NOAA Shoreline Website

Glossary

A

accretion

The gradual and imperceptible accumulation of land by natural causes, as out of the sea or a river. This may be the result from a deposit of alluvion upon the shore, or by a recession of the water from the shore. Accretion is the act, while alluvion is the deposit itself. (Shalowitz 1964)

accuracy

Degree of conformity with a standard. Accuracy relates to the quality of a result and is distinguished from precision which relates to the quality of the operation by which the result is obtained. (Ellis 1978)

apparent shoreline

Line drawn on a map or chart in lieu of a mean high water line (MHWL) or the mean water level line (MWLL) in areas where either may be obscured by marsh, mangrove, cypress, or other type of marine vegetation. This line represents the intersection of the appropriate datum on the outer limits of vegetation and appears to the navigator as the shoreline. (Ellis 1978)

avulsion

The loss of lands bordering on the seashore by sudden or violent action of the elements, perceptible while in progress; a sudden and rapid change in the course and channel of a boundary river. Neither of these changes works a change in the riparian boundary. (Shalowitz 1964)

B

backshore

That part of the beach that is usually dry, being reached only by the highest tides, and by extension, a narrow strip of relatively flat coast bordering the sea. (Ellis 1978)

bank

Edge of a cut or fill; the margin of the watercourse; an elevation of the seafloor located on a continental shelf or an island shelf and over which the depth of water is relatively shallow but sufficient for safe surface navigation (reefs or shoals, dangerous to surface navigation may arise above the general depths of a bank). (Ellis 1978)

base line

The line from which maritime zones are measured. The coast line. A combination of the low-water line and closing lines across the mouths of inland water bodies. (Reed 2000)

bathymetry

Science of measuring water depths (usually in the ocean) in order to determine bottom topography. (Ellis 1978)

beach (or seabeach)

Zone of unconsolidated material that extends landward from the low water line to the place where there is marked changes in material or physiographic form, or to the line of permanent vegetation (usually the effective limit of storm waves). A beach includes foreshore and backshore. (Ellis 1978)

beach berm

Nearly horizontal portion of the beach or backshore formed by the deposit of materials by wave action. Some beaches have no berms, others have one or several. (Ellis 1978)

bench mark (BM)

A fixed physical object or mark used as reference for a vertical datum. A tidal bench mark is one near a tide station to which a tide staff and tidal datums are referred. A primary bench mark is the principal (or only) mark of a group of tidal bench marks to which the tide gauge measurements and tidal datums are referred. The standard tidal bench mark of the National Ocean Service is a brass, bronze, or aluminum alloy disk 3-½ inches in diameter containing the inscription NATIONAL OCEAN SERVICE together with other individual identifying information. A vertical geodetic bench mark identifies a surveyed point in the National Geodetic Vertical Network. Most geodetic bench mark disks contain the inscription VERTICAL CONTROL MARK NATIONAL GEODETIC SURVEY with other individual identifying information. Bench mark disks may also be horizontal control points and are so designated on their stampings. Bench mark disks of either type may, on occasion, serve simultaneously to reference both tidal and geodetic datums. Numerous bench marks of predecessor organizations to NOS, or parts of other organizations absorbed into NOS, still bear the inscriptions: U.S. COAST & GEODETIC SURVEY, NATIONAL OCEAN SURVEY, U.S. LAKE SURVEY, CORPS OF ENGINEERS, and U.S. ENGINEER OFFICE. (NOS CO-OPS 1 2000)

bench mark (tidal)

Bench mark set to reference a tide staff at a tidal station, the elevation of which is determined with relation to the local tide station. (Ellis 1978)

berm

Nearly horizontal portion of a beach or backshore having an abrupt fall and formed by wave deposition of material and marking the limit of ordinary high tides. (Ellis 1978)

berm crest

Seaward limit of a berm. (Ellis 1978)

bluff

A cliff or headland with an almost perpendicular face. (Hydrographic Dictionary 1990)

bottom lands

Land below navigable freshwater bodies. (Coastal States Organization 1997)

boundary survey

Survey made to establish or to reestablish a boundary line on the ground, or to obtain data for constructing a map or plat showing a boundary line. (Ellis 1978)

C

chart, nautical

A printed reproduction of a compilation of data derived from topographic and hydrographic surveys and miscellaneous information for use in marine navigation. The distinction between a survey and a chart is that the first is an original record of a given date, whereas the second is a compilation of many surveys of different dates. (Shalowitz 1964)

cliff

Land rising abruptly for a considerable distance above the water or surrounding land. (Hydrographic Dictionary 1990)

coast

General region of indefinite width that extends from the sea inland to the first major change in terrain features. (Ellis 1978)

coastal boundary

The mean high water line (MHWL) or mean higher high water line (MHHWL) when tidal lines are used as the coastal boundary. Also, lines used as boundaries inland of and measured from (or points thereon) the MHWL or MHHWL. (NOS CO-OPS 1 2000)

coastal zone (legal definition for coastal zone management)

