Tidal Characteristic Numbers of Salinity: Difference between revisions

Revision as of 13:03, 11 June 2010

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.

Definitions for the Tidal Characteristic Numbers of Salinity

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

Ebb Current

Advective Ebb Transport of Salt

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

Example: Advective Ebb Transport of Salt in the Inner Außenweser

Tidal Cycle

Maximum Salinity

maximum value of salinity during a complete tidal cycle (period between two subsequent slack water times of ebb current)

Example: Maximum Salinity in the Inner Außenweser

Minimum Salinity

minimum value of salinity during a complete tidal cycle (period between two subsequent slack water times of ebb current)

Example: Minimum Salinity in the Inner Außenweser

Mean Salinity

average value of salinity during a complete tidal cycle (period between two subsequent slack water times of ebb current)

Example: Mean Salinity in the Inner Außenweser

Tidal Variation of Salinity

difference between the extreme values of salinity during a complete tidal cycle (period between two subsequent slack water times of ebb current)

Example: Tidal Variation of Salinity in the Inner Außenweser

Advective Residual Transport of Salt

residual salt volume which is transported by means of ebb and flood currents through a cross section (the different transport directions are taken into account). If the advective transport by means of flood current is equal but in opposite direction of the ebb current transport this will result in a zero advective residual transport of salt.

Example: Advective Residual Transport of Salt in the Inner Außenweser

Advective Salt Transport, Flood-Ebb-Ratio

flood to ebb ratio for the salt volumes which are transported by means of flood and ebb currents

Example: Flood-Ebb-Ratio for the Advective Salt Transport in the Inner Außenweser

back to Analysis of Calculated Results

Overview

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 ==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 [[Example: Animation of Tidal Variability of Salinity|animation of tidal variability of salinity]] in the Außenweser Estuary).
+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).