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Tidal Characteristic Numbers of Current

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Revision as of 13:35, 18 August 2014 by imported>Spohr Susanne

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

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

Graphical representation of eulerian residual current and residual path (with German text only). This graphical representation is also available in Encapsulated PostScript format.

Motivation

Computation as well as graphical display of several tidal characteristic numbers of current add aditional insight into tidally induced dynamic processes which are reflected in the current velocity and its related derived quantities. This type of tidal analysis should therefore go hand in hand with the calculation of tidal characteristic numbers of water level.

  • The computation is carried out separately for the periods of flood and ebb current duration. Therefore it yields information about the asymmetry of the tide-induced currents. An asymmetry can result in different durations of ebb and flood currents on the one hand side and on the other hand side in different maximum flood and ebb current velocities. This imbalance might be a result of different speeds for the fall and rise of the water level which causes a distinguished acceleration of the flow. Different values of the maximum flood and ebb current velocities may be a main cause for residual transport (up- or down-estuary) of bedload material or suspended sediments.
  • Unequal slack water times of flood or ebb current are mainly due to the varying significance of the various dynamic driving forces (e.g. batropic and baroclinic pressure gradient as well as bottom friction versus inertia forces). They mainly depend on water depth as well as on the precise location of the water volume in the water column.
  • Different times of slack water dislocation are related to the character of the tidal wave. In a purely propagating deep water wave there exists a phase shift of approximately 90 ° between current and water level elevation. Whereas in shallow water, bottom friction and reflexion of the tidal wave causes a much smaller phase shift. Remember: for a purely standing wave the phase shift is zero.
  • The periods of slack water are good indicators for the times of mild current climate. During these periods suspended sediments may settle to the bottom and become deposited. Unsymmetrical periods of slack water can result in net up- or down-estuary transport of suspended sediments.
  • Tidal characteristic numbers of current which are representative for the whole tidal cycle may give some insight into the residual transport paths for the water masses travelling along an estuary. For example the Eulerian residual current is a first order approximation to the respective Lagrangian one. It should be therefore interpreted with some care.

Automatic analyses for all of the above mentioned tidal characteristic numbers of current are carried out for 2D- as well as for 3D-data by the program TDKVF.

Definition of Tidal Characteristic Numbers of Current

Flood Current

Slack Water Time of Flood Current (Kf)

Official time of slack water occurrence at the end of a flood current duration.
Example figures: slack water time of flood current.
Data analysis: TDKVF and NCANALYSE.

Slack Water Duration around Slack Water Time of Flood Current (StwKf)

Timespan around slack water time of flood current for which the flow velocity does not exceed a certain value.
Example figures: slack water duration around slack water time of flood current.
Data analysis: TDKVF and NCANALYSE.

Slack Water Dislocation of Flood Current (KPVf)

Timespan between high water occurrence and slack water time of flood current.
Example figures: slack water dislocation of flood current.
Data analysis: TDKVF and NCANALYSE.

Flood Current Duration (FDau)

Timespan between slack water time of flood current and the next slack water time of ebb current.
Example figures: flood current duration.
Data analysis: TDKVF and NCANALYSE.

Flood Current Duration : Tide Current Duration (FTStD)

Ratio of the flood current duration to the tide current duration.
Example figures: flood current duration : tide current duration.
Data analysis: NCANALYSE.

Maximum Flood Current Velocity (Vfx)

Maximum value of the flood current velocity during the flood current duration.
Example figures: maximum flood current velocity.
Data analysis: TDKVF and NCANALYSE.

Maximum Flood Current Velocity : Mean Tide Current Velocity (VFxT)

Ratio of the maximum flood current velocity to the mean tide current velocity.
Example figures: maximum flood current : mean tide current.
Data analysis: NCANALYSE.

Mean Flood Current Velocity (Vfm)

Mean value of the flood current velocity during the flood current duration.
Example figures: maximum flood current velocity.
Data analysis: TDKVF and NCANALYSE.

Mean Flood Current Velocity : Mean Tide Current Velocity (VFmT)

Ratio of the mean flood current velocity to the mean tide current velocity.
Example figures: mean flood current : mean tide current.
Data analysis: NCANALYSE.

Residual Flood Current Velocity (VfRe)

residual flood current velocity.
Example figures: residual flood current velocity.
Data analysis: NCANALYSE.

Eulerian Flood Path (Wf)

Vectorial summation of the path length for a certain location during the flood current duration.
Example figures: eulerian flood path.
Data analysis: NCANALYSE.

Flood Volume

Volume of water, which flows through a certain cross section during the flood current duration.
Example: Flood Volume for the Inner Außenweser
Data analysis: TDKVF.