The term coastal zone means the coastal waters (including the lands therein and thereunder) and the adjacent shorelands (including the waters therein and thereunder), strongly influenced by each and in proximity to the shorelines of the several coastal states, and includes islands, transitional and inter-tidal areas, salt marshes, wetlands, and beaches. The zone extends, in Great Lakes waters, to the international boundary between the Unites States and Canada and in other areas seaward to the outer limit of the United States territorial sea. The zone extends inland from the shorelines only to the extent necessary to control shorelands, the uses of which have a direct and significant impact on the coastal waters. Excluded from the coastal zone are lands the use of which is by law subject solely to the discretion of or which is held in trust by the Federal Government, its officers, or agents. (NOS CO-OPS 1 2000)

coast line

The term used in the Submerged Lands Act to describe the low-water line and closing lines across the mouths of inland water bodies. The same as “baseline” in the Convention. (Reed 2000)

coastline

The water/land interface. The shoreline. A more general term than “coast line.” (Reed 2000)

contiguous zones

A zone seaward of the territorial sea in which coastal states may assert jurisdiction short of complete sovereignty. Article 24 of the Convention on the Territorial Sea and the Contiguous Zone authorizes such a zone "to prevent infringement of its customs, fiscal, immigration or sanitary regulations in territory or territorial sea..."  Under the Convention the contiguous zone may extend no more than 12 miles from the coast line. (Reed 2000)

control station

Point on the ground whose position (horizontal or vertical) is used as a base for a dependent survey. (Ellis 1978)

coordinated universal time (UTC)

The time scale that is available from most broadcast time signals. It differs from International Atomic Time by an integral number of seconds. UTC is maintained within 1 second of UT1 by the introduction of 1second steps (leap seconds) when necessary, normally at the end of December. DUT1, an approximation of the difference UT1 minus UTC, is transmitted in code on broadcast time signals. (Hydrographic Dictionary 1990)

cotidal line

A line on a chart or map passing through places having the same cotidal hour. (Hicks 1984)

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D

datum (chart)

The datum to which soundings on a chart are referred. It is usually taken to correspond to a low-water elevation. Since 1989, chart datum has been implemented to mean lower low water for all marine waters of the United States, its territories, Commonwealth of Puerto Rico, and Trust Territory of the Pacific Islands. See datum and National Tidal Datum Convention of 1980. (NOS CO-OPS 1 2000)

datum (tidal)

A level of the sea defined by some phase of the tide, from which water depths and heights of tide are reckoned. (Hydrographic Dictionary 1990)

datum (vertical)

For marine applications, a base elevation used as a reference from which to reckon heights or depths. It is called a tidal datum when defined in terms of a certain phase of the tide. Tidal datums are local datums and should not be extended into areas which have differing hydrographic characteristics without substantiating measurements. In order that they may be recovered when needed, such datums are referenced to fixed points known as bench marks. (NOS CO-OPS 1 2000)

differential GPS

Differential GPS is implemented by placing a GPS monitor receiver at a precisely known location. Instead of computing a navigational fix, the monitor determines the range error to every GPS satellite it can track. These ranging errors are then transmitted to local users where they are applied as corrections before computing the navigation result. (Hydrographic Dictionary 1990)

diurnal

Having a period or cycle of approximately one tidal day. Thus, the tide is said to be diurnal when only one high water and one low water occur during a tidal day, and the tidal current is said to be diurnal when there is a single flood and a single ebb period of a reversing current in the tidal day. A rotary current is diurnal if it changes its direction through all points of the compass once each tidal day. A diurnal constituent is one which has a single period in the constituent day. The symbol for such a constituent is the subscript 1. (NOS CO-OPS 1 2000)

diurnal range (Great) (Gt)

The difference in height between mean higher high water and mean lower low water. The expression may also be used in its contracted form, diurnal range. (NOS CO-OPS 1 2000)

diurnal tide level

A tidal datum midway between mean higher high water and mean lower low water. (NOS CO-OPS 1 2000)

dry sand beach

Sandy area between the mean high tide line and the vegetation line. (Coastal States Organization 1997)

E

epoch

(1) Also known as phase lag. Angular retardation of the maximum of a constituent of the observed tide (or tidal current) behind the corresponding maximum of the same constituent of the theoretical equilibrium tide. It may also be defined as the phase difference between a tidal constituent and its equilibrium argument. As referred to the local equilibrium argument, its symbol is k. When referred to the corresponding Greenwich equilibrium argument, it is called the Greenwich epoch that has been modified to adjust to a particular time meridian for convenience in the prediction of tides is represented by g or by k'. The relations between these epochs may be expressed by the following formula:

