The word "tides" is used to define the rise and fall in sea level resulting from the gravitational attraction of the moon and the sun. The result of this pull is a bulge in the ocean water almost in line with the position of the moon; one bulge toward the moon and one on the opposite side of the earth, away from the moon. When we observe the tides what we are actually seeing is the result of the earth rotating under this bulge.

Flooded coasts, such as this one in Florida, are becoming increasingly common.
New regional sea level scenarios help communities prepare for risks
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The most familiar evidence of the tides is the observed recurrence of high and low water on the coastline. These tides usually, but not always, reach a high and low level typically about six hours apart. The shape of the coastline, the local depth of the water, and the ocean floor topography also significantly impact the height and the timing of the tides.

According to a NOAA analysis, nuisance flood events in nearby Seattle have increased from roughly once every 1-3 years around 1950 to once every 6-12 months today.
U.S. ties record for number of high tide flooding days in 2018


The resources included in this collection support teachers who are instructing students about the causes of tides, but also it includes resources about the impacts of tides on coastal ecosystems and tides as an energy source. Some of the websites allow the teacher and student to view and use real time, historic, and predicted data for a large number of tide stations along the coast and in the Great Lakes. Lessons are included that will provide ideas for ways to use this data with students. Changing tides have significant impacts to the ecosystems along the coast. We have included resources that will help teach about the impacts of tides on some of these ecosystems.