Differences of Time of Maximum Flood Current between Different Locations

Differences of time of maximum flood current occurrence between different locations within the area of data analysis.
Example: Time of Maximum Flood Current for the Inner Außenweser
Data analysis: TDKVF.


Ebb Current

Slack Water Time of Ebb Current (Ke)

Official time of slack water occurrence at the end of a ebb current duration.
Example figures: slack water time of ebb current.
Data analysis: TDKVF and NCANALYSE.

Slack Water Duration around Slack Water Time of Ebb Current (StwKe)

Timespan around slack water time of ebb current for which the flow velocity does not exceed a certain value.
Example figures: slack water duration around slack water time of ebb current.
Data analysis: TDKVF and NCANALYSE.

Slack Water Dislocation of Ebb Current (KPVe)

Timespan between high water occurrence and slack water time of ebb current.
Example figures: slack water dislocation of ebb current.
Data analysis: TDKVF and NCANALYSE.

Ebb Current Duration (EDau)

Timespan between slack water time of ebb current and the next slack water time of flood current.
Example figures: ebb current duration.
Data analysis: TDKVF and NCANALYSE.

Ebb Current Duration : Tide Current Duration (ETStD)

Ratio of the ebb current duration to the tide current duration.
Example figures: ebb current duration : tide current duration.
Data analysis: NCANALYSE.

Maximum Ebb Current Velocity (Vex)

Maximum value of the ebb current velocity during the ebb current duration.
Example figures: maximum ebb current velocity.
Data analysis: TDKVF and NCANALYSE.

Maximum Ebb Current Velocity : Mean Tide Current Velocity (VExT)

Ratio of the maximum ebb current velocity to the mean tide current velocity.
Example figures: maximum ebb current : mean tide current.
Data analysis: NCANALYSE.

Mean Ebb Current Velocity (Vem)

Mean value of the ebb current velocity during the flood current duration.
Example figures: mean ebb current velocity.
Data analysis: TDKVF and NCANALYSE.

Mean Ebb Current Velocity : Mean Tide Current Velocity (VEmT)

Ratio of the mean ebb current velocity to the mean tide current velocity.
Example figures: mean ebb current : mean tide current.
Data analysis: NCANALYSE.

Residual Ebb Current Velocity (VeRe)

residual ebb current velocity.
Example figures: residual ebb current velocity.
Data analysis: NCANALYSE.

Eulerian Ebb Path (We)

Vectorial summation of the path length for a certain location during the ebb current duration.
Example figures: eulerian ebb path.
Data analysis: TDKVF and NCANALYSE.

Ebb Volume

Volume of water, which flows through a certain cross section during the ebb current duration.
Example: Ebb Volume for the Inner Außenweser.
Data analysis: TDKVF.

Differences of Time of Maximum Ebb Current between Different Locations

Differences of time of maximum ebb current occurrence between different locations within the area of data analysis.
Example: Time of Maximum Ebb Current for the Inner Außenweser.
Data analysis: TDKVF.


Tidal Cycle

Residual Current

Vectorial summation of the flow velocities for a certain location for a whole tidal poriod

Example: Residual Current for the Inner Außenweser

Eulerian Residual Path

Vectorial summation of the transport paths for a certain location for a whole tidal poriod

Example: Eulerian Residual Path for the Inner Außenweser

Residual Flow

Residual volume of water, which flows through a certain cross section within a whole tidal poriod

Example: Residual Flow for the Inner Außenweser

Tide Volume

Sum of the modules of the ebb volume and the flood volume

Example: Tide Volume for the Inner Außenweser

Ratio Flood Current Duration : Ebb Current Duration

Ratio of flood current duration to ebb current duration

Example: Ratio Flood Current Duration : Ebb Current Duration for the Inner Außenweser

Ratio Max. Flood Current Velocity : Max. Ebb Current Velocity

Ratio of the maximum value of the flood current velocity to the maximum value of the ebb current velocity

Example: Ratio Max. Flood Current Velocity : Max. Ebb Current Velocity for the Inner Außenweser

Ratio Mean Flood Current Velocity : Mean Ebb Current Velocity

Ratio of the mean value of the flood current velocity to the mean value of the ebb current velocity

Example: Ratio Mean Flood Current Velocity : Mean Ebb Current Velocity for the Inner Außenweser

Ratio Flood Path : Ebb Path

Ratio of the flood path to the ebb path

Example: Ratio Flood Path : Ebb Path for the Inner Außenweser

Ratio Flood Volume : Ebb Volume

Ratio of the flood volume to the ebb volume

Example: Ratio Flood Volume : Ebb Volume for the Inner Außenweser


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