G = k + pL

g = k' = G - aS / 15

in which L is the longitude of the place and S is the longitude of the time meridian, these being taken as positive for west longitude and negative for east longitude; p is the number of constituent periods in the constituent day and is equal to 0 for all long-period constituents, 1 for diurnal constituents, 2 for semidiurnal constituents, and so forth; and a is the hourly speed of the constituent, all angular measurements being expressed in degrees. (2) As used in tidal datum determination, it is 19-year cycle over which tidal height observations are meaned in order to establish the various datums. As there are periodic and apparent secular trends in sea level, a specific 19-year cycle (the National Tidal Datum Epoch) is selected so that all tidal datum determinations throughout the United States, its territories, Commonwealth of Puerto Rico, and Trust Territory of the Pacific Islands, will have a common reference. (NOS CO-OPS 1 2000)

erosion

Transportation of weathered (decomposed) rock material or soil by natural forces. (Ellis 1978)

estuary

An embayment of the coast in which fresh river water entering at its head mixes with the relatively saline ocean water. When tidal action is the dominant mixing agent it is usually termed a tidal estuary. Also, the lower reaches and mouth of a river emptying directly into the sea where tidal mixing takes place. The latter is sometimes called a river estuary. (NOS CO-OPS 1 2000)

extreme high water

The highest elevation reached by the sea as recorded by a tide gauge during a given period. The National Ocean Service routinely documents monthly and yearly extreme high waters for its control stations. (NOS CO-OPS 1 2000)

extreme low water

The lowest elevation reached by the sea as recorded by a tide gauge during a given period. The National Ocean Service routinely documents monthly and yearly extreme low water for its control stations. (NOS CO-OPS 1 2000)

F

first reduction

A method of determining high and low water heights, time intervals, and ranges from an arithmetic mean without adjustment to a long-term series through simultaneous observational comparisons. (NOS CO-OPS 1 2000)

foreshore

That part of shore which lies between high and low water mark at ordinary tide.(Hydrographic Dictionary 1990)

freshwaters

Waters that do not ebb and flow with the tide. The determinative factor is that the water body does not ebb and flow with the tide, not the salt content of the water. (Coastal States Organization 1997)

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G

gauge

See tide gauge. (Hicks 1984)

geodesy

Often used to include both the science which must depend upon determinations of the figure and size of the Earth from direct measurements made on its surface(triangulation, leveling, astronomic and gravity determinations), and t he art which utilizes the scientific determinations in a practical way and is usually termed geodetic surveying or geodetic engineering. (Ellis 1978)

global positioning system (GPS)

A satellite navigation system intended to provide highly accurate position and velocity information in three dimensions and precise time and time interval on a global basis continuously. (Hydrographic Dictionary 1990)

Greenwich Mean Time (GMT)

Mean solar time at the Greenwich meridian. (Hydrographic Dictionary 1990)

Gulf Coast Low Water Datum line (GCLWD)

A tidal datum. Used as chart datum from November 14, 1977, to November 27, 1980, for the coastal waters of the Gulf coast of the United States. GCLWD is defined as mean lower low water when the type of tide is mixed and mean low water (now mean lower low water) when the type of tide is diurnal. (NOS CO-OPS 1 2000)

H

half tide level

A tidal datum. The arithmetic mean of mean high water and mean low water. Same as mean tide level. (NOS CO-OPS 1 2000)

harmonic analysis

The mathematical process by which the observed tide or tidal current at any place is separated into basic harmonic constituents. (NOS CO-OPS 1 2000)

harmonic prediction

Method of predicting tides and tidal currents by combining the harmonic constituents into a single tide curve. The work is usually performed by electronic digital computer. (NOS CO-OPS 1 2000)

head of tide

The inland or upstream limit of water affected by the tide. For practical application in the tabulation for computation of tidal datums, head of tide is the inland or upstream point where the mean range becomes less than 0.2 foot. Tidal datums (except for mean water level) are not computed beyond. (NOS CO-OPS 1 2000)

higher high water (HHW)

The higher of the two high waters of a tidal day where the tide is of the semidiurnal or mixed type. The single high water occurring daily during periods when the tide is diurnal as considered to be higher high water. (Shalowitz 1964)

higher low water (HLW)

The higher of the two low waters of a tidal day where the tide is of the semidiurnal or mixed type. (Shalowitz 1964)

high tide

Same as high water. (NOS CO-OPS 1 2000)

high water (HW)

The maximum height reached by a rising tide. The high water is due to the periodic tidal forces and the effects of meteorological, hydrologic, and/or oceanographic conditions. For tidal datum computational purposes, the maximum height is not considered a high water unless it contains a tidal high water. (NOS CO-OPS 1 2000)

high water line

The intersection of the land with the water surface at an elevation of high water. (NOS CO-OPS 1 2000)

high water mark

A line or mark left upon tide flats, beach, or along shore objects indicating the elevation of the intrusion of high water. The mark may be a line of oil or scum on along shore objects, or a more or less continuous deposit of fine shell or debris on the fore shore or berm. This mark is physical evidence of the general height reached by wave run up at recent high waters. It should not be confused with the mean high water line or mean higher high water line. (NOS CO-OPS 1 2000)

I

inland waters

Waters landward of the baseline from which the marginal seas are measured and over which complete sovereignty is exercised. Also known as “internal waters.” (Reed 2000)

inshore

In beach terminology, the zone of variable width between the shoreface and the seaward limit of the breaker zone. (Ellis 1978)

intertidal zone (technical definition)

