website.
I ask my students to share their responses in their lab groups and discuss any discrepancies in their answers. I make myself available at this time to talk with small group of students and help them think through any parts they are struggling with.
Put your class into groups of 3-4 students. Each group looks at tide gauge data for Key West, Florida and Boston, Massachusetts.
Begin by showing your students the NOAA Tide Gauge Tutorial.
Have them get computers and handout the instructions for collecting data along with all the other materials needed.
Project the website and walk through the process of collecting the data for part 1. Once you students get the hang of it, turn them loose to work and move around to assist where needed.
While this lesson focuses on Florida and Massachusetts, you could change these to reflect cities in your area or of interest to you.
Here are two sample graphs from the activity.
After students complete the questions for analysis, engage them in a whole group discussion on their ideas.
You students may struggle a bit with making sense of data, so take the time to go over the conclusion questions and dialog with your class. You will want to discuss why the tides depths vary closer towards the poles as compared to locations closer to the equator. Also, the local topography has much to do with the tide as well. Be sure to push students thinking towards considering these variables.
Near the equator tidal influence is the lowest. This is related to the geometry of the moon's orbit in relation to earth, and the tilt of the earths axis.
Consider the plane of the earth's orbit around the sun as a fixed plane. This is known as the ecliptic. The earth's axis is on a tilt of 23.5 degrees to this plane, which is the tilt that produces the seasons. Also because of this tilted axis of rotation, there is a more pronounced effect of both the sun and the moon's tidal force at middle and higher latitudes.
Keep in mind that regardless of these general variations in tide, the local shape of a bay will have more effect on tidal height than lunar declination.
Students will answer the questions below as part of the investigation. Take time to discuss their findings.
Additional sites that may be helpful:
Follow Up the investigation with the following questions:
Q: What did both locations have in common?
A: The sea level has gone up in both locations.
Q: What does the slope of the plot tell you? What does it mean when the slope is higher?
A: The slope of the plot shows how fast a change is happening. When the slope is higher it means that the change in sea level is happening faster.
Q: Which graph had the highest slope?
A: The graph that had the highest slope is Boston.
Q: What was different about the tide gauge readings in Boston, MA compared to Key West, FL?
A: The sea level is rising faster in Boston, MA than in Key West, FL
Q: Look at the plot of Boston, MA. What is happening with the slope as time goes on? What does this mean about sea level rise in this area?
A: Yes, it looks like the slope is increasing over time, especially after the year 2000. The sea level is rising faster as time goes on.
Q: Look at the plot of Key West, FL. What is happening with the slope as time goes on? What does this mean about sea level rise in this area?
A: The slope looks like it stays the same over time. This means the sea level in this area is rising, but it is rising at the same rate as time goes on.
Q: Can you think of a way to more accurately describe the way the slope changes over time?
A: The most accurate way of determining if slope is changing over time is to determine the slope for smaller increments of time. For example, one could determine the slope for every five year increment and compare the change from many different five year periods.
Q: What information can you gain about the mean sea level in these areas just by looking at the graphs?
A: I can tell that the sea level varies from month to month because the lines on the graph go up and down and have an overall oscillating shape. I can tell that data was not collected in Key West from about 1935-1939. It looks like the slope on the Boston, MA plot has increased a lot from about 2000-present.
Q: Do you think the sea level is rising in these areas? What do you think the effects of sea level rise will be in these areas?
A: Yes, sea level is rising according to the tide gauge data that has been recorded for about 100 years. Sea level rise will eventually inundate the land, forcing people and animals to find new homes, and will likely destroy plant life in the coastal regions.
Q: Where do you think sea level rise is more of a threat, Florida or Massachusetts?
A: Sea level rise is accelerating in Massachusetts meaning that effects are likely to be seen sooner than in Florida. Florida is a very low-lying state, so if sea level rises it will cover more land than in Massachusetts. Florida also has a lot of coastal land, which exposes it more to sea level rise and a very high concentration of people living on the coast.
In the video below, one of my students reflects on what he understood from the lab and what was still unclear to him.