Characteristic Numbers of Water Level (independent of tides)
From BAWiki
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 program LZKWF.
Definitions for the tide-independent characteristic numbers of water level
High Water Level (HW)
Highest water level within an arbitrary period of time.
Example: High Water Level in the Ems Estuary
Low Water Level (LW)
Lowest water level within an arbitrary period of time.
Example: Low water level in the Ems Estuary
Mean Water Level (MW)
Arithmetic mean of the water level for an arbitrary period of time.
Example: Mean Water Level in the Ems Estuary
Water Level Difference (HW-LW)
Difference in height between HW and LW for an arbitrary period of time.
Example: Water Level Difference in the Ems Estuary
High Water Time
Official time of high water occurrence.
Example: High water time in the Ems Estuary
Low Water Time
Official time of low water occurrence.
Example: Low Water Time in the Ems Estuary
Duration of Inundation
Period of time during which an area is covered by water.
Example: Duration of Inundation in the Ems Estuary
Duration of Dry Period
Period of time during which an area is not covered by water.
Example: Duration of Dry Period in the Ems Estuary
Maximum Rise Velocity
Maximum rise velocity of the water surface within an arbitrary period of time.
Example: Maximum Rise Velocity in the Ems Estuary
Maximum Fall Velocity
Maximum fall velocity of the water surface within an arbitrary period of time.
Example: Maximum Fall velocity in the Ems Estuary
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.
Example: Standard Deviation of Water Level in the Ems Estuary
Variance of Water Level
Variance of the water level elevation with respect to the mean water level within an arbitrary period of time.
Example: Variance of Water Level in the Ems Estuary
Duration of High Water
Time span for which the water level lies above a certain threshold within an arbitrary period of time.
Example: Duration of High Water in the Ems Estuary
Duration of Low Water
Time span for which the water level lies below a certain threshold within an arbitrary period of time.
Example: Duration of Low Water in the Ems Estuary
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