The zone between the mean higher high water and mean lower low water lines. (NOS CO-OPS 1 2000)

island

A piece of land completely surrounded by water. (Hydrographic Dictionary 1990)

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J

Jus privatum

Private law as distinguished from jus publicum, or public law. The law regulating the rights of individuals. The right, title, or dominion of a private owner. At common law, title to lands below high water mark was in the King as the sovereign, but the dominion was vested in him as the representative of the people and for their benefit. (Shalowitz 1964)

Jus publicum

Public law as distinguished from Jus Privatum or, private law. The right which a sovereign exercises in a public capacity for the benefit of the people, as distinguished from a right exercised in a proprietary capacity. (Shalowitz 1964)

K

No terms

L

latitude

The angular distance between a terrestrial position and the equator measured northward or southward from the equator along a meridian of longitude. (NOS CO-OPS 1 2000)

ledge

A shelf -like projection, on the side of a rock or mountain. A rocky formation continuous with and fringing the shore. (Hydrographic Dictionary 1990)

levee

Artificial bank confining a stream channel or limiting adjacent areas subject to flooding; an embankment bordering a submarine canyon or channel, usually occurring along the outer edge of a curve. (Ellis 1978)

littoral

Bordering on the sea.  (Reed 2000)

Living shorelines

A shoreline management practice that provides erosion control benefits; protects, restores, or enhances natural shoreline habitat; and maintains coastal processes through the strategic placement of plants, stone, sand fill, and other structural organic materials (e.g. biologs, oyster reefs, etc).

local time

Time in which noon is defined by the transit of the Sun over the local meridian as distinguished from standard time which is based upon the transit of the Sun over a standard meridian. Local time may be either mean or apparent, according to whether reference is to the mean or actual Sun. Local time was in general use in the United States until 1883, when standard time was adopted. The use of local time in other parts of the world has also been practically abandoned in favor of the more convenient standard time. (Hicks 1984)

Longitude

Angular distance in a great circle of reference reckoned from an accepted origin to the projection of any point on that circle. Longitude on the Earth's surface is measured on the Equator east and west of the meridian of Greenwich and may be expressed either in degrees or in hours, the hour being taken as the equivalent of 15ﾟof longitude. Celestial longitude is measured in the ecliptic eastward from the vernal equinox. The mean longitude of a celestial body moving in an orbit is the longitude that would be attained by a point moving uniformly in the circle of reference at the same average angular velocity as that of the body, with the initial position of the point so taken that its longitude would be the same as that of the body at a certain specified position in its orbit. With a common initial point, the mean longitude of a body will be the same in whatever circle it may be reckoned. (NOS CO-OPS 1 2000)

low tide

Same as low water. (NOS CO-OPS 1 2000)

low water (LW)

The minimum height reached by a falling tide. The low water is due to the periodic tidal forces and the effects of meteorological, hydrologic, and/or oceanographic conditions. For tidal datum computational purposes, the minimum height is not considered a low water unless it contains a tidal low water. (NOS CO-OPS 1 2000)

low water datum (LWD)

(1) The geopotential elevation (geopotential difference) for each of the Great Lakes and Lake St. Clair and the corresponding sloping surfaces of the St. Marys, St. Clair, Detroit, Niagara, and St. Lawrence Rivers to which are referred the depths shown on the navigational charts and the authorized depths for navigation improvement projects. Elevations of these planes are referred to IGLD (1955) and are Lake Superior 600.0 feet, Lakes Michigan and Huron 576.8 feet, Lake St. Clair 571.7 feet, Lake Erie 568.6 feet, and Lake Ontario 242.8 feet.

(2) An approximation of mean low water that has been adopted as a standard reference for a limited area and is retained for an indefinite period regardless of the fact that it may differ slightly from a better determination of mean low water from a subsequent series of observations. Used primarily for river and harbor engineering purposes. Boston low water datum is an example. (NOS CO-OPS 1 2000)

low water interval (LWI)

See lunitidal interval. (NOS CO-OPS 1 2000)

low-water line

The intersection of the land with the water surface at an elevation of low water. (NOS CO-OPS 1 2000)

lower high water (LHW)

The lower of the two high waters of any tidal day where the tide is of the semidiurnal or mixed type. (Shalowitz 1964)

lower low water (LLW)

The lowest of the low waters (or single low water) of any specified tidal day due to the declination effects of the Moon and Sun. (NOS CO-OPS 1 2000)

lower low water datum (LLWD)

