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Characteristic Numbers of Water Level (independent of tides)

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Revision as of 12:22, 10 October 2017 by imported>Lang Guenther (Low Water Level (LW): minimum valid water level added)
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Graphical representation of tide independent characteristic numbers of water level (with German text only).
This graphical representation is also available in Encapsulated PostScript format.

Motivation

Calculation and graphic display of several tide-independent characteristic numbers of water level can yield additional insight into the behaviour of natural coastal and/or inland waters. In contrast to the computation of the tidal characteristic numbers of water level the tide-independent numbers can be preferable used for

  • natural waters which are not dominated by the tides, e.g. like the coastal waters and estuaries along the Baltic Sea coast of Germany, or in
  • extreme situations, like for example during storm surge conditions in estuaries along the North Sea coast, when the water level deviates strongly from the average (tide-dominated) conditions, as well as for the
  • determination of characteristic water levels (e.g. HW and LW) for an arbitrary long (or short) period of time.

In particular there are several useful applications possible for this type of data analysis:

  • In addition to informations about the highest and lowest water levels which occur during an arbitrary period on can calculate also the water level difference for this time span. This is a good indicator for the maximum natural water level variability.
  • The time-dependent evolution of a high water event (flood event) or a low water event is reflected in the results for the times of high water and low water respectively.
  • Maximum velocities for the rise and the fall of the water surface are an additional measure for the characterization of e.g. storm surges.
  • From the computed times for the duration of high water and the duration of low water one can draw conclusions with respect to the loading of dikes which can result in possible damage.
  • The variance of the time-dependent water level evolution with respect to the mean water level can be used as an indicator for the dynamics of a natural water system.

An automatic analysis of all tide-independent characteristic numbers of water level is carried through by the computer programs LZKWF and NCANALYSE.

Definitions for the tide-independent characteristic numbers of water level

High Water Level (HW)

Highest water level within an arbitrary period of time. Invald data are only allowed to result from drying (no water).
Example figures: High water level.
Data analysis: LZKWF and NCANALYSE.

Maximum valid Water Level (xWL)

Highest valid water level within an arbitrary period of time, computed out of a time serie which may contain invalid data due to different reasons (drying, instrument failure, etc.).
Data analysis: NCANALYSE.

Low Water Level (LW)

Lowest water level within an arbitrary period of time. Invald data are only allowed to result from drying (no water).
Example figures: Low water level.
Data analysis: LZKWF and NCANALYSE.

Minimum valid Water Level (nWL)

Lowest valid water level within an arbitrary period of time, computed out of a time serie which may contain invalid data due to different reasons (drying, instrument failure, etc.).
Data analysis: NCANALYSE.

Mean Water Level (MW)

Arithmetic mean of the water level for an arbitrary period of time.
Computed for permanently flooded areas only.
Example figures: Mean water level.
Data analysis: LZKWF and NCANALYSE.

Water Level Difference (HW-LW)

Difference in height between HW and LW for an arbitrary period of time.
Computed for permanently flooded areas only.
Example figures: Water level difference.
Data analysis: LZKWF and NCANALYSE.

High Water Time

Official time of high water occurrence.
Example figures: High water time.
Data analysis: LZKWF and NCANALYSE.

Low Water Time

Official time of low water occurrence.
Example figures: Low water time.
Data analysis: LZKWF and NCANALYSE.

Duration of Inundation

Period of time during which an area is covered by water.
Example figures: Duration of inundation.
Data analysis: LZKWF and NCANALYSE.

Duration of Dry Period

Period of time during which an area is not covered by water.
Example figures: Duration of dry period.
Data analysis: LZKWF and NCANALYSE.

Maximum Rise Velocity

Maximum rise velocity of the water surface within an arbitrary period of time.
Example: Maximum Rise Velocity in the Ems Estuary.
Data analysis: LZKWF.

Maximum Fall Velocity

Maximum fall velocity of the water surface within an arbitrary period of time.
Example: Maximum Fall Velocity in the Ems Estuary.
Data analysis: LZKWF.

Standard Deviation of Water Level

Standard deviation of the water level elevation with respect to the mean water level within an arbitrary period of time.
Computed for permanently flooded areas only.
Example figures: Standard deviation of water level.
Data analysis: LZKWF and NCANALYSE.

Variance of Water Level

Variance of the water level elevation with respect to the mean water level within an arbitrary period of time.
Computed for permanently flooded areas only.
Example figures: Variance of water level.
Data analysis: LZKWF and NCANALYSE.

Duration of High Water

Time span for which the water level lies above a certain threshold within an arbitrary period of time.
Example figures: Duration of high water.
Data analysis: LZKWF and NCANALYSE.

Duration of Low Water

Time span for which the water level lies below a certain threshold within an arbitrary period of time.
Example figures: Duration of low water.
Data analysis: LZKWF and NCANALYSE.

Frequency Distribution of Water Level

Relative frequency for which the water levels are within an interval.
Example figures: Frequency distribution of water level.
Data analysis: NCANALYSE.

Cumulative Frequency Distribution of Water Level

Cumulative frequency with which the water levels are within an interval.
Example figures: Cumulative frequency distribution of water level.
Data analysis: NCANALYSE.

Frequency for the Exceedance of Water Level

Relative frequency for which the water levels are above a specific threshold.
Example figures: Frequency for the exceedance of water level threshold values.
Data analysis: NCANALYSE.

Frequency for the Underflow of Water Level

Relative frequency for which the water levels are below a specific threshold.
Example figures: Frequency for the underflow of water level threshold values.
Data analysis: NCANALYSE.

Quantiles of Water Level

Water level for a time serie which is not exceeded by a certain percentage of present water level values.
Computed for permanently flooded areas only.

Data analysis: NCANALYSE.



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