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Topic: Lowest astronomical tide

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	Chart datum - Wikipedia, the free encyclopedia
		The chart datum is the level of water that charted depths displayed on nautical charts are measured from.
		Chart datum is height of water at the lowest possible theoretical tide also known as the lowest astronomical tide (commmonly abbreviated to "LAT").
		To calculate whether an area that dries is under water, subtract the drying height from the height of the tide.
	en.wikipedia.org /wiki/Chart_datum (168 words)

	Tides
		Tides are the periodic rise and fall, or vertical movement of the levels of the worlds oceans.
		Tides are generated by the effect on the Earth's oceans by gravitational forces between the earth, the moon and the sun, by centrifugal force due to the Earth's rotation, and by centrifugal force due to the Earth's solar orbit.
		This is the lowest astronomical tide recorded over a solar cycle of 18.6 years, and is the datum or reference point for all soundings on charts and tidal heights.This fact is clearly noted in the tide tables.
	users.tpg.com.au /users/vmrg/Tides.html (1502 words)

	Definition of VERDAT
		lowest low water: an arbitrary level conforming to the lowest tide observed at a place, or some what lower.
		lowest low water springs: an arbitrary level conforming to the lowest water level observed at a place at spring tides during a period of time shorter than 19 years.
		A tidal datum approximating the lowest water level observed at a place, originated by G.H. Darwin for the tides of India at a level below MSL being equal to the sum of amplitudes of the harmonic constituents M2, S2, K1 and O1; usually below that of the lower low water at spring tides.
	www.caris.com /S-57/attribut/def/d-verdat.htm (786 words)

	MSQ - Tides - notes and definitions (Site not responding. Last check: 2007-09-09)
		The height of the tide, in metres and decimals, is reckoned from the port datum (lowest astronomical tide datum).
		The rise of the tide is the height of the high water above port datum.
		The range of the tide is the difference between the height of high water and the next succeeding or last preceding low water.
	www.msq.qld.gov.au /qt/msq.nsf/index/tides_notes (1301 words)

	Tidal Reference Frame For Queensland (Site not responding. Last check: 2007-09-09)
		The tides at all of the stations within a region must be assigned to the same form as the tidal reference frame station in the region.
		Semidiurnal Tides In those regions where the semidiurnal components of the tide dominate, it is proposed to rely on correlation and regression analysis to deduce the tidal “rise ratio and constant” or the related "amplitude ratio and constant" for the high and low tide heights at the secondary station and the relevant reference station.
		Diurnal Tides Even in those regions where the diurnal component of the tide dominates, and the form of the tide is clearly diurnal, the degree of diurnality changes significantly over relatively short distances.
	www.icsm.gov.au /icsm/tides/SP9/links/msq_tidalreferenceframe.htm (4826 words)

	Taming the Tide
		However, because the exact nature of the relationship between the Moon and tides is concealed behind many complex factors, it has taken eminent scientists from centuries past and present to develop our understanding of tide calculations, and the prediction of tides.
		The most common tide type is the semi-diurnal tide This type is mostly influenced by the summing of the gravitational effects of the Moon over the Earth, and the centrifugal force produced by the rotation of the Earth & Moon.
		Many ports do however, exhibit a tide lead or a lag time of a few hours or perhaps even days, this phenomenon is commonly called the age of the tide.
	www.flyflickers.com /ff/articles/effs/tides.htm (2244 words)

	Metocean Glossary
		The average of the higher "Highest astronomical tide" heights of each tidal oscillation observed over a period of 19 years.
		The average of the "Highest astronomical tide" heights observed over the duration of "Tide periodicity".
		Midpoint between the "Lowest astronomical tide" and the "Highest astronomical tide".
	www.ifremer.fr /web-com/glossary/glossa39.htm (287 words)

