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4. PERIODICAL SEA LEVEL OSCILLATIONS 
The German Baltic coast, situated on the western edge of the Baltic length axis, is 
predestined for relatively high storm surges, especially during northeasterly storms (Stigge, 
1994). Because of the economic relevance of the area, both a system of coastal protection 
and an operational water level forecasting service are needed. Coastal flood defences on the 
coasts (e.g. dykes) have been designed on the basis of local surge probabilities. The 
meteorological conditions causing a storm surge of about 1m on the Pomeranian coast may 
lead to a storm surge of about 1.5 m on the coast of Schleswig-Holstein. This has been taken 
into account in the historic development of coastal defences. Therefore, the dykes in the 
eastern parts are mostly lower than in the western parts of the German Baltic coast. Extreme 
sea level oscillations result not only from weather influences but also from seiches of the 
entire Baltic system (with periods of 27.5 - 39 hours) or from oscillations of bights or 
estuaries having characteristic periods of a few hours. Fig. 4.1. shows a water level 
oscillation of about 3 m per 24 hours at the tide gauge at Kiel-Holtenau. The oscillation was 
influenced by a change of wind direction from north-east to south-west in the Baltic Proper. 
Fig. 4.2. shows water level oscillations of about half a metre per hour in the Warnow estuary 
at Rostock. 
Kiel - Holtenau 
Tear 200 1 
Fig. 4.1. Water level oscillation of about 3 m in 24 hours at the tide gauge Kiel-Holtenau, 
influenced by a change of wind direction in the Baltic Proper. 
Especially the westernmost parts are influenced by regular tides having periods of 12.4 
hours and amplitudes of about 15 cm at Wismar (Fig. 4.3.), and 10 cm at Warnemunde. 
Therefore, storm surges with a duration of mostly about 1 or 2 days may be modified by 
different kinds of oscillation. 
Other periodic sea level changes that have been observed have periods of 1 1/2 years, with 
resulting elevations of about 20 cm. The mean sea level (of, e.g., one week) without any 
storm-induced elevation is a measure of the so-called ‘degree of filling' (of the whole Baltic 
sea). Sea levels rise when low pressure troughs travel across Scandinavia from south-west 
to north-east, and such situations may persist for several weeks. During such weather 
situations strong south-westerly winds occur in the Baltic Proper, westerly winds in the 
western Baltic, and north-westerly winds in the Kattegat. This leads to a permanent inflow of 
water masses from Kattegat to the western Baltic. Last but not least, also local winds may 
modify storm surges, as has been described by Stigge (1995).