An approximation of mean lower low water that has been adopted as a standard reference for a limited area and is retained for an indefinite period regardless of the fact that it may differ slightly from a better determination of mean lower low water from a subsequent series of observations. Used primarily for river and harbor engineering purposes. Columbia River lower low water datum is an example. (NOS CO-OPS 1 2000)

lunitidal interval

The interval between the Moon's transit (upper or lower) over the local or Greenwich meridian and the following high or low water. The average of all high water intervals for all phases of the Moon is known as mean high water lunitidal interval and is abbreviated to high water interval (HWI). Similarly, mean low water lunitidal interval is abbreviated to low water interval (LWI). The interval is described as local or Greenwich according to whether the reference is to the transit over the local or Greenwich meridian. When not otherwise specified, the reference is assumed to be local. When there is considerable diurnal inequality in the tide, separate intervals may be obtained for the higher high waters, lower high waters, higher low waters, and lower low waters. These are designated respectively as higher high water interval (HHWI), lower high water interval (LHWI), higher low water interval (HLWI), and lower low water interval (LLWI). In such cases, and also when the tide is diurnal, it is necessary to distinguish between the upper and lower transit of the Moon with reference to its declination. Intervals referred to the Moon's upper transit at the time of its north declination or the lower transit at the time of south declination are marked a. Intervals referred to the Moon's lower transit at the time of its north declination or to the upper transit at the time of south declination are marked b. (NOS CO-OPS 1 2000)

M

marine boundary

The mean lower low water line (MLLWL) when used as a boundary. Also, lines used as boundaries seaward of and measured from (or points thereon) the MLLWL. (NOS CO-OPS 1 2000)

mean diurnal tide level (MDTL)

A tidal datum. The arithmetic mean of mean higher high water and mean lower low water. (NOS CO-OPS 1 2000)

mean high water (MHW)

A tidal datum. The average of all the high water heights observed over the National Tidal Datum Epoch.  For stations with shorter series, simultaneous observational comparisons are made with a control tide station in order to derive the equivalent datum of the National Tidal Datum Epoch. (NOS CO-OPS 1 2000)

mean high water line (MHWL)

The line on a chart or map which represents the intersection of the land with the water surface at the elevation of mean high water. (NOS CO-OPS 1 2000)

mean higher high water (MHHW)

A tidal datum. The average of the higher high water height of each tidal day observed over the National Tidal Datum Epoch. For stations with shorter series, simultaneous observational comparisons are made with a control tide station in order to derive the equivalent datum of the National Tidal Datum Epoch. (NOS CO-OPS 1 2000)

mean lower low water (MLLW)

A tidal datum. The average of the lower low water height of each tidal day observed over the National Tidal Datum Epoch. For stations with shorter series, simultaneous observational comparisons are made with a control tide station in order to derive the equivalent datum of the National Tidal Datum Epoch. (NOS CO-OPS 1 2000)

mean sea level (MSL)

A tidal datum. The arithmetic mean of hourly heights observed over the National Tidal  Datum Epoch. Shorter series are specified in the name; e.g., monthly mean sea level and yearly mean sea level. (NOS CO-OPS 1 2000)

mean tide level

Same as half tide level. (NOS CO-OPS 1 2000)

mean low tide

The mean average of all the low tides (high low tides and low low tides) occurring over a certain period of time, usually 18.6 years (one lunar epoch). (Coastal States Organization 1997)

mean lower low water line (MLLWL)

The line on a chart or map which represents the intersection of the land with the water surface at the elevation of mean lower low water. (NOS CO-OPS 1 2000)

mean range of tide (Mn)

The difference in height between mean high water and mean low water. (NOS CO-OPS 1 2000)

mean water level line (MWLL)

The line on a chart or map which represents the intersection of the land with the water surface at the elevation of mean water level. (NOS CO-OPS 1 2000)

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N

National Geodetic Vertical Datum of 1929 [NGVD (1929)]

A fixed reference adopted as a standard geodetic datum for elevations determined by leveling. The datum was derived for surveys from a general adjustment of the first-order leveling nets of both the United States and Canada. In the adjustment, mean sea level was held fixed as observed at 21 tide stations in the United States and 5 in Canada. The geodetic datum now in use in the United States is the National Geodetic Vertical Datum. The year indicates the time of the general adjustment. A synonym for Sea-level Datum of 1929. The geodetic datum is fixed and does not take into account the changing stands of sea level. Because there are many variables affecting sea level, and because the geodetic datum represents a best fit over a broad area, the relationship between the geodetic datum and local mean sea level is not consistent from one location to another in either time or space. For this reason, the National Geodetic Vertical Datum should not be confused with mean sea level. NGVD(1929) has been superceded for use by NAVD88. (NOS CO-OPS 1 2000)

National Tidal Datum Convention of 1980

Effective November 28, 1980, the Convention: (1) establishes one uniform, continuous tidal datum system for all marine waters of the United States, its territories, Commonwealth of Puerto Rico, and Trust Territory of the Pacific Islands, for the first time in its history; (2) provides a tidal datum system independent of computations based on type of tide; (3) lowers chart datum from mean low water to mean lower low water along the Atlantic coast of the United States; (4) updates the National Tidal Datum Epoch from 1941 through 1959, to 1960 through 1978; (5) changes the name Gulf Coast Low Water Datum to mean lower low water; (6) introduces the tidal datum of mean higher high water in areas of predominantly diurnal tides; and (7) lowers mean high water in areas of predominantly diurnal tides. See chart datum. (NOS CO-OPS 1 2000)