	Geoscience Australia: Marine & Coastal - Maritime Boundaries Computation
		Lowest Astronomical Tide is the lowest level to which sea level can be predicted to fall under normal meteorological conditions.
		It would be a laborious and costly exercise to determine an exact LAT along all of Australia's vast coastline and therefore a best estimate is usually based on current charting, topographic maps, satellite imagery, and other sources.
		Physical changes to the coast and improved methods of locating the LAT line in the future may lead to differences between the TSB and the information depicted on charts in certain areas.
	www.ga.gov.au /nmd/mapping/marbound/computation.jsp (652 words)

	Shoreline management coastal processes tides
		Tides are the periodic rise and fall of the ocean waters.
		As the basic driving forces behind the tides are astronomical the tide times and levels are predictable.
		In areas with large tidal ranges, boats anchored at high tide are often left stranded on the dry beach at low tide.
	www.seftoncoast.org.uk /shore_tides.html (866 words)

	CHL - CEM Appendix A - Glossary of Coastal Terminology
		In shallow estuaries where the range of tide is large, the high water is propagated inward faster than the low water because of the greater depth at high water.
		A tide GAUGE that is operated by a float in a long vertical box to which the tide is admitted through an opening in the bottom.
		The part of the shore, lying between the crest of the seaward berm (or upper limit of wave wash at high tide) and the ordinary low-water mark, that is ordinarily traversed by the uprush and backrush of the waves as the tides rise and fall.
	chl.erdc.usace.army.mil /CHL.aspx?p=s&a=ARTICLES;102 (11370 words)

	National Tidal & Sea Level Facility (Site not responding. Last check: 2007-09-09)
		LAT - lowest astronomical tide, MHWN - mean high water neaps, MLWN - mean low water neaps,
		The tide gauge is located within the Port Control building on West Pier, Newhaven, and the measuring points are located on the pier wall, southwest of the Port Control building.
		The bubbler system supplies two full tide and one mid tide pressure points which are mounted on steelwork attached to the pier wall.
	www.pol.ac.uk /ntslf/tgi/newh.html (199 words)

	EasyTide - on-line tidal predictions from the UKHO
		First the behaviour of the tide has to be recorded by a tide gauge at each particular location and the results subsequently analysed.
		HAT and LAT are not the extreme levels which can be reached, as Storm Surges (wind-induced long period waves causing higher and lower-than-predicted levels to occur) and pressure effects can significantly alter the times and / or heights of the observed tide.
		When this range is at its greatest the tides are referred to as 'Spring tides' and when the range is at its smallest the tides are 'Neap tides'.
	easytide.ukho.gov.uk /easytide/EasyTide/Support/faq.aspx (2202 words)

	IHE Delft - Dicea (Site not responding. Last check: 2007-09-09)
		The height of mean low water springs is the average height obtained by the two successive low waters during the same periods.
		The height of mean low water nears is the average height obtained by the two successive low waters during the same periods.
		Lowest part of sea- and portside breakwater slope, generally forming the transition to the seabed.
	www.ihe.nl /we/dicea/int01/glosT.htm (440 words)

	Manly Hydraulics Laboratory (Site not responding. Last check: 2007-09-09)
		The actual tide may differ from the predicted tide due to meteorological and oceanographic conditions.
		Zero on the tide plot is Sydney Camp Cove Datum, which is approximately the level of the Lowest Astronomical Tide.
		Important: These predictions have been generated from data recorded by MHL and are NOT the official tide predictions for Sydney and should not be used for navigational purposes.
	www.mhl.nsw.gov.au /www/sydp_tide.htmlx (146 words)

	Guide to tidal abbreviations - Marine safety - DPI - NT Government - Australia - Microsoft Internet Explorer (Site not responding. Last check: 2007-09-09)
		HAT and LAT are not the extreme levels that can be reached, as storm surges may cause considerably higher and low levels to occur.
		The average throughout a year of the heights of two successive highwaters when the range of tide is the least, at the time of first and last quarter of the moon.
		The range of the tide is the difference between the height of “High Water” and the next succeeding or last proceeding “Low Water”.
	www.ipe.nt.gov.au /whatwedo/marinesafety/publications/safety/tidalabbreviations.html (404 words)

