A tide gauge is a device for measuring the change in

sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardised g ...

relative to a

vertical datum In geodesy, surveying, hydrography and navigation, vertical datum or altimetric datum, is a reference coordinate surface used for vertical positions, such as the elevations of Earth-bound features (terrain, bathymetry, water level, and built stru ...

. It its also known as mareograph, marigraph, sea-level recorder and limnimeter. When applied to

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...

continental

water bodies A body of water or waterbody (often spelled water body) is any significant accumulation of water on the surface of Earth or another planet. The term most often refers to oceans, seas, and lakes, but it includes smaller pools of water such as p ...

, the instrument may also be called a limnimeter.

Operation

Sensors continuously record the height of the

water level Water level, also known as gauge height or stage, is the elevation of the free surface of a sea, stream, lake or reservoir relative to a specified vertical datum.ISO 772: 1996. Hydrometric determinations – Vocabulary and symbols. See also * ...

with respect to a height reference surface close to the

geoid The geoid () is the shape that the ocean surface would take under the influence of the gravity of Earth, including gravitational attraction and Earth's rotation, if other influences such as winds and tides were absent. This surface is extended ...

. Water enters the device by the bottom pipe (far end of the tube, see picture), and electronic sensors measure its height and send the data to a tiny computer. Historical data are available for about 1,450 stations worldwide, of which about 950 have provided updates to the global data center since January 2010. At some places records cover centuries, for example in

Amsterdam Amsterdam ( , , , lit. ''The Dam on the River Amstel'') is the Capital of the Netherlands, capital and Municipalities of the Netherlands, most populous city of the Netherlands, with The Hague being the seat of government. It has a population ...

where data dating back to 1700 is available. When it comes to estimating the greater ocean picture, new modern tide gauges can often be improved upon by using satellite data. Tide gauges are used to measure

tides Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables can ...

and quantify the size of

tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explo ...

s. The measurements make it possible to derive the mean

. Using this method, sea level slopes up to several 0.1 m/1000 km and more have been detected. A tsunami can be detected when the sea level begins to rise, although warnings from

seismic activity An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...

can be more useful.

History

Sea-level measurements were made using simple measuring poles or "tide staffs" until around 1830, when self-recording gauges with mechanical floats and stilling wells were introduced. Tidal poles and float gauges were the primary means of sea-level measurement for over 150 years and continue to operate at some locations today. While still part of modern-day tide gauge instrumentation, these technologies have since been superseded by pressure gauges (similar to

depth gauge A depth gauge is an instrument for measuring depth below a reference surface. They include depth gauges for underwater diving and similar applications, and engineering instruments used to measure the depth of holes and indentations from a refer ...

s), acoustic/ultrasonic gauges, and radar gauges. The following types of tide gauges have been used historically: * Kelvin type tide gauge * Fuess type tide gauge * GSI type tide gauge * High accuracy automatic tide gauge * High resolution automatic tide gauge

Common applications

Tide gauges have a practical application in the shipping and fishing industries where low or high tide levels can hinder or prohibit access to shallow bays or locations with bridges. An example is the

Cascais tide gauge The Cascais tide gauge ( pt, Marégrafo de Cascais) was the first tide gauge (also known as a mareograph or marigraph, as well as a sea-level recorder) installed in Portugal and dates back to 1882. It is situated in Cascais Municipality, Lisbon Dis ...

in Portugal, which was originally installed because of the sand bar in the River

Tagus The Tagus ( ; es, Tajo ; pt, Tejo ; see #Name, below) is the longest river in the Iberian Peninsula. The river rises in the Montes Universales near Teruel, in mid-eastern Spain, flows , generally west with two main south-westward sections ...

that causes difficulties for shipping entering

Lisbon Lisbon (; pt, Lisboa ) is the capital and largest city of Portugal, with an estimated population of 544,851 within its administrative limits in an area of 100.05 km2. Grande Lisboa, Lisbon's urban area extends beyond the city's administr ...

port. Because of similar problems many industries have installed private tide gauges in ports around the world, and also rely on government agencies (such as

NOAA The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditio ...

). Data collected from tide gauges is also of interest to scientists measuring global weather patterns, the mean sea water level, and trends - notably those potentially associated with global warming.

Modern gauges

In recent years new technologies have developed allowing for real-time, remote tide information to be published online via a solar powered wireless connection to a tide sensor. Acoustic/ultrasonic sensors have already been deployed to great effect and the data is regularly broadcast via

Twitter Twitter is an online social media and social networking service owned and operated by American company Twitter, Inc., on which users post and interact with 280-character-long messages known as "tweets". Registered users can post, like, and ...

and also displayed online.

References

External links

Historical Examples
Brown University
Mean Sea Level ExplanationNOAA Tide Data
{{DEFAULTSORT:Tide Gauge *