National Tidal Datum Epoch

The specific l9-year period adopted by the National Ocean Service as the official time segment over which tide observations are taken and reduced to obtain mean values (e.g., mean lower low water, etc.) for tidal datums. It is necessary for standardization because of periodic and apparent secular trends in sea level. The present National Tidal Datum Epoch is 1960 through 1978. It is reviewed annually for possible revision and must be actively considered for revision every 25 years. (NOS CO-OPS 1 2000)

National Water Level Observation Network (NWLON)

The network of tide and water level stations operated by the National Ocean Service along the marine and Great Lakes coasts and islands of the United States. The NWLON is composed of the primary and secondary control tide stations of the National Ocean Service. Distributed along the coasts of the United States, this Network provides the basic tidal datums for coastal and marine boundaries and for chart datum of the United States. Tide observations at a secondary control tide station or tertiary tide station are reduced to equivalent l9-year tidal datums through the comparison of simultaneous observations with a primary control tide station. In addition to hydrography and nautical charting, and to coastal and marine boundaries, the Network is used for coastal processes and tectonic studies, tsunami and storm surge warnings, and climate monitoring. The National Water Level Observation Network also includes stations operated throughout the Great Lakes Basin. The primary network is composed of 54 sites with 139 seasonal gauge sites selectively operated 4 months annually for the maintenance of IGLD. The network supports regulation, navigation and charting, river and harbor improvement, power generation, various scientific activities, and the adjustment for vertical movement of the Earth's crust in the Great Lakes Basin. (NOS CO-OPS 1 2000)

navigable waters

Waters that are either tidally influenced or navigable in fact. (Reed 2000)

navigability

The actual navigable capacity of a waterway and not the extent of tidal influence. (Shalowitz 1962)

neap tides

Tides of decreased range or tidal currents of decreased speed occurring semimonthly as the result of the Moon being in quadrature. The neap range (Np) of the tide is the average range occurring at the time of neap tides and is most conveniently computed from the harmonic constants. It is smaller than the mean range where the type of tide is either semi diurnal or mixed and is of no practical significance where the type of tide is predominantly diurnal. The average height of the high waters of the neap tide is called neap high water or high water neaps (MHWN) and the average height of the corresponding low waters is called neap low water or low water neaps (MLWN). (NOS CO-OPS 1 2000)

normal tide

A nontechnical term synonymous with tide; i.e., the rise and fall of the ocean due to the gravitational interactions of the Sun, Moon, and Earth alone. Use of this term is discouraged. (Hicks 1984)

North American Vertical Datum of 1988 (NAVD 88)

A fixed reference for elevations determined by geodetic leveling. The datum was derived from a general adjustment of the first-order terrestrial leveling nets of the United States, Canada, and Mexico. In the adjustment, only the height of the primary tidal bench mark, referenced to the International Great Lakes Datum of 1985 (IGLD 85) Local mean sea level height value, at Father Point, Rimouski, Quebec, Canada was held fixed, thus providing minimum constraint. NAVD 88 and IGLD 85 are identical. However, NAVD 88 bench mark values are given in Helmert orthometric height units while IGLD 85 values are in dynamic heights. See International Great Lakes Datum of 1985, National Geodetic Vertical Datum of 1929, and geopotential difference. (Hicks 1984)

O

ordinary high water line

Same as mean high water line. (Shalowitz 1962)

ordinary low water mark

A term used by the Supreme Court in the submerged lands case in indicate where federal paramount rights begin in the offshore submerged lands, and which the Special Master in the California case was called upon to interpret with respect to the type of tide found along the California coast. The intersection of the tidal plane of mean low water with the shore. (Shalowitz 1962)

P

photogrammetry

The science or art of obtaining reliable measurements from photographs. (Hydrographic Dictionary 1990)

precision

The degree of refinement of a value not to be confused with accuracy, which is the degree of conformance with the correct value. (Hydrographic Dictionary 1990)

Prima facie public trust lands

Lands that appear to be subject to the Public Trust Doctrine in that they lay beneath tidal or navigable-in-fact waters below the ordinary high water mark. (Coastal States Organization 1997)

public trust servitude

The bundle of rights held by the public to use and enjoy privately held trust lands for certain public purposes. The burden on the subordinate jus privatum owner by the dominant jus publicum interest of the public. (Coastal States Organization 1997)

Q

No terms

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R

range of tide

The difference in height between consecutive high and low waters. The mean range is the difference in height between mean high water and mean low water. The great diurnal range or diurnal range is the difference in height between mean higher high water and mean lower low water. For other ranges see spring, neap, perigean, apogean, and tropic tides; and tropic ranges. (NOS CO-OPS 1 2000)

real-time

Pertains to a data collecting system that controls an on-going process and delivers its outputs (or controls its inputs) not later than the time when these are needed for effective control. (NOS CO-OPS 1 2000)

recession

Continuing landward movement of the shoreline ; a net landward movement of the shoreline over a specified period. (Ellis 1978)

reduction of tides or tidal currents

A processing of observed tide or tidal current data to obtain mean values for tidal or tidal current constants. (NOS CO-OPS 1 2000)

reference station

A tide or current station for which independent daily predictions are given in the "Tide Tables" and "Tidal Current Tables," and from which corresponding predictions are obtained for subordinate stations by means of differences and ratios. See subordinate tide station (2) and subordinate current station (2). (NOS CO-OPS 1 2000)

riparian

Associated with or appurtenant to shorelands of non-tidal waters. (Coastal States Organization 1997)

riparian rights

The rights of an owner of land bordering a river or the sea and relates to the water (its use), ownership of the shore, right of ingress and egress, accretions, etc. (Shalowitz 1962)

