Reading path: Coastal field methods →
Choose a reference that matches the site
Before setting a survey window, identify the shoreline feature you need to observe and the water-level station that best represents it. Record the station name and ID, the date, and the time zone used. A clock time without a time zone can shift a comparison by hours; an unfamiliar station may represent a different part of the coast. NOAA’s CO-OPS API provides station observations and tide predictions, with date range, station, product, and time-zone options. [1]
Read the prediction as a forecast of tide timing
Tides are long-period waves whose regular rise and fall reflect gravitational forces from the Moon and Sun. A high or low tide marks the arrival of a crest or trough at a location; the difference between them is the tidal range. [2] Use a prediction to estimate when water level may be changing and to select a useful observation window. It does not describe wave run-up, surf, or whether a route along the shore will remain accessible. Treat it as one planning input, not a site safety assessment.
Make the window operational
Build a short worksheet with: site identifier, station identifier, prediction product, date, time zone, predicted tide phase or event, planned start and end, and the field observation time. Add a note for the route’s exposed sections and a planned end time that leaves room to leave the observation area before the conditions you are monitoring become unsuitable. If the route depends on a narrow strip of exposed shore, compare the forecast window with the actual waterline when you arrive. Record what you see instead of silently adjusting the original plan.
Separate forecast from observation
When possible, compare the prediction with observed water level from the same station and time basis. The API distinguishes observations from predictions, and water-level observations require a datum; the datum is the reference surface used for reported heights. [1] Keep those fields visible in your notes so values from different products are not mistaken for direct equivalents. A mismatch may matter for timing, but it does not by itself explain why the water differs. Waves, local exposure, and the station’s distance from the survey site can affect what is happening at the shoreline.
Close the loop in the field
At the site, note the waterline, whether the planned viewing area is exposed, and whether the observation could be completed as intended. If conditions prevent it, record the visit as incomplete and state why; do not treat a missing observation as evidence that an organism was absent. On later visits, use the same station and time conventions where practical. This makes tide context useful for comparing surveys while preserving the distinction between a predicted tide and the shore conditions actually encountered.
Sources & further reading
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