Shop Windows to the Universe

Our Glaciers: Then and Now activity kit helps you see the changes taking place in glaciers around the world. See all our activity kits and classroom activities.
An extreme low tide in winter. Image taken of the Maryland coastline on January 1, 1998. In this image, you can see small pools of water left when the tide went out and footprints of someone who walked in the sand during low tide. Both of these features will be covered up when the tide begins to increase again and the water level rises.
Click on image for full size
Courtesy of NOAA

Tidewater

Have you ever walked along a beach at low tide? Everyone likes to look for uncovered sea shells or the small creatures in leftover puddles of water during low tide. One thing is for sure, low tide can look really different than high tide!

Tidewater is water that is affected by the ebb and flow of tides. A tidewater region is a region that is affected by tides. When you hear someone say they live on the coast of an ocean or sea, they live in a tidewater region. Rivers that flow into the ocean, estuaries, and salt marshes are also affected by the tides and so are important parts of a tidewater region.

The ebb and flow of tides has a large effect on life in a tidewater region. People need to know how far out to put their boat so that the boat doesn't get stuck (and possibly damaged!) in the bottom of the empty sea during low tide. It also affects the time when you may want to go to the beach and where and when you (or a fishing company) would catch the most fish. Tides affect the amount of nutrients in the water, and other water characteristics like salinity and temperature which greatly affect ocean creatures that live in coastal waters, estuaries, rivers near the sea, or salty marshes. Tides are so important that some creatures base their feeding or reproductive schedules mainly on the tidal cycle.

Gravitational forces of the Moon and Sun on the Earth cause tides. As the tide flows in, water level rises and rises. When the water reaches its highest level, it is considered high tide. After the point of high tide, the waters ebb away. When the water reaches its lowest point, it is considered low tide. The high tide-low tide cycle can occur once a day in some places, twice a day in others. The water level difference between high and low tide varies from a few centimeters to 13 meters depending on the location. Tide tables are put together for coastal areas around the world that tell us when high and low tide will occur for a given place on a given day.

Last modified June 1, 2010 by Lisa Gardiner.

Shop Windows to the Universe Science Store!

The Spring 2010 issue of The Earth Scientist, focuses on the ocean, including articles on polar research, coral reefs, ocean acidification, and climate. Includes a gorgeous full color poster!

Windows to the Universe Community

News

Opportunities

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Rivers

Rivers are very important to Earth because they are major forces that shape the landscape. Also, they provide transportation and water for drinking, washing and farming. Rivers can flow on land or underground...more

Tidal Forces

The force of gravity caused by an object gets weaker as you move farther away from that object. In this picture, the Earth is pulling on the Moon, and the Moon is pulling on the Earth. The Moon pulls more...more

Sea Level

Measuring sea level, the height of the ocean surface, allows scientists to calculate whether sea level is changing over time and how much sea level rise is happening now because of global warming. But...more

Aquifer

An aquifer is the name for a layer of rock which is capable of holding a large amount of water. Some layers are better at holding water than others, for example a layer of sandstone can hold a good deal...more

Carbonates

Carbonate is a name for rocks and minerals which contain a molecule made of both carbon and oxygen known as CO32-. (CO32- is also known as the molecule carbonate). Limestone is an example of a calcium...more

Deep Water and the CO2 cycle

The deep ocean waters are under pressure and are much colder than layers of the ocean which are closer to the surface. Dissolved carbon dioxide seems to be absent from the deep ocean water and as a result...more

Evaporation

One process which transfers water from the ground back to the atmosphere is evaporation. Evaporation is when water passes from a liquid phase to a gas phase. Rates of evaporation of water depend on things...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF