Two visits to the same shore can reveal different high-water marks even within one tidal cycle. The idea that every high tide reaches the same height is a tidy mental picture, but coastlines do not all follow that picture.
Start with the pattern names
NOAA’s guide to tidal cycles distinguishes a diurnal pattern, with one high and one low water per lunar day, from a semidiurnal pattern with two of each. In a mixed semidiurnal pattern, the successive highs or lows have unequal heights. The names describe patterns rather than a promise about your next visit.
Draw a pair of unequal peaks
On paper, sketch two peaks with different heights and place a low point between them. Keep the vertical axis labelled “illustrative water level” rather than adding invented local measurements. The drawing helps separate the number of highs from their height.
Then compare it with two peaks of similar height. Both sketches have two highs; that shared count does not make their shape identical. A visual distinction can be easier to remember than a list of unfamiliar terms.
Return to local information for a real outing
Use the appropriate current local tide information and site guidance when planning access. Neither this sketch nor a remembered high-water line establishes when a path will remain available. Weather and local conditions also matter.
Read how the shoreline changes between high and low tide as an observation companion. A useful shore note includes the time and location, then separates what you saw from the wider tidal pattern you are trying to understand.