Assessment of tidal range changes in the North Sea from 1958 to 2014

The impact of baroclinity on tidal ranges in the North Sea

10.5194/egusphere-egu2020-19147 ◽

2020 ◽

Author(s):

Wenguo Li ◽

Bernhard Mayer ◽

Thomas Pohlmann

Keyword(s):

Sea Level ◽

North Sea ◽

Tide Gauge ◽

Tidal Range ◽

Baroclinic Mode ◽

Kelvin Wave ◽

Ocean Stratification ◽

The North ◽

The North Sea ◽

The Impact

Tidal range is one of significant contributors of coastal inundation. Therefore, it is very important to investigate the dynamics of tidal range variations over different time scales. The baroclinity has the potential to modulate surface tides through ocean stratification on seasonal scale. In order to better understand the impact of ocean stratification on tidal ranges in the North Sea, the numerical simulations were carried out in baroclinic and barotropic modes covering the period from 1948 to 2014, using the regional 3D hydrodynamic prognostic Hamburg Shelf Ocean Model (HAMSOM). In the barotropic mode, the river forcing was also included, which only increases the local sea level without any influence on the density. The tidal range difference between baroclinic and barotropic modes in winter (less stratification) and summer (strong stratification) are compared at 22 tide-gauge stations, where the simulated sea surface elevations agree well with observations from 1950 to 2014. The statistical analysis generally shows that the difference at 19 stations (86% of total stations) in summer is much larger than that in winter during more than 32 years (50% of the analysis period). This suggests that the stratification decouples the surface and bottom layers weakening the damping effects of bottom friction, which is visible even at the coastal tide-gauge stations, where the ocean water is well-mixed. Obviously, the signal induced by stratification is propagated by the tidal Kelvin wave through the North Sea. Additionally, the spatial distribution of tidal range differences indicate that the amphidromic points in the North Sea moved westward in the baroclinic mode. Regarding the seasonal mean sea level at the stations, the results show that the coastal sea level could be increased by baroclinity itself, since the river runoff freshens the coastal water in the baroclinic mode, and thus the local sea level increases due to steric effect. Consequently, the increased sea level could further weaken the damping effect. However, this is a relatively minor impact on the tidal range.

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Assessing 20th century tidal range changes in the North Sea

10.1002/essoar.10503227.1 ◽

2020 ◽

Author(s):

Leon Jänicke ◽

Andra Ebener ◽

Sönke Dangendorf ◽

Arne Arns ◽

Michael Schindelegger ◽

...

Keyword(s):

20Th Century ◽

North Sea ◽

Tidal Range ◽

The North ◽

The North Sea

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Assessment of tidal range changes in the North Sea from 1958 to 2014

10.5194/egusphere-egu21-14706 ◽

2021 ◽

Author(s):

Leon Jänicke ◽

Andra Ebener ◽

Sönke Dangendorf ◽

Arne Arns ◽

Michael Schindelegger ◽

...

Keyword(s):

North Sea ◽

German Bight ◽

Large Scale ◽

Tide Gauge ◽

Tidal Range ◽

Tide Gauges ◽

Tide Gauge Records ◽

Large Spatial Scale ◽

The North ◽

The North Sea

Tide gauges throughout the North Sea basin show significant changes in the local tidal regime since the mid-20th century, especially in the German Bight area. These changes were analyzed within the DFG-funded project TIDEDYN (Analyzing long term changes in the tidal dynamics of the North Sea, project number 290112166) and the final results were recently published in J&#228;nicke et al. (2020, https://doi.org/10.1029/2020JC016456).In this paper, we document an exceptional large-spatial scale case of changes in tidal range in the North Sea, featuring pronounced trends between -2.3 mm/yr at tide gauges in the UK and up to 7 mm/yr in the German Bight between 1958 and 2014. These changes are spatially heterogeneous and driven by a superposition of local and large-scale processes within the basin. We use principal component analysis to separate large-scale signals appearing coherently over multiple stations from rather localized changes. We identify two leading principal components (PCs) that explain about 69% of tidal range changes in the entire North Sea including the divergent trend pattern along UK and German coastlines that reflects movement of the region&#8217;s semidiurnal amphidromic areas. By applying numerical and statistical analyses, we can assign a baroclinic (PC1) and a barotropic large-scale signal (PC2), explaining a large part of the overall variance. A comparison between PC2 and tide gauge records along the European Atlantic coast, Iceland and Canada shows significant correlations on time scales of less than 2 years, which points to an external and basin-wide forcing mechanism. By contrast, PC1 dominates in the southern North Sea and originates, at least in part, from stratification changes in nearby shallow waters. In particular, from an analysis of observed density profiles, we suggest that an increased strength and duration of the summer pycnocline has stabilized the water column against turbulent dissipation and allowed for higher tidal elevations at the coast.We would like to present these research results and the content of the paper (cf. J&#228;nicke et al., 2020) at vEGU21, hoping to encourage subsequent questions and further discussions.

