Tidal Anomalies

The simple six-hour tidal curve is only a model. Local geography can create tidal anomalies such as double high waters, prolonged tidal stands, rapid rises after a slow start, tidal bores, and unusual stream reversals. The Solent is the classic UK example of a double high water and stand around high water, caused by the interaction of tidal waves moving through the Channel and around the Isle of Wight.

An anomaly matters because it changes the assumptions behind depth, clearance, harbour entry, and tidal gate calculations. A long stand may give a useful entry window; a rapid fall after the stand may close it quickly. A secondary port note or almanac warning can be more important than a neat interpolated answer from a generic curve.

When planning in an area known for anomalies, read the port notes, pilot book, and local tide curve carefully. Do not assume that every port rises and falls smoothly at one-sixth, two-sixths, three-sixths, two-sixths, one-sixth through the six hours.