Tidal Characteristic Numbers of Salinity

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

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

Motivation

The calculation as well as the graphic visualization of various tidal characteristic numbers of salinity and also for the advective transport of salt contributes to an improved understanding of tidally dominated transport processes in estuaries. Spatial variations of salinity, advective transport of salt by means of flood and ebb currents can be highlighted for areas like coastal seas and estuaries as well (see also animation of tidal variability of salinity in the Außenweser Estuary).

• As the calculations are performed separately for the durations of ebb- and flood-current it can be shown that transport paths can differ significantly for the two tidal phases. From this one can get additional insight with respect to the relevant transport mechanisms dominated by the tidal currents. This can be related to locally varying flood-ebb asymmetries for ebb volume and flood volume. Also the presence of horizontal gradients can contribute to this effect.
• The variation of salinity resulting from the local maximum as well as the local minimum of salinity can be quite large. This is a consequence of fresh water inflow into an estuary. The value for the local salinity variation is mainly the result of the product between the horizontal salinity gradient and the lagrangian drift of a water particle during a complete tidal cycle. Due to the fact that salt is mainly advectively transported by means of the tidal current. The water particles which are passing at a location during a complete tidal cycle do have different regions of origin. Therefore they can also show substantial differences in salinity because estuaries are regions where fresh and sea water is mixed. For organisms which are living at the seabed and which cannot move the tidal variation of salinity is one of the significant natural stress factors (variation of the osmotic pressure due to salinity variations).

An automatic analysis of all tidal characteristic numbers of salinity is carried through by the computer program TDKSF.

=Flood Current

Advective Flood Transport of Salt

salt volume, which is transported by means of flood current through a cross section

Example: Advective Flood Transport of Salt in the Inner Außenweser

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Overview