Tidal Level & Datums

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Author:
mardiellen
ID:
201721
Filename:
Tidal Level & Datums
Updated:
2013-02-19 05:37:25
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Tidal Level & Datums
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  1. Principles of Tidal Datum in Terms of Hydrographic Survey
    The Hydrographer must be able to relate all measured depths (regardless of the stage of tide or level of water at the time of sounding) to a common plane or datum.
  2. Mean Sea Level
    The arithmetic mean of hourly height of the sea at the tidal station observed over a period of time. (18.6yrs)
  3. Mean Tide Level
    Is the mathematical average of the average high & low waters over a period of time.
  4. Highest Astronomical Tide
    The highest level of water that can be predicted to occur under any combination of astronomical conditions.
  5. Lowest Astronomical Tide
    The lowest tide level which can be predicted to occur under the meteorological conditions and under any combination of astronomical conditions.
  6. Mean High/Low Water Springs
    Is the average of all high/low water observations at the time of spring tide over a period of time (18.6yrs). Applicable in Semi-diurnal water only.
  7. Mean High Water Neaps
    Is the average of all high water observations at the time of neap tides over a period of time (18.6yrs). Applicable in Semi-diurnal waters only.
  8. Mean Low Water Neaps
    Is the average of all low water observations at the time of a  neap tide over a period of time (18.6yrs). Applicable in Semi-diurnal waters only.
  9. Sounding Datum
    • Is a low water plane to which soundings are reduced and above which drying heights are given in the rendered digital data set, on the fair sheet and in other survey records.
    • This datum is employed in the field.
  10. Chart Datum
    • Is the level to which soundings are reduced on the published chart and to which tidal heights are referred to in ANTT.
    • It should be a plane so low that the tide will seldom fall below it.
    • CD's may differ to SD's.

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