Project Details
Projekt
Analysis of long-term changes in the tidal dynamics of the North Sea
Subject Area
Oceanography
Term
from 2016 to 2022
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 290112166
Historical tide gauge observations from the southeastern North Sea exhibit significant long-term changes in the local tidal regime during the 2nd half of the 20th century. While mean sea level (MSL) changes since 1900 have generally followed the global mean (in terms of the long-term trend), tidal low and high water levels are marked by distinct differences. For instance, the tidal high water levels have risen significantly faster than MSL, while the tidal lows are characterized by significantly smaller or even negative trends. This divergent development resulted in an increase of roughly 10 % in the mean tidal range since 1955. Such changes have a direct impact on coastal protection. For example, rising high water levels are accompanied by larger water depths leading to considerable changes in the local wave climate, in particular in areas of coastal mudflats and barrier islands of the German Bight. Additionally, larger wave heights and increased orbital velocities leading to extensive erosions can be expected, while decreases in the tidal low water levels have a serious impact on the navigability of coastal and estuarine regions. The increased tidal ranges (the difference between tidal high and low water levels) further involve larger tidal stream velocities, which exacerbate morphological changes in tidal channels, island erosion, beach erosion, and in case of storm surges abrasion of coastal dunes or cliff retreat. Therefore, it is clear that despite the globally appearing changes in MSL due to ice melting and thermal expansion, there are also regional phenomena and processes, which affect the local water levels. An improved understanding of all underlying processes is indispensible to derive reliable projections of future regional sea level changes. The main goal of TIDEDYN is therefore to analyze past changes in the local tidal regime in the North Sea. The observed increase in the mean tidal range is worldwide unique in its shape and the causes remain unexplained till today. Possible explanations are the increase in MSL, morphological changes in near coastal areas (which can be either natural or anthropogenic (e.g. dredging works, or building measures such as embankments) in nature), or seasonal changes in the thermohaline stratification of the ocean. By applying an integrated analysis of barotropic and baroclinic numerical high resolution models in combination with robust approaches of time series analyses we aim to systematically characterize, model, and explain the observed changes in the local tidal regime of the North Sea over the past 60 to 70 years. Numerical sensitivity studies will be used to separate different processes from each other.
DFG Programme
Research Grants
International Connection
Norway, United Kingdom
Cooperation Partners
Dr. Ivan David Haigh, Ph.D.; Professor Dr. Malte Müller