	Chart Soundings
		They are collected at different points in the tide cycle and must be corrected so they all relate to a common reference point.
		Several methods are used and you must check which one your chart and tide tables are using.
		LAT: Lowest Astronomical Tide is the theoretically lowest water level achieved by astronomical influences.
	www.sailingusa.info /chart_soundings.htm (143 words)

	Frequently Asked Questions
		A: Tide heights are given relative to the "datum" which in most cases is one of several benchmarks corresponding to low tides of varying extremeness.
		LAT is the lowest tide predicted over a 19 year period.
		The two astronomical bodies are held together by gravitational attraction, but are simultaneously kept apart by an equal and opposite centrifugal force produced by their individual revolutions around the center-of-mass of the earth-moon system.
	www.flaterco.com /xtide/faq.html (5005 words)

	COASTCHART Project
		The term 'tide' correctly refers only to relatively short-period, astronomically induced vertical changes in the height of the sea surface.
		Tides represent the rise and fall of the surface of the seas and oceans primarily due to the gravitational pull of the moon and sun on the rotating Earth, which results in two daily high and two low tides in the study area.
		The vertical chart datum is often set to Lowest Astronomical Tide (LAT) - the lowest predicted tide, disregarding exceptional weather conditions.
	www.logicacmg.com /coastchart/project.aspx@SubPageNum=5.html (476 words)

	Metocean Glossary
		The lowest of the "Highest astronomical tide" levels of a tidal oscillation.
		The lowest of the "Low water" levels of a tidal oscillation.
		The lowest tide level over the duration of "Tide periodicity".
	www.ifremer.fr /web-com/glossary/glossa38.htm (88 words)

	marksGB (Site not responding. Last check: 2007-09-09)
		Usually, tide prediction programmes calculate the height of the tide above a reference height called Chart Datum.
		It can be considered as a local variable, defined as ‘a level so low that the tide will not frequently fall below it’, and which is very close to the Lowest Astronomical Tide (LAT).
		Because the programme also displays the height of the tide, one can see immediately if the situation is clear or not.
	p.pellot.free.fr /theomark/marksgb.htm (325 words)

	Tidal information - Marine safety - DPI - NT Government - Australia - Microsoft Internet Explorer (Site not responding. Last check: 2007-09-09)
		In accordance with modern hydrographic practice, the official tidal predictions and Mean Tidal Planes in these tables are referred to the datum of Lowest Astronomical Tide.
		The height of the tide in metres and decimals is reckoned from the lowest astronomical tide.
		Tide tables for the Northern Territory are available from http://www.ipe.nt.gov.au/whatwedo/marinesafety/tides/index.html or contact the Marine Safety Branch.
	www.ipe.nt.gov.au /whatwedo/marinesafety/publications/safety/tidal.html (315 words)

	Term (Site not responding. Last check: 2007-09-09)
		The arithmetic mean of hourly heights of the sea at the tidal station observed over a period of time (preferably 19 years).
		The average of all low water observations at the time of spring tide over a period of time (preferably 19 years).
		The lowest tide level which can be predicted to occur under average meteorological conditions and under any combination of astronomical conditions
	members.optusnet.com.au /cysop/tides.htm (251 words)

	ReductivlakkenLAT (Site not responding. Last check: 2007-09-09)
		This plane, which is based on astronomical predictions, in general for The Netherlands is a lower plane than the current chart datum based on MLLWS.
		This implies that on a chart using LAT as chart datum the depths will be generally less than the same area charted with MLLWS as chart datum.
		The average difference between MLLWS and LAT is about 1 to 2dm, but can be as large as 5dm in the Westerschelde.
	www.hydro.nl /pgs/en/GenG_P8A.htm (133 words)

