How Do You Measure Ocean Tides?
You may know that oceans are affected by tides. But HOW are tides measured? You would be tempted to just measure the tidal change within calm inlets and extrapolate the information to other areas.
Unfortunately, the tide doesn’t affect beaches the same way at all. Consider the Bay of Fundy, renowned for having the most extreme tides in the world. One spot typically experiences a 20 foot tide, while another experiences a 50 foot tide on the same day. Gadzooks!
Where are the tides measured?
So you need to go out and measure everywhere. But now you have a big challenge. Most coastlines have waves. How do you separate out the effect of the waves from the rise of the tide? Especially when some places have humongous waves. Check out this video of Garret McNamara riding a 90 foot wave.
So how do you measure a tide?
Especially how did they do it before electronics, satellites, lasers, radar, electric motors or submarines?
Please allow me to present, The Stilling Well.
To understand a stilling well, start by imagining a long measuring stick firmly planted in the ocean well beyond the line of breakers. So far so good, but some poor soul is going to have to try to read numbers off of that thing while hanging over the side of a boat.
Improve it by replacing that measuring stick with a long tube about 10 inches wide. Plant that pipe firmly into the ocean floor and drill a large hole through it just above the bottom end. Water can pass in and out of the tube completely unrestricted.
Waves churn water below the surface to the same depth as they extend above the surface. So a six foot tall wave affects the water six feet below the wave’s low point. But below that point the water is not much affected by the waters. So if the hole in the pipe is deep enough … Eureka! No wave action.
Add a string from the ocean floor to a float and you have a measuring device. The first self-recording float gauge was developed in 1842.
This self-recording float gauge installed in a stilling well is a wonderfully low tech and common solution. More modern tidal gauges have started to replace it where extreme accuracy is needed, but this simple, reliable device is still widely used over the world today.
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