Tidal Characteristic Numbers of Water Level

Graphical representation (available in -format, 28k) of characteristic numbers of water level (with German text only). This graphical representation is also available in Encapsulated PostScript format ( 29k).

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 the tidal range highlights the potential and kinetic energy which is related to the tidal wave. These three 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.
• 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 and ebb period, as well as the relationship between these two numbers give some information about the asymmetry or 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 program TDKWF.