What are tide tables? | How it works

Time and tide wait for no one, not even a little boy who rushes to finish his sandcastle before it is swept away. With astonishing regularity, Earth’s oceans rise and fall daily, due to the gravitational pull of the moon and sun on the Earth’s surface. These variations in water level are called tidesand knowing when they will happen is essential for a variety of people, including the budding architect on the beach.

Government agencies around the world measure the tides daily to predict when the two highest and lowest tides in an area will occur and how high they will be. This compilation of data is called a tide chart. Tides have little effect on the high seas and in lakes, so tables are generated primarily for coastal areas, coves, bays and estuaries.

Unsurprisingly, boats rely heavily on tidal information. Traveling through shallow harbors and narrow intra-coastal waterways or under bridges is risky business if you don’t know what’s going on with the tides. Depending on the area, the difference between high and low tides, or the marlingcan be over 49 feet (15 meters) [source: NOAA: Tides and Water Levels]. If you’re a starship captain steering your ship under a low bridge, underestimating the range could be devastating.

Anglers often tap into tidal information to improve their catches as certain species of fish may congregate during periods of high or low water. Also, strong tidal currents can congregate fish in an area, and if anglers know when that current is coming, they’ll hit the jackpot.

Tide tables are also useful for planning coastal construction projects, as well as coastal rehabilitation and disaster cleanup work. Many people also use the tables for recreational purposes, such as surfers looking to catch the ultimate wave.

On the next page, learn how a division of NOAA prepares tide tables and why their predictions aren’t always 100% accurate.

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