InTeGrate Modules and Courses >Coastal Processes, Hazards and Society > Student Materials > Sea Level Change Over Different Time Periods > Daily to Centuries-Long Sea Level Change > Periodic Sea Level Change
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These materials are part of a collection of classroom-tested modules and courses developed by InTeGrate. The materials engage students in understanding the earth system as it intertwines with key societal issues. The collection is freely available and ready to be adapted by undergraduate educators across a range of courses including: general education or majors courses in Earth-focused disciplines such as geoscience or environmental science, social science, engineering, and other sciences, as well as courses for interdisciplinary programs.
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These student materials complement the Coastal Processes, Hazards and Society Instructor Materials. If you would like your students to have access to the student materials, we suggest you either point them at the Student Version which omits the framing pages with information designed for faculty (and this box). Or you can download these pages in several formats that you can include in your course website or local Learning Managment System. Learn more about using, modifying, and sharing InTeGrate teaching materials.
Initial Publication Date: December 7, 2016

Periodic Sea Level Change

Short-term (~12-48 hours typical) variations are due to tides, strong currents, wind waves, storms, etc. As the Earth rotates, its water and atmosphere are influenced by gravitational pull of both the Earth, neighboring planets, and the sun. Thus, water is often pulled outward away from the surface creating bulges and valleys on the surface of water bodies. These bulges and valleys move around the planet and are influenced by topographic and bathymetric highs and lows, and geographic barriers that combined to produce different tidal ranges globally. Meteorological fluctuations (atmospheric pressure change, wind and storm waves, evaporation/precipitation impacts, etc.) can influence periodic sea-levels that are out-of-step with the normal tidal behavior. Tides are not generally the subject of this discussion, but it is important to understand them (see the example in Figure 4.4 below).

Activate Your Learning

Can you read and interpret the hydrograph? Try it now!

An example of a tide gauge "hydrograph" record from San Francisco, CA is shown above. The record shows three days (January 11 through January 14, 2014) of water levels taken at 1‐minute increments. These measurements are shown in red. Height in meters from Mean Low‐Low Water (MLLW) is shown on the vertical axis of the hydrograph, and time is on the horizontal axis. Click the image to enlarge the graph in a new window so you can see the details.

  • Note the highly variable "squiggly" interval that initiated in the afternoon on January, 12 and extended into the morning of the 13th relative to the "smoother" record before and after.

Question 1 - Essay

So based on the above hydrograph, what is the range of daily water level change for this site?

Question 2 - Essay

Given what you know, what might account for the high-frequency variation in water levels here for that short interval of time?

If you need a hint, look at the weather records for San Francisco for this period to see if there is a correlation that might explain this pattern. For a look at weather records in the region check out: http://www.wunderground.com/history/airport/KSFO/2014/1/18/WeeklyHistory... (link is external) The blue line in this case is the "predicted" sea-level for this site based on historic observations. Actual observations (red line) are lower for the duration than what was predicted. The purple line here shows the "residual" values which is calculated by the subtracting the actual readings from what was predicted.

From this graph, residuals show that water levels were lower than historical averages at this site because the residual values are all below zero (negative values).

Question 3 - Essay

From this graph, residuals show that water levels were lower than historical averages at this site because the residual values are all below zero (negative values).

Does the event of the 12th and 13th help explain why water levels were lower than average for the duration of the observation? Or is another factor at play that is yet to be accounted for?

Feel free to visit the website where this data was taken (http://tidesandcurrents.noaa.gov/tsunami/# (link is external) (link is external) and explore other nearby sites to see if they show the same pattern for the same interval of time. For instance - does Monterey, California show similar patterns?

These materials are part of a collection of classroom-tested modules and courses developed by InTeGrate. The materials engage students in understanding the earth system as it intertwines with key societal issues. The collection is freely available and ready to be adapted by undergraduate educators across a range of courses including: general education or majors courses in Earth-focused disciplines such as geoscience or environmental science, social science, engineering, and other sciences, as well as courses for interdisciplinary programs.
Explore the Collection »