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ADJUSTMENT AND VERIFICATION OF THE RANDDELTA II MODEL

Coastal Engineering Proceedings ◽

10.9753/icce.v16.61 ◽

1978 ◽

Vol 1 (16) ◽

pp. 61

Author(s):

A. Langerak ◽

M.A.M. De Ras ◽

J.J. Leendertse

Keyword(s):

The Netherlands ◽

North Sea ◽

Sand Dunes ◽

Storm Surges ◽

Water Levels ◽

Tidal Marshes ◽

Tidal Range ◽

Offshore Area ◽

The North ◽

The North Sea

In the mid-1950s the Netherlands government embarked on a massive construction program, called the Delta Plan. Its purpose was to enhance protection from floods caused by the North Sea in the estuaries of the Rhine, Meuse and Scheldt. According to the plan, all connections to the sea were to be closed by dams, except the New Waterway to Rotterdam and the Western Scheldt. In 1974 all dams and dikes were complete except the dam closing off the Eastern Scheldt from the sea. In view of growing opposition to a complete closure, plans were revised in 1976, and instead of the dam, a storm surge barrier will be constructed. This barrier will reduce the tidal range in the Eastern Scheldt and will be closed during storm surges. In support of engineering and environmental studies related to the construction and operation of this barrier, a large numerical model has been developed, which covers the Eastern and Western Scheldt and the adjacent offshore area. The section of the North Sea which is included in the model is about 120 km long and 30 km wide, running from Blankenberghe in Belgium to Scheveningen in the Netherlands (Fig. 1). The bathymetry of the model area varies widely. In general it slopes from the shore to about 25 m at 30 km from the coast. In certain sections of the offshore area, the bottom is relatively flat; in other areas it has offshore bars and the bottom contains underwater sand dunes with a height of several meters. In the estuaries the tidal flow has scoured deep channels. The tidal flats near the North Sea are generally sandy, but the ecologically important tidal marshes located more inland contain much finer material. The flow and the water levels in the region which is modeled are generally tide-induced. However, the influence of meteorological effects is always present and sometimes dominates water movements and water levels (storm surges). The influence of the fresh water discharges is of much less importance; generally their effects can only be noticed in the immediate vicinity of the discharge. The tides in the offshore area of the model are part of the complicated tide system in the North Sea. The semidiurnal tidal wave propagates along the coast in a northeasterly direction. During this propagation the amplitude reduces from about 1.90 m near Blankenberghe to about .85 m near Scheveningen.

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WAVE CLIMATE STUDY In THE REGION OF THE EAST FRISIAN ISLANDS AND COAST

Coastal Engineering Proceedings ◽

10.9753/icce.v16.6 ◽

1978 ◽

Vol 1 (16) ◽

pp. 6

Author(s):

Hanz Dieter Niemeyer

Keyword(s):

North Sea ◽

Wave Climate ◽

Tidal Range ◽

Wide Spread ◽

Tidal Inlets ◽

The North ◽

The North Sea ◽

Southern Border ◽

A Chain ◽

Climate Study

The East Frisian Islands and Coast - located at the southern border of the North-Sea - are significantly characterized by a chain of off-shore islands which are separated from the mainland by wide spread tidal flats (FIG.1). Between the islands there are small and deep tidal inlets with strong currents, through which the tidal volume covering the flats is streaming in and out, with a tidal range of about 2,5 m.

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