S

sea level (water level)

Height of the surface of the sea at any time. (Ellis 1978)

sea level datum (SLD)

An obsolete term. See National Geodetic Vertical Datum of 1929 and mean sea level. (Hicks 1984)

secondary control tide station

A tide station at which continuous observations have been made over a minimum period of 1 year but less than 19 years. The series is reduced by comparison with simultaneous observations from a primary control tide station. This station provides for a 365-day harmonic analysis including the seasonal fluctuation of sea level. See tide station, primary control tide station, tertiary tide station, and subordinate tide station (1). (NOS CO-OPS 1 2000)

semidiurnal

Having a period or cycle of approximately one-half of a tidal day. The predominant type of tide throughout the world is semi diurnal, with two high waters and two low waters each tidal day. The tidal current is said to be semi diurnal when there are two flood and two ebb periods each day. A semi diurnal constituent has two maxima and two minima each constituent day, and its symbol is the subscript 2. (NOS CO-OPS 1 2000)

shore profile

Intersection of the shore with a vertical plane that is perpendicular to the shoreline. The profile may extend from the top of the dune line to the seaward limit of sand movement; but for shoreline mapping purposes, extends from the berm crest offshore to the mean low water line or mean lower low water line. (Ellis 1978)

shorelands

General term including tidelands and navigable freshwater shores below the ordinary high water mark. (Coastal States Organization 1997)

shoreline (coastline)

The intersection of the land with the water surface. The shoreline shown on charts represents the line of contact between the land and a selected water elevation. In areas affected by tidal fluctuations, this line of contact is the mean high water line. In confined coastal waters of diminished tidal influence, the mean water level line may be used. The shoreline is defined as MHW. (NOS CO-OPS 1 2000)

slack water (slack)

The state of a tidal current when its speed is near zero, especially the moment when a reversing current changes direction and its speed is zero. The term also is applied to the entire period of low speed near the time of turning of the current when it is too weak to be of any practical importance in navigation. The relation of the time of slack water to the tidal phases varies in different localities. For a perfect standing tidal wave, slack water occurs at the time of high and of low water, while for a perfect progressive tidal wave, slack water occurs midway between high and low water. See slack; ebb begins and slack; flood begins. (Hicks 1984)

slack; ebb begins (slack before ebb)

The slack water immediately preceding the ebb current. (Hicks 1984)

small diurnal range (Sl)

Difference in height between mean lower high water and mean higher low water. (NOS CO-OPS 1 2000)

spring high water

Same as mean high water springs (MHWS). See spring tides. (NOS CO-OPS 1 2000)

spring low water

Same as mean low water springs (MLWS). See spring tides. (NOS CO-OPS 1 2000)

spring range (Sg)

See spring tides. (NOS CO-OPS 1 2000)

spring tides

Tides of increased range or tidal currents of increased speed occurring semimonthly as the result of the Moon being new or full. The spring range (Sg) of tide is the average range occurring at the time of spring tides and is most conveniently computed from the harmonic constants. It is larger than the mean range where the type of tide is either semi diurnal or mixed, and is of no practical significance where the type of tide is predominantly diurnal. The average height of the high waters of the spring tides is called spring high water or mean high water springs (MHWS) and the average height of the corresponding low waters is called spring low water or mean low water springs (MLWS).  (NOS CO-OPS 1 2000)

stand of tide

Sometimes called a platform tide. An interval at high or low water when there is no sensible change in the height of the tide. The water level is stationary at high and low water for only an instant, but the change in level near these times is so slow that it is not usually perceptible. In general, the duration of the apparent stand will depend upon the range of tide, being longer for a small range than for a large range, but where there is a tendency for a double tide the stand may last for several hours even with a large range of tide. (NOS CO-OPS 1 2000)

standard time

A kind of time based upon the transit of the Sun over a certain specified meridian, called the time meridian, and adopted for use over a considerable area. With a few exceptions, standard time is based upon some meridian which differs by a multiple of 15ø from the meridian of Greenwich. The United States first adopted standard time in 1883 on the initiative of the American Railway Association, and at noon on November 18 of that year the telegraphic time signals from the Naval Observatory at Washington were changed to this system. (Hicks 1984)

submerged lands

Lands covered by water at any stage of the tide. (NOS CO-OPS 1 2000)

subordinate tide station

(1) A tide station from which a relatively short series of observations is reduced by comparison with simultaneous observations from a tide station with a relatively long series of observations. See tide station, primary control tide station, secondary control tide station, and tertiary tide station.

