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Revision papers with worked solutions
Published in Philip M. Smith, Tides, 2018
Explain the meanings of the following terms: DRYING HEIGHT: The height of the seabed exposed above Chart Datum at LAT.HAT: The highest ever expected levels of High Water given the worst combination of meteorological conditions and Spring Tides.CHARTED DEPTH: The depths marked on a chart to indicate the depth from Chart Datum down to the seabed.MLWS: The average of the lowest Low Waters recorded during Spring Tides.CHART DATUM: The point at which the level of the water level will not normally be expected to drop below. It is normally, but not always, coincident with the level of Lowest Astronomical Tide (LAT). It is the reference level for Heights of Tide, Charted Depths and other levels such as MHWS, MLWS. MLWN, MHWN and Mean Sea Level (MSL).
Basic Characteristics of Tides and Tidal Propagation
Published in S.N. Ghosh, Tidal Hydraulic Engineering, 2017
The measurement of tide is very important for practical engineering purposes as well as for tide of prediction. The most important purpose is construction navigational charts, for which echo-sounding surveys have to be based on a datum. In coastal areas the reference level, commonly termed as the sounding datum, is usually fixed at the level of the lowest predicted tide. Sometimes the reference level or the sounding datum is a chart datum fixed at a certain tide level. The sounding datum may be a totally arbitrary, level, but is always expressed as a certain distance below a permanent mark. such as a bench-mark of the land levelling system or the sill of a dock. Once this has been done tide measurements will need to be taken during the surveys. Secondly, to provide predictions for navigational purposes it is necessary to have continuous records, as many estuaries show considerable changes in water level with atmospheric pressure and wind. For the navigation of vessels with minimum underkeel clearance it is necessary to provide actual levels rather than predicted levels. Thirdly. for prediction of tides tidal records for a period of one year are required, although ideally it should be for nineteen years. This will provide the astronomical constants for prediction.
NOAA’s national water level observation network (NWLON)
Published in Journal of Operational Oceanography, 2019
NWLON supports the vertical reference system of tidal datums for the nation. A tidal datum is defined in terms of a certain phase of the tide (Mean Low Water [MLW], Mean Higher High Water [MHHW], etc.) and is based on a 19-year period of water level averaging called the National Tidal Datum Epoch (NTDE). The present NTDE adopted by NOAA/National Ocean Service (NOS) in the United States is 1983 through 2001. This specific 19-year period is the official time segment over which sea level observations are taken and reduced to obtain mean values for datum definition. Water level (tidal) datums are local vertical datums, which may change considerably within a geographical area due to changes in tidal hydrodynamics and range of tide. Therefore, maintaining the density of NWLON stations along the coast is critical for maintaining the national spatial reference framework. Datums are referenced to fixed points on land, known as bench marks, with data provided about these marks made available through bench mark data sheets. The NTDE must be actively considered for revision every 25 years; CO-OPS is currently planning the next NTDE update to be initiated in 2020. In nontidal areas like the Great Lakes, water level and chart datum elevations are presently referenced to International Great Lakes Datum of 1985.
Development of Saudi continuous chart datum: Arabian Gulf case study
Published in Geomatics, Natural Hazards and Risk, 2019
Mohammed El-Diasty, Salim Al-Harbi, Spiros Pagiatakis
A continuous chart datum is a two-dimensional reference surface relative to a continuous vertical reference datum such as the Lowest Astronomical Tide (LAT) in Saudi Arabia or the reference ellipsoid (WGS84). It is realized by numerous hydrographic organizations around the world that the hydrographic vertical datum, such as a chart datum, now requires a continuous treatment. These continuous chart datums exist, most notably at the National Oceanic and Atmospheric Administration (NOAA’s VDatum datum, Gesch and Wilson 2001), the United Kingdom Hydrographic Office (UKHO’s VORF datum, Adams 2006; Iliffe et al. 2013), the Service Hydrographique et Oceanographique de la Marine (SHOM’s BATHYELLI datum, Pineau-Guillou and Dorst 2011), the Australian Hydrographic Service (AHS’s AusCoastVDT, Keysers, et al. 2013), Canadian Hydrographic Service (CHS’s CCVD datum, (Lefaivre, et al. 2010; De Lange 2012; Robin et al. 2012, 2016; ) and Dutch and Belgium vertical reference datum (NEVREF, Slobbe, et al. 2018). In this paper, the Saudi coastal mapping and monitoring (SCM2RS) group takes a lead in developing a Saudi continuous chart datum (SCCD) using the data collected from Saudi coastal areas along with the hydrodynamic ocean model.
A causative analysis on ECDIS-related grounding accidents
Published in Ships and Offshore Structures, 2020
İdris Turna, Orkun Burak Öztürk
According to Table 2, it is indicated that only 0.7% of the ENC charts that belong to coastal areas, in which running-aground accidents frequently occur, are described as an A1 region which is the most trusted category. It is known that the water surface levels also known as chart datum that is accepted as references for the soundings and vertical datum varies in the INT-type charts that are produced by the national hydrographic offices. It is notable that while some hydrographic offices prefer Lowest Astronomical Tide or Mean Low Water Spring (MLWS) for soundings, Mean Sea Level is preferred as a chart datum in others. Figure 3 shows the information of an ENC chart in which the MSL water level is preferred for soundings and vertical datum.