Fourth Study Conference on BALTEX Scala Cinema Gudhjem

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Investigations of Variations in Water Level Times-Series at the German
Baltic Sea Coastline
Jürgen Jensen and Christoph Mudersbach
Research Centre for Water and Environmental Engineering (fwu) at University of Siegen, Paul-Bonatz-Str. 9-11,
57076 Siegen, Germany, phone +49-271-7402627, e-Mail: jensen@fb10.uni-siegen.de
1. Introduction
Changes in the global sea level have far reaching
consequences for both humans and the natural environment.
The whole German North Sea and Baltic Sea coastlines are
protected against storm surges by dykes in order to protect
the partially lower lying hinterland. Particularly in highly
industrialized countries, as, for example, Germany, space
requirements for population and industry are increasing. The
existing space is used intensively and, in the case of
flooding, high significant monetary and ecological damage
will result. As a result of strongly increasing shipping traffic,
shipping routes have been enlarged and are maintained. This
has a direct influence on the storm surges coming into the
estuaries, so that the inland can be affected more strongly by
the consequences of such a storm surge (e.g. Hamburg
1962).
The population and the economy must be protected against
flooding. To achieve this, knowledge of the long, medium
and short-term trends of the water levels is important.
The tidal range is about 3m at the North Sea coastline. At
the Baltic Sea no tidal range has to be considered.
2. Database
Data pre-processing is a very important and time-consuming
task. Data pre-processing is important because the original
data can contain discrepancies and mistakes. One must
check, therefore, whether there are obvious mistakes in the
time series, or in cases where the gauge datum has changed.
To make the data pre-processing and storage of data
effective, the development of a relational database system is
to be recommended. In this database, the data can be
managed in an easy way and simple analysis can be carried
out.
For the present investigation, a database system in MS
Access was developed (Fig. 1). This software was chosen
because it is universally available and special demands are
not made on the workstation.
3. Analysis and Results
In the present investigation, a statistical analysis of the time
series was carried out. Basic statistical parameters, such as,
for example, mean values and standard deviations, were
calculated for all time series. Four gauging stations at the
German Baltic Sea coastline were combined to so called
synthetic gauges to be able to make more general statements
about the variances in the Baltic Sea. Further analysis, such
as trends or adaptation functions, were carried out only for
the synthetic time series.
Figure 1. Initial form of the time series data base.
The statistical analyses of the time series were carried out
using the software package MATLAB (Version 6.5). With
the aid of different adaptation functions, statements about
the trends of the mean water levels at the German North
Sea and Baltic Sea coastline can be made up to the year
2020.
First, to all time series linear trends for different spans of
time were calculated. For a more detailed description of
the time series the influence of the nodal tide was
considered.
From this basis, further non-linear adaptation functions
were examined which can describe better the given time
series. The advantage of the nonlinear adaptation functions
lies in their ability to describe the available time series
more exactly. The disadvantage lies in the fact that they
cannot be used so well for extrapolation. Therefore,
particular care must be taken during the use of nonlinear
adaptation functions at the point when they are ”running
away”.
Some results are shown in figure 2, where the time series
of the Mean Sea Level (MSL) of the synthetic Baltic Sea
gauging station is fitted by several non-linear adaptation
functions.
In the further analysis, the question is interesting of how
the MSL of the North Sea and the Baltic Sea are related to
each other. Due to the small tidal range in the Baltic Sea,
the Baltic Sea can be considered as a damped gauge of the
North Sea. A correlation between the Baltic Sea ∆MMSL
and the ∆MMSL of the synthetic island-gauge North Sea
shows these relationships (Fig. 3).