What does the coast do in two days?
Explore real hourly water-level measurements. Look for patterns, then test how much the sampling interval changes what you notice.
What water-level patterns appear over two days, and what might less frequent sampling hide?
A tide gauge measures water level compared with a fixed reference level called a datum. This record uses MLLW: mean lower low water, a reference based on long-term tide measurements. Zero is not the seafloor. Negative values are possible. Tides affect water level, but weather and other conditions can also affect it.
Review the related lesson →Science words you will use
A hypothesis is a possible explanation. A prediction is what you expect to observe. The independent variable is what you change or compare; the dependent variable is what you measure. Controlled variables stay the same in a fair test. Qualitative observations describe what you notice; quantitative observations use numbers and units.
Accuracy means closeness to a trusted value. Precision describes how closely repeated readings agree. Repeating a result does not prove it is accurate. A pattern between two quantities does not, by itself, show that one caused the other.
Read a real coastal record
Use 48 verified hourly observations from NOAA station 9414290, San Francisco, for January 1–2, 2020. Times are UTC, not Calgary or San Francisco local time. These are measured water levels, not tide predictions. Select a view below; the original record stays unchanged.
Station 9414290 · San Francisco · January 1–2, 2020 · UTC · metres relative to MLLW
Open original NOAA response · Download the source record
Hourly points may miss peaks between readings. The reference level is not the seafloor. Changing the sampling view does not change the original record.
Materials & safety
- NOAA hourly water-level record
- Digital notebook
This investigation uses a recorded dataset. It does not require visiting the shore. Never use this classroom record for boating or coastal safety decisions.
Suggested procedure — adapt and record changes
- Write a question and a prediction before loading the record. This is an observation study: you do not control the tides.
- Load all 48 hourly observations. Check the station, dates, time zone, units and reference level.
- Graph water level against hours since January 1, 2020 at 00:00 UTC. Identify the highest and lowest sampled values and when they occurred.
- Compare every-hour, every-third-hour and every-sixth-hour views. These are subsets of the same record, not new measurements. What details disappear?
- Check your claim against the complete hourly record. An hourly sample may miss the exact highest or lowest level between readings.
- Explain what these two days can and cannot show. You cannot use them alone to prove a long-term sea-level trend or identify the cause of every change.
Plan your investigation
Use your own words. You can return and change your ideas as you collect evidence.
Your data and graph
Explain, question and reflect
A new question to explore
Design a longer observation study. What extra dates, stations or weather records would help you check an explanation?
Your lab report
Download a report with your notes, measurements, calculations and graph. Open it in a browser and choose Print → Save as PDF. Submit that PDF in Google Classroom using your teacher’s instructions. This website does not submit your work.
A backup is a JSON file for restoring this notebook. It is different from your finished report. Keep your own copy before clearing browser data or changing devices.