Tidal Characteristic Numbers of Current
From BAWiki
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 programs TDKVF and NCANALYSE.
Definition of Tidal Characteristic Numbers of Current
Flood Current
Slack Water Time of Flood Current
Time of occurrence for slack water at the end of the flood relative to a reference position.
Example figures: slack water time of flood current.
Data analysis: TDKVF and NCANALYSE.
Slack Water Duration around Slack Water Time of Flood Current
Timespan around slack water time of flood current for which the flow velocity does not exceed a certain value (e.g. 0.2 m/s).
Example figures: slack water duration around slack water time of flood current.
Data analysis: TDKVF and NCANALYSE.
Slack Water Dislocation of Flood Current
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
Timespan between ebb slack and subsequent flood slack.
Example figures: flood current duration.
Data analysis: TDKVF and NCANALYSE.
Maximum Flood Current Velocity
Maximum value of current velocity during flood current duration.
Example figures: maximum flood current velocity.
Data analysis: TDKVF and NCANALYSE.
Mean Flood Current Velocity
Mean value of flood current velocity (computed from magnitude) during flood current duration.
Example figures: mean flood current velocity.
Data analysis: TDKVF and NCANALYSE.
Residual Flood Current Velocity
Residual flood current velocity (computed from addition of vectors).
Example figures: residual flood current velocity.
Data analysis: NCANALYSE.
Eulerian Flood Path
Vectorial sum of the path lengths for a certain location during flood current.
Example figures: eulerian flood path.
Data analysis: TDKVF and NCANALYSE.
Flood Volume
Volume of water which flows through a certain cross section during flood current.
Example: Flood Volume for the Inner Außenweser. Figure obsolete.
Data analysis: TDKVF. Not yet supported by NCANALYSE.
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. Figure obsolete.
Data analysis: TDKVF. No more supported by NCANALYSE.
Ebb Current
Slack Water Time of Ebb Current
Time of occurrence for slack water at the end of the ebb relative to a reference position.
Example figures: slack water time of ebb current.
Data analysis: TDKVF and NCANALYSE.
Slack Water Duration around Slack Water Time of Ebb Current
Timespan around slack water time of ebb current for which the flow velocity does not exceed a certain value (e.g. 0.2 m/s).
Example figures: slack water duration around slack water time of ebb current.
Data analysis: TDKVF and NCANALYSE.
Slack Water Dislocation of Ebb Current
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
Timespan between flood slack and subsequent ebb slack.
Example figures: ebb current duration.
Data analysis: TDKVF and NCANALYSE.
Maximum Ebb Current Velocity
Maximum value of current velocity during ebb current duration.
Example figures: maximum ebb current velocity.
Data analysis: TDKVF and NCANALYSE.
Mean Ebb Current Velocity
Mean value of ebb current velocity (computed from magnitude) during ebb current duration.
Example figures: mean ebb current velocity.
Data analysis: TDKVF and NCANALYSE.
Residual Ebb Current Velocity
Residual ebb current velocity (computed from addition of vectors).
Example figures: residual ebb current velocity.
Data analysis: NCANALYSE.
Eulerian Ebb Path
Vectorial sum of the path lengths for a certain location during ebb current.
Example figures: eulerian ebb path.
Data analysis: TDKVF and NCANALYSE.
Ebb Volume
Volume of water which flows through a certain cross section during ebb current.
Example: Ebb Volume for the Inner Außenweser. Figure obsolete.
Data analysis: TDKVF. Not yet supported by NCANALYSE.
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. Figure obsolete.
Data analysis: TDKVF. No more supported by NCANALYSE.
Tidal Cycle
Tide Current Duration
Tide current duration.
Example figures: tide current duration.
Data analysis: NCANALYSE.
Flood Current Duration : Ebb Current Duration
Ratio of flood current duration to ebb current duration.
Example figures: flood current duration : ebb current duration.
Data analysis: TDKVF and NCANALYSE.
Flood Current Duration : Tide Current Duration
Ratio of flood current duration to tide current duration.
Example figures: flood current duration : tide current duration.
Data analysis: NCANALYSE.
Ebb Current Duration : Tide Current Duration
Ratio of ebb current duration to tide current duration.
Example figures: ebb current duration : tide current duration.
Data analysis: NCANALYSE.
Mean Tide Current Velocity
Mean value of the current velocity during a tidal cycle (from ebb slack to ebb slack).
Example figures: mean tide current velocity.
Data analysis: NCANALYSE.
Max. Flood Current Velocity : Max. Ebb Current Velocity
Ratio of maximum flood current velocity to maximum ebb current velocity.
Example figures: maximum flood current : maximum ebb current.
Data analysis: TDKVF and NCANALYSE.
Maximum Flood Current Velocity : Mean Tide Current Velocity
Ratio of maximum flood current velocity to mean tide current velocity.
Example figures: maximum flood current : mean tide current.
Data analysis: NCANALYSE.
Maximum Ebb Current Velocity : Mean Tide Current Velocity
Ratio of maximum ebb current velocity to mean tide current velocity.
Example figures: maximum ebb current : mean tide current.
Data analysis: NCANALYSE.
Mean Flood Current Velocity : Mean Ebb Current Velocity
Ratio of mean flood current velocity to mean ebb current velocity.
Example figures: mean flood current : mean ebb current.
Data analysis: TDKVF and NCANALYSE.
Mean Flood Current Velocity : Mean Tide Current Velocity
Ratio of mean flood current velocity to mean tide current velocity.
Example figures: mean flood current : mean tide current.
Data analysis: NCANALYSE.
Mean Ebb Current Velocity : Mean Tide Current Velocity
Ratio of mean ebb current velocity to mean tide current velocity.
Example figures: mean ebb current : mean tide current.
Data analysis: NCANALYSE.
Residual Current
Vectorial summation of the flow velocities for a certain location for a whole tidal period.
Example figures: residual current.
Data analysis: TDKVF and NCANALYSE.
Eulerian Flood Path : Eulerian Ebb Path
Ratio of the flood path to the ebb path.
Example figures: eulerian flood path : eulerian ebb path.
Data analysis: TDKVF and NCANALYSE.
Residual Path
Vectorial summation of the transport paths for a certain location for a whole tidal period.
Example figures: residual path.
Data analysis: TDKVF and NCANALYSE.
Tide Volume
Sum of the modules of the ebb volume and the flood volume.
Example: Tide Volume for the Inner Außenweser.
Data analysis: TDKVF.
Flood Volume : Ebb Volume
Ratio of the flood volume to the ebb volume.
Example: Ratio Flood Volume : Ebb Volume for the Inner Außenweser.
Data analysis: TDKVF.
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.
Data analysis: TDKVF.
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