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Tidal Characteristic Numbers of Water Level

From BAWiki

Graphical representation of characteristic numbers of water level (with German text only). This graphical representation is also available in Encapsulated PostScript format.

Motivation

The calculation and graphic display of the tidal characteristic numbers of water level contributes to a large amount for an improved understanding of the tide induced dynamic processes in coastal seas and estuaries.

  • Calculating high water, low water as well as flood tide rise, ebb tide fall and tidal range highlight the potential and kinetic energy which is related to the tidal wave. These quantities are spatially varying in dependence on the ratio between dissipative processes (e.g. bottom friction) and (re-) enforcing ones (namely resonance in shallow channels or concentration of energy due to a converging coastline and bathymetry).
  • The mean tidal level does vary moderately compared to the the above mentioned quantities. Anyway, there exists a clear relationship to the fresh water inflow, the wind induced setup or nonlinear interactions of the tidal harmonic constituents.
  • Differences between mean flood water level and mean ebb water level give us some first information concerning asymmetry of the tidal wave, which is e.g. caused by the different shape of the tide during tidal rise and tidal fall.
  • The spatial variations of the high water time or the low water time gives a good impression of the speed of propagation of the crest and trough of a tidal wave within a study area. If the lines of equal time of high and/or low water are separated by large distances this indicates an apparently fast propagating wave, normally related to strong reflexion of the tide at boundaries. This speed of propagation should not be confused with the celerity of the tidal wave, which can be significantly smaller.
  • Flood period, ebb period and tide period, as well as the various relationships between these numbers give some information about the asymmetry of the tidal wave, which are reflected in the different periods for the rise and fall of the water level elevation. Asymmetries which are already visible in the tidal wave have a good chance to become much more pronounced in current velocity asymmetries; the latter ones result in e.g. tide induced suspended sediment transport processes.
  • Exact knowledge of the inundation period can be relevant to ecologists or hikers crossing tidal flats (from the coastline to a dry sandbank). Also for improved navigation - professional or for leisure - this is a really relevant information.

An automatic analysis of all tidal characteristic numbers of water level is carried through by the computer programs TDKWF and NCANALYSE.

Definition of the Tidal Characteristic Numbers of Water Level

High Water Level (HW)

Highest water level between two subsequent low waters.
Example figures: High water.
Data analysis: TDKWF and NCANALYSE.

Low Water Level (LW)

Lowest water level between two subsequent high waters.
Example figures: Low water.
Data analysis: TDKWF and NCANALYSE.

Tidal Range

Mean water level difference between high water and two neighbouring low waters.
Example figures: Tidal range.
Data analysis: TDKWF and NCANALYSE.

Mean Tide Level

Mean water level for a tidal cycle (between two subsequent low waters).
Example figures: Mean tide level.
Data analysis: TDKWF and NCANALYSE.

Mean Flood Water Level

Mean water level for the flood period (tide rise) of a tidal cycle.
Example figures: Mean flood water level.
Data analysis: NCANALYSE.

Mean Ebb Water Level

Mean water level for the ebb period (tide fall) of a tidal cycle.
Example figures: Mean ebb water level.
Data analysis: NCANALYSE.

Flood Period

Period from low water to the next high water.
Example figures: Flood period.
Data analysis: TDKWF and NCANALYSE.

Ebb Period

Period from high water to the low high water.
Example figures: Ebb period.
Data analysis: TDKWF and NCANALYSE.

Flood Period : Ebb Period

Ratio in flood period to ebb period.
Example figures: Flood period : ebb period.
Data analysis: TDKWF and NCANALYSE.

Tide Period

Time span between two successive LW of a tidal cycle.
Example figures: Tide period.
Data analysis: NCANALYSE.

Flood Period : Tide Period

Ratio in flood period to tide period.
Example figures: Flood period : tide period.
Data analysis: NCANALYSE.

Ebb Period : Tide Period

Ratio in ebb period to tide period.
Example figures: Ebb period : tide period.
Data analysis: NCANALYSE.

High Water Time (T_HW)

Official time of high water occurrence.
Data analysis: TDKWF and NCANALYSE. Example figures: High water time.

Low Water Time (T_LW)

Official time of low water occurrence.
Example figures: Low water time.
Data analysis: TDKWF and NCANALYSE.

Flood Tide Rise

Water level difference (rise) between the first LW and the HW of a tidal cycle.
Example figures: Flood tide rise.
Data analysis: NCANALYSE.

Ebb Tide Fall

Water level difference (fall) between the HW and the second LW of a tidal cycle.
Example figures: Ebb tide fall.
Data analysis: NCANALYSE.

Inundation Period

Period of time within a tidal cycle, during which an area is covered by water.
Example figures: Inundation period.
Data analysis: TDKWF and NCANALYSE.


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