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How to Monitor Tides

Tides are mostly caused by the gravitational pull of the moon on the ocean. This pull causes bulges and troughs on the ocean surface. When these bulges reach the shore, we experience high tide. When the troughs reach the shore, we experience low tide. Tides follow the lunar day, which is 24 hours and 50 minutes, the time it takes for the moon to revolve completely around the earth. Thus, in most areas, there are two high and two low tides each 24 hours and 50 minutes, or a high tide every 12 hours and 25 minutes. You can monitor tides online at the National Oceanographic and Atmospheric Administration website, or monitor them yourself if you have access to a tide gauge on a pier.

Things You'll Need

Tide table book

Instructions

Monitoring Tides Online
- 1
  Go to http://tidesonline.nos.noaa.gov/ with your Internet browser. This is the Tides Online website. On the left-hand side of the screen you'll see several options to select which station you are interested in. You can choose by high water condition, state maps or regional list. Click on "state maps."
- 2
  Choose a state from the United States map. The map will change to a map of the selected state. Each monitoring station is indicated by name and a red dot. Select the monitoring station closest to the area you are interested in.
- 3
  Read the graph displayed. The top graph is water levels. The horizontal x-axis is date and time, and the vertical y-axis is water height above mean lower low water, MLLW. MLLW is the average of the lowest water level recorded at the station over time. The red line indicates recorded tides. The blue line is the predicted levels, which extend 24 hours into the future. Note the tide levels and times you are interested in. Also note the slight discrepancy between predicted and actual water levels.
Monitoring Tides Manually
- 4
  Find a pier that has the water levels marked on one of the pilings. This is a tidal gauge. It is easiest to read these gauges in areas of low wave action.
- 5
  Consult a tide table to determine the time of high and low tide at your location each day.
- 6
  Record the water level at high and low tide. If there are waves, record the water level at the crest of several waves and at the trough of several waves and take an average. For example, record five crest heights, add them together and divide by five. Record five trough heights, add them together and divide by five. Then take the average high + the average low and divide by two. This will give you the average tidal height. Chart on a graph with time on the horizontal x-axis and height on the vertical y-axis. In time, you will be able to extrapolate forward in time, and estimate the tides in that area. Keep in mind that these will just be estimations, and should not be used for navigation, as other factors, such as storms at sea, can change the tidal conditions quickly.

Nature