Hydrological conditions
Water depth
According to the topographic chart of the seabed from soundings taken by the German FederalMaritime and Hydrographic Agency in 1991 the water depth at the site is approximately 23 m. A seismic research trip by the FS Alkor in May 2006 confirmed these soundings in principle, but registered depths that were generally about one meter less.
During the site investigation a water level of 22.2 m was measured, which according to tidal adjustment by the German FederalMaritime and Hydrographic Agency, produces a lowest astronomical tide (LAT) of 21.8 m.
Water level
The lowest astronomical tide (LAT – equivalent to the newer marine chart zero) was estimated from the coastal levels and assumed to be 0.2 m below low tide. According to information provided by the German Federal Maritime and Hydrographic Agency, the height of the highest astronomical tide (HAT) extrapolated from North Friesian levels is 2 m above low tide. Storm surge of 2.6 m should be included in the reckoning according to model calculations from the MUSE project of the German Federal Maritime and Hydrographic Agency.
This results in a theoretically possible maximum water level of 4.6 m above low tide or a maximum water depth of 26.6 m.
The design water level need not however be configured at the most unfavourable case of a very improbable coincidence of a maximum storm surge and the highest astronomical tide (together with the design wave). The maximum tide is therefore reduced by 0.3 m for this water level.
Water level | at LAT | absolute |
LAT - marine chart zero | 0 m | 21.8 m |
low tide | +0.2 m | 22 m |
high tide | +1.2 m | 23 m |
HAT | +2.2 m | 24 m |
storm surge | +2.6 m | max 26.6 m |
still water level | +4.5 m | 26.3 m |
Waves
Design waves
At SWL (26.3 m) the wave crest reaches heights of up to 14 m (40.3 m above ground or 18.5 m above marine chart zero).
The parameters of the design wave and of the 30- and 10-year high were set as follows:
parameters | 50 years | 30 years | 10 years | |
design water depth | d | 26.3 m | 26.3 m | 26.3 m |
designated wave height | H1/3 | 9.2 m | 8.9 m | 8.3 m |
designated wave height | Hmax | 17.9 m | 17.3 m | 16.2 m |
wave crest above marine chart zero | HSWL+η | 18.0 m | 17.7 m | 16.4 m |
wave lengths | l | 170 - 232 m | 166 - 224 m | 158 - 216 m |
wave periods | TD | 10.7 - 13.9 s | 10.6 - 13.6 s | 10.2 - 13.1 s |
Wave heading
This is based on statistical records of the WaveRider wave buoy NSBII of the German Federal Maritime and Hydrographic Agency from the years 1993-2006.
According to these records the main heading of the waves is west-southwest, the extreme events however generally occur with west to north-westerly directions as here the fetch is particularly great. Here, figures coming very close to the aforementioned 50-year figures for significant wave height were achieved in just 13 years.