	ICSM - PERMANENT COMMITTEE TIDES AND SEA LEVEL
		Highest Astronomical Tide: The highest level of water which can be predicted to occur under any combination of astronomical conditions.
		Lowest Astronomical Tide (LAT): The lowest tide level which can be predicted to occur under average meteorological conditions and under any combination of astronomical conditions.
		It should be noted that variation of these definitions might apply in current legislation. It should also be noted that some jurisdictions have adopted pragmatic procedures to approximate these values in the field (eg.
	www.icsm.gov.au /tides/tidal_interface.html (633 words)

	Tidal Levels - Definitions and Notes > Port of London
		The highest and lowest levels respectively which can be predicted to occur under average meteorological conditions and under any combination of astronomical conditions; these levels will not be reached every year.
		Since the combined tidal force is increased the high tides are higher and the low tides are lower than average.
		The values of Lowest Astronomical Tide (LAT) and Highest Astronomical Tide (HAT) are determined by inspection over a span of years.
	www.portoflondon.co.uk /display_fixedpage.cfm/id/265/site/maritime (615 words)

	Newsflash (Site not responding. Last check: 2007-09-09)
		According to international agreement it will be replaced by the height of lowest astronomical tide (LAT) progressively on new editions of the charts during the coming years.
		LAT is 0.3 to 0.6 m lower than MLWS at most German tide stations.
		Therefore, if the level used as chart datum on a German chart is still MLWS, it is sufficient, to subtract half a meter from the predicted height of tide, before adding it to the charted depth to obtain the depth of water available.
	www.bsh.de /Vorlagen/ressources/Druckversion.jsp?_PRINTPAGE_=yes&_PRINTOID_=44813 (175 words)

	LINZ - Tide Levels and Datums
		As a consequence of the annual variation of the tidal levels, the variation in the ranges of the spring and neap tides over the 19 year cycle is twice that of the levels.
		The value of MSL for each port has been derived from the analysis of tidal observations made at the port during the period given in the table in the Tidal Prediction Information document (pdf 16KB).
		When meteorological conditions lower the sea level, the tide will fall below the predicted low water heights, and at a place where Chart Datum is at a comparatively high level, the actual depths at or near low water may be considerably less than charted.
	www.hydro.linz.govt.nz /tides/info/tideinfo5/index.asp (1235 words)

	EDCS Reference Manual
		The first season of the year, or that between winter and summer, reckoned astronomically from the vernal equinox to the summer solstice; i.e.
		The third season of the year, or that between summer and winter, reckoned astronomically from the autumnal equinox to the winter solstice; i.e.
		The fourth and coldest season of the year, coming between autumn and spring; reckoned astronomically from the winter solstice to the vernal equinox; i.e.
	www.sedris.org /sdk_3.1.1/src/lib/edcs/docs/dictionary/EAC_S.htm (5562 words)

	Glossary (Site not responding. Last check: 2007-09-09)
		The inclination of a moon's orbit is the angle between the plane of its orbit and the plane of its primary's equator.
		For example, the moon does not rotate around the earth’s equator, but follows an orbit that is inclined in relation to the earth’s axis, which has an important effect on tides.
		For a reservoir with a fixed overflow sill it is the lowest crest level of that sill.
	www.coastalresearch.nl /glossary.htm (7940 words)

	Hydrographic Survey Notes > Port of London
		This level approximates to Lowest Astronomical Tide (L.A.T.) which is the lowest level that can be predicted to occur under average meteorological conditions and under any combination of astronomical conditions.
		The PLA provides tables of tide predictions and actual, real-time tidal levels at various tide stations along the river and out to the estuary.
		The levels of both the predicted tide and the actual tide are measured from chart datum.
	www.portoflondon.co.uk /display_fixedpage.cfm/id/264/site/maritime (538 words)

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