(2) A station listed in the Tide Tables from which predictions are to be obtained by means of differences and ratios applied to the full predictions at a reference station. See reference station. (NOS CO-OPS 1 2000)

T

temporal variation

Any change in the Earth's magnetic field which is a function of time. Also referred to as magnetic temporal variation. (Hydrographic Dictionary 1990)

territorial sea

The offshore belt in which a coastal state has exclusive jurisdiction.  The territorial sea may not extend more than 12 nautical miles from the coast line. (Reed 2000)

tertiary tide station

A tide station at which continuous observations have been made over a minimum period of 30 days but less than 1 year. The series is reduced by comparison with simultaneous observations from a secondary control tide station. This station provides for a 29-day harmonic analysis. See tide station, primary control tide station, secondary control tide station, and subordinate tide station (1). (NOS CO-OPS 1 2000)

tidal estuary

See estuary. (NOS CO-OPS 1 2000)

tidal gauge

A devise for measuring the height of tide. A graduated staff in a sheltered area where visual observations can be made; or it may consist of an elaborate recording instrument making a continuous graphic record of tide height against time. Such an instrument is usually actuated by a float in a pipe communicating with the sea through a small hole which filters out shorter waves. (Hydrographic Dictionary 1990)

tidal zoning

The practice of dividing a hydrographic survey area into discrete zones or sections, each one possessing similar tidal characteristics. One set of tide reducers is assigned to each zone. Tide reducers are used to adjust the soundings in that zone to chart datum (MLLW). Tidal zoning is necessary in order to correct for differing water level heights occurring throughout the survey area at any given time. Each zone of the survey area is geographically delineated such that the differences in time and range do not exceed certain limits, generally 0.2 hours and 0.2 feet respectively; however, these limits are subject to change depending upon type of survey, location, and tidal characteristics. The tide reducers are derived from the water levels recorded at an appropriate tide station, usually nearby. Tide reducers are used to correct the soundings throughout the hydrographic survey area to a common, uniform, uninterrupted chart datum. (NOS CO-OPS 1 2000)

tide mark

High-water mark left by tidal water; the highest point reached by high tide; a mark placed to indicate the highest point reached by a high tide, or occasionally, any specified stage of tide (Ellis 1978)

tide staff

A tide gauge consisting of a vertical graduated staff from which the height of the tide can be read directly. It is called a fixed staff when secured in place so that it cannot be easily removed. A portable staff is one that is designed for removal from the water when not in use. For such a staff a fixed support is provided The support has a metal stop secured to it so that the staff will always have the same elevation when installed for use. (NOS CO-OPS 1 2000)

tide (water level) station

The geographic location at which tidal observations are conducted. Also, the facilities used to make tidal observations. These may include a tide house, tide gauge, tide staff, and tidal bench marks. See primary control tide station, secondary control tide station, tertiary tide station, and subordinate tide station. (NOS CO-OPS 1 2000)

tide tables

Tables which give daily predictions of the times and heights of high and low waters. These predictions are usually supplemented by tidal differences and constants through which predictions can be obtained for numerous other locations. (NOS CO-OPS 1 2000)

tidelands

The zone between the mean high water and mean low water lines. It is identical with intertidal zone (technical definition) when the type of tide is semi diurnal or diurnal. (NOS CO-OPS 1 2000)

tidewaters

Water activated by the tide generating forces and/or water affected by the resulting tide, especially in coastal and estuarine areas. Also, a general term often applied to the land and water of estuarine areas formed by postglacial drowning of coastal plain rivers. (NOS CO-OPS 1 2000)

type of tide

A classification based on characteristic forms of a tide curve. Qualitatively, when the two high waters and two low waters of each tidal day are approximately equal in height, the tide is said to be semidiurnal; when there is a relatively large diurnal inequality in the high or low waters or both, it is said to be mixed; and when there is only one high water and one low water in each tidal day, it is said to be diurnal. Quantitatively (after Dietrich), where the ratio of K1 + O1 to M2 + S2 is less than 0.25, the tide is classified as semidiurnal; where the ratio is from 0.25 to 1.5, the tide is mixed, mainly semidiurnal; where the ratio is from 1.5 to 3.0, the tide is mixed, mainly diurnal; and where greater than 3.0, diurnal. (NOS CO-OPS 1 2000)

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U

universal time (UT)

Same as Greenwich mean time (GMT). (NOS CO-OPS 1 2000)

upland

Land above the mean high water line (shoreline) and subject to private ownership, as distinguished from tidelands, the ownership of which is prima facie in the state but also subject to divestment under state statutes. See tidelands. (NOS CO-OPS 1 2000)

V

No terms

W

wash

The visible or audible motion of agitated water; especially that caused by the passage of a vessel. (Hydrographic Dictionary 1990)

waterline

Juncture of land and sea. This line fluctuates, changing with the tide or other fluctuations in the water. (Ellis 1978)

wet sand beach

Area between the ordinary high tide and the ordinary low tide lines. (Coastal States Organization 1997)

World Geodetic System

A global geodesic reference system developed by the USA for satellite position fixing and recommended by the IHO for hydrographic and cartographic use. (Hydrographic Dictionary 1990)

X, Y, Z

No terms

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