Tidal Stream

The horizontal movement of water caused by the rise and fall of the tide.

A tidal stream refers to the flow of water generated by the gravitational pull of the moon and the sun, which causes the sea level to rise and fall in a cyclical manner. This movement of water is distinct from ocean currents, which are driven by factors such as wind, temperature, and salinity differences. Tidal streams are predictable and follow a regular pattern based on the lunar cycle, making them a crucial consideration for mariners navigating coastal waters. The speed and direction of a tidal stream can vary significantly depending on geographic location, the shape of the coastline, and the depth of the water. In narrow channels, estuaries, or around headlands, tidal streams can become particularly strong, sometimes reaching several knots, which can either aid or hinder a vessel’s progress. Understanding tidal streams is essential for safe navigation, as they can affect a boat’s course, speed, and fuel consumption. Charts, tide tables and Tidal Stream Atlases are used to predict the timing and strength of tidal streams, allowing mariners to plan their journeys accordingly. In some areas, tidal streams can also create hazardous conditions, such as whirlpools or overfalls, where the water’s movement becomes turbulent due to underwater features or constrictions in the coastline.