Changes in sea level in the German Bight

Abstract

Tidal data recorded in the German Bight over the last 200yrshow that MHW (mean high water) has risen by about 20 to 30cm per century. Corresponding data on maximum flood levels over the last 400 yr show a similar increase of approximately 25 cm per century. At Cuxhaven, the graph of maximum annual water levels drawn from 150 yr of continuous recordings reveals a long term oscillation superimposed on the progressive linear increase in water levels. This oscillation has a period of roughly 80 yr and extrapolation suggests the next peak should occur around 1985.These rates of increase in sea level over recent centuries are compared against the perspective of much longer term trends.Preface (D. Prandle, Institute of Oceanographic Sciences, Bidston Observatory, Merseyside)

New Aspects Concerning the Increase of Sea Level on the German North Sea Coast

“…As already mentioned above and as described in previous papers, the records of most gauges on the German North Sea coast show an average rise of 25 cm per century since the beginning of the observations. Since about 1920, the curves of the 19 year overlapping means of MThw on several gauges became less steep (15) (16). In such cases where the decrease of the slope was less strong, effects of man-made influences are probable (e.g.…”

“…Figure 8 shows the curves of the 19 years overlapping means of MThw at Emden, Cuxhaven and Busum. The figure which was published already in (15) (16) has been expanded for the years up to 1983. Moreover the time-scale has been shifted in such a way that the mean values refer to the last year of the period respectively (e.g.…”

Frequency of Occurrence of Storm Surges in an Estuary: A Stochastic Approach

“…The variation of mean level, dealt with in this paragraph consists of periodic and secular changes, in which periodic means 'with a period of at least one year', thus excluding diurnal and shorter-period oscillations, classified as tidal effects. The variation in mean level, often substituted for by 'mean tidal level', is caused by mean sea level variations and by morphological changes of the river, due to the dynamic physical processes in the river and due to human interventions (35,40). The most important causes of mean sea level variation are : changes in the total water balance, movements in the land reference level (bench mark), time variations in the atmospheric forces (wind stress and air pressure), time variations in the oceanographic forces (temperature, salinity, currents) and finally long period astronomical tides.…”

“…The most important causes of mean sea level variation are : changes in the total water balance, movements in the land reference level (bench mark), time variations in the atmospheric forces (wind stress and air pressure), time variations in the oceanographic forces (temperature, salinity, currents) and finally long period astronomical tides. For a description of these phenomena reference is made to specific geophysical literature (24,35,37,39). With a view to obtain an homogeneous set of water level data along an estuary, one has to investigate not only mean sea level variations, but (depending upon the calculationprocedure to determine frequencies of occurrence) also trends in annual maxima and in tidal amplitude must be considered (see § 3.1.…”