VERDAT

  1. mean low water springs: (MLWS) - the average height of the low waters of spring tides. Also called spring low water. (IHO Dictionary, S-32, 5th Edition, 3150)
  2. mean lower low water springs: (MLLWS) - the average height of lower low water springs at a place. (IHO Dictionary, S-32, 5th Edition, 3146)
  3. mean sea level: (MSL) - the average height of the surface of the sea at a tide station for all stages of the tide over a 19-year period, usually determined from hourly height readings measured from a fixed predetermined reference level. (IHO Dictionary, S-32, 5th Edition, 3156)
  4. lowest low water: an arbitrary level conforming to the lowest tide observed at a place, or some what lower.
  5. mean low water: (MLW) - the average height of all low waters at a place over a 19-year period. (IHO Dictionary, S-32, 5th Edition, 3147)
  6. 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. (Hydrographic Service, Royal Australian Navy)
  7. approximate mean low water springs: an arbitrary level, usually within ± 0.3m from that of mean low water springs (MLWS). (Hydrographic Service, Royal Australian Navy)
  8. Indian spring low water: (ISLW) - an arbitrary tidal datum approximating the level of the mean of the lower low water at spring tides. Also called Indian tidal plane. (IHO Dictionary, S-32, 5th Edition, 2427)

    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. Also called Indian tide plane. (Hydrographic Service, Royal Australian Navy).

  9. low water springs: an arbitrary level, approximating that of mean low water springs (MLWS). (Hydrographic Service, Royal Australian Navy)
  10. approximate lowest astronomical tide: an arbitrary level, usually within ± 0.3m from that of lowest astronomical tide (LAT). (Hydrographic Service, Royal Australian Navy)
  11. nearly lowest low water: an arbitrary level approximating the lowest water level observed at a place, usually equivalent to the Indian spring low water (ISLW). (Hydrographic Service, Royal Australian Navy)
  12. mean lower low water: (MLLW) - the average height of the lower low waters at a place over a 19-year period. (IHO Dictionary, S-32, 5th Edition, 3145)
  13. low water: an approximation of mean low water adopted as the reference level for a limited area, irrespective of better determinations at a later date. Used mostly in harbour and river engineering.

    14. used in inland (non-tidal) waters. It is generally defined as a level which the daily mean water level would fall below less than 5% of the time and by no more than 0.2 metres during the navigation season. A single level surface is usually chosen as the low water datum for a whole lake. On a river, low water datum is a sloping surface which approximates the river surface at a low state. (Canadian Hydrographic Service)

  14. approximate mean low water: an arbitrary level, usually within ± 0.3m from that of mean low water (MLW). (Hydrographic Service, Royal Australian Navy)
  15. approximate mean lower low water: an arbitrary level, usually within ± 0.3m from that of mean lower low water (MLLW). (Hydrographic Service, Royal Australian Navy)
  16. mean high water: (MHW) - the average height of all high waters at a place over a 19-year period. (IHO Dictionary, S-32, 5th Edition, 3141)
  17. mean high water springs: (MHWS) - the average height of the high waters of spring tides. Also called spring high water. (IHO Dictionary, S-32, 5th Edition, 3144)
  18. high water: the highest level reached at a place by the water surface in one tidal cycle. Also called high tide. (IHO Dictionary, S-32, 5th Edition, 2251)

    when used on inland (non-tidal) waters it is generally defined as a level which the daily mean water level exceeds less than 5% of the time.

  19. approximate mean sea level: an arbitrary level, usually within ± 0.3m from that of mean sea level (MSL). (Hydrographic Service, Royal Australian Navy)
  20. high water springs: an arbitrary level, approximating that of mean high water springs (MHWS). (Hydrographic Service, Royal Australian Navy)
  21. mean higher high water: (MHHW) - the average height of higher high waters at a place over a 19-year period. (IHO Dictionary, S-32, 5th Edition, 3140)
  22. equinoctial spring low water: the level of low water springs near the time of an equinox.
  23. lowest astronomical tide: (LAT) - the lowest tide level which can be predicted to occur under average meterological conditions and under any combination of astronomical conditions. (IHO Dictionary, S-32, 5th Edition, 2936)
  24. local datum: an arbitrary datum defined by a local harbour authority, from which levels and tidal heights are measured by this authority.
  25. international great lakes datum 1985: (IGLD 1985) - a vertical reference system with its zero based on the mean water level at Rimouski/Pointe-au-Père, Quebec, over the period 1970 to 1988.
  26. mean water level: the average of all hourly water levels over the available period of record.
  27. lower low water large tide: (LLWLT) - the average of the lowest low waters, one from each of 19 years of observations.
  28. higher high water large tide: (HHWLT) - the average of the highest high waters, one from each of 19 years of observations.
  29. nearly highest high water: an arbitrary level approximating the highest water level observed at a place, usually equivalent to the high water springs.
  30. highest astronomical tide (HAT): the highest tidal level which can be predicted to occur under average meteorological conditions and under any combination of astronomical conditions (IHO Dictionary, S-32, 5th Edition, 2244)