Tides in the Chesapeake Bay

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Updated on Nov 13, 2012

Abstract

I chose to study tides as my project during the summer of 2000 while I was at the Maryland Summer Science Center Horsehead Wetlands Program. One of the teachers there introduced the subject of tides to me and I found it very interesting. I have attended this camp for three years now and have learned that the marsh floods once a month, due to high tides. I had never gotten to experience this before and I thought it would interesting to see. The last day we came to the marsh it happened. One day we came to a marsh where there was practically dry land and the next day the water flooded up to our knees in the same marsh! This made me sure that tides would be my project.

This research project concerns two factors that affect tidal level. These factors are moon phase and wind direction; they will be tested to see if they have any affect upon the high tide mark in the Chesapeake Bay. Tides are the daily rise and fall of the oceans, bays, streams, rivers, etc. The usual frequency of tides is two high tides and two low tides daily. The lowest level of water is defined, as the "low tide water mark" while the highest water level is the "high tide water mark".

This project will have two problems. The problems will be: "Is the high tidal level of the Chesapeake Bay affected by moon phases?" and "Is the high tidal level of the Chesapeake Bay affected by of wind direction?" Both problems will be researched by going onto an Internet site that records oceanographic and wind data such as tidal level and wind direction. Using a calendar that is marked with the full and new moons, the moon phases can be identified.

All of my data (date, moon phase, wind direction, and tidal level) will be entered into a computer on a spreadsheet on Microsoft Excel 2000. Then graphs will be drawn up on the same program. The graphs will compare moon phases with tides and wind direction and tides.

In conclusion, this research project shows that moon phases did not affect the high tide mark in the Chesapeake Bay while the wind direction did. The hypotheses were: "I predict that the tidal level will be affected by moon phases," and "I predict that the tidal level will be affected by wind direction". The first hypothesis was proved wrong yet the second one was right. This was an unexpected turnout. The background information had said the moon phases had the predominant affect on the high tide but it did not. In the Chesapeake Bay, the wind direction was the predominant factor. I could use my data to do a more specific project on moon phases and tides.

Problem

  1. Is the tidal level of the Chesapeake Bay affected by moon phases?
  2. Is the tidal level of the Chesapeake Bay affected by wind direction?

Background Information

What is a tide?

A tide is the daily rise and fall of the oceans. The lowest level of water is defined, as the "low tide water mark" while the highest water level is the "high tide water mark". The usual frequency of tides is two high tides and two low tides daily. Sometimes there is only one of either. This is because of the specific shape of the land, and the water gets trapped within an enclosed area of land.

What causes tides?

Tides are caused by the gravitational pull of the sun and moon and by the rotation of the earth on its axis. As the earth spins, each part of the water is under the moon once about every 24 hours. The water bulging towards the moon makes the high tide. The centrifugal force causes another high tide on the opposite side of the earth. The centrifugal force is the force that pulls a thing outward from the center when it is spinning. This force pulls the water away from the earth to form a bulge while it is spinning.

What affects tides?

Tides are affected by the sun’s gravitational pull. The moon’s gravity also affects them. Although the sun is 27 million times larger than the moon, it is also 400 times further away. So the tidal force caused by the Sun is 50% less than the tidal force of the moon. Also moon phases affect tides. During the full and new moon, also referred to as spring tides, the tides are 20% larger and during first and third quarter moons, also referred to as neap tides, the tides are 20% smaller.

What are spring and neap tides?

During spring tides the tides are 20% bigger. Spring tides are when the sun, moon, and earth are lined up in a linear fashion. This causes higher high tides and lower low tides. This is because the sun and moon’s gravitational pulls are working to pull the water out higher in a higher high tide. Thus forming a lower low tide. Spring tides occur on new and full moons. During neap tides the tides are 20% smaller. Neap tides are when the sun, moon, and earth form a right angle. This causes higher low tides and lower high tides. Neap tides occur during the first and third quarter moon.

Hypothesis

  1. I predict that the tidal level in the Chesapeake Bay will be affected by moon phases.
  2. I predict that the tidal level in the Chesapeake Bay will be affected by wind direction.

Materials

  • Internet (http://co-ops.nos.noaa.gov/)
  • Computer
  • Microsoft Excel 2000

Procedure

Internet

  1. Get onto the Internet and type http://co-ops.nos.noaa.gov/
  2. Click on Water Level Observations
  3. Go under Verified/Historical Water Level Data and click on U.S and Global Coastal Stations
  4. Select Station: 8573364 Tolchester Beach, Chesapeake Bay, MD
  5. Choose Time Interval: W3-Highs/Lows
  6. Pick Datum: MLLW
  7. Click Data Units: Meters
  8. Type Begin Date: 20000701 & End Date 20000731
  9. Select Output Format: yyyy/mm/dd hh:mm
  10. Click Time Zone UTC
  11. Click on View Data button
  12. Repeat steps above replacing Step 8 with 20000801 & 20000831 for August, 20000901 & 20000930 for September, and 20001001 & 20001031 for October

Entering Data

  1. Turn on computer and get into Microsoft Excel 2000
  2. Create a spreadsheet titled "Tidal Level Data Table"
  3. Title the first column "Date", the second column "Moon Phase", the third column "Wind Direction", and the fourth column "High TideLevel"
  4. Enter all the data that was collected from the internet, into the spreadsheet
  5. Then create a Scatter Plot graph comparing the moon phases and the high tide level
  6. Make another Scatter Plot graph but this time compare the wind direction to the high tide level
  7. Analyze data for patterns and trends
  8. Write a conclusion

Data

Data was collected from a NOAA website (http://co-ops.nos.noaa.gov/) for the period from July 1, 2000 through Oct. 31, 2000. The data was put on an Excel Spreadsheet. 2 scatterplots were done:

  • Relating moon phase and mean high tide level
  • Relating mean wind direction for that period and mean high tide level. I coded the moon phase and wind directions as numbers so that I could graph them. The code keys are under each graph. See http://www.qacps.k12.md.us/cms/sci/Tidehmm.HTM

Conclusion

Wind Direction

Tidal level in the Chesapeake Bay is affected by the wind direction. When the wind was blowing toward the south, (180º) the water was being pushed out of the Bay and it created lower high tides. This shows that my second hypothesis was right! I think that these results are significant enough to be used by scientists. The results make sense because, when the tidal level is lower, the wind direction is near 180º, and when it is higher, the wind direction is near 0. Some factors that could affect the tidal level, like the sun’s gravitational pull, the wind speed, and wind duration could have changed the results. I could use this data in further experiments to figure out what else affects the tidal level of the Chesapeake Bay.

Moon Phases

Tidal level in the Chesapeake Bay is not affected by moon phases. During the full and new moons, the high tidal level should be the highest. During 1st and 3rd quarter moons, the high tides should be the lowest. Instead the high tide levels seem to show no pattern with the moon phases. During 1st and 3rd quarter moons the high tides are just as high as when there are new and full moons. Also the tides during the 1st and 3rd quarter moons should be lower than average and they are not. This shows that my hypothesis about moon phases was incorrect. In my background reading, it was proved by other scientists that moon phases do affect tidal level. When I did this project, I came up with something else. The Chesapeake Bay results were different than the background reading research because the research was probably done on open bodies of water such as oceans. The Bay has one main mouth where all the water must go in and out during the tides. Oceans typically have less land surrounding them and the water is not limited about where it comes and goes. I could use this data in further experiments on tides.

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