How can the consequences of storms and rising water levels in the tidal river Elbe, resulting from climate change, be minimized? This is what the TU Institute of River and Coastal Engineering is investigating for several time frames up to 2200.
"Without flood protection, large parts of northern Germany would already be flooded today," is how Professor Peter Fröhle sums up the situation. This applies not only to the coast from Husum to Wilhelmshaven; high water levels and storms would also change the appearance of the landscape between Hamburg and Brunsbüttel. The areas along the tidal Elbe, which is characterized by high and low tides, would be almost impossible to settle without flood protection with dikes and protective walls. But estuaries like the Tidal Elbe were and are lifelines for the hinterland. Settlements, towns, companies and ports have grown up along these estuaries and in many cases have ensured prosperous economic development. These, as well as the valuable biotopes and ecosystems, must be protected and preserved in the future.
The effects of climate change on this area and which possible flood protection measures would make sense in the future are being discussed in the TideelbeKlima project at the Institute of Hydraulic Engineering at the Hamburg University of Technology, initially from a hydraulic engineering and water management perspective, and evaluated from a geotechnical perspective by the Institute of Geotechnical Engineering and Construction Operations. The Institute for Geo-Hydroinformatics analyzes the effects with regard to groundwater levels and possible salinization of the groundwater. Subsequently, the ecological and economic analyses and evaluations are carried out. At the end there should be concrete options for action. The tools, methods and evaluation schemes developed are to be prepared in such a way that they can also be applied to other German estuaries such as the Weser.
Sea levels are rising
Without sufficient protection by dikes, walls and flood plains as well as barrages and drainage structures, storms and floods would cause enormous damage. This has been painfully demonstrated time and again in the past. "As a result of climate change and the associated rise in sea level, storm surges will accumulate much higher in the future for the same storm intensity. Water levels that used to occur on average once every hundred years will then also come upon us much more frequently, for example every five years. In addition, storms may become even more intense as a result of climate change, which would then further increase the extreme water levels," says Fröhle, the institute's director. The TideelbeKlima project therefore wants to define protection lines to form safe zones that can withstand higher mean water levels and more frequent floods. In addition to dikes and flood protection walls, there are a variety of concepts to protect against flooding. These range from adapted construction methods and the creation of more space for water to dams or barrages that can prevent a flood wave from entering.
Raising dikes, reinforcing protective walls
Just a few decades ago, experts assumed that the average sea level would rise by 25 centimeters in a hundred years. Climate change is having an accelerating effect, so that sea levels are now expected to continue to rise by one meter per century. Every ten years, planned flood protection targets and measures are re-evaluated so that protection measures can be adapted if necessary. In the current construction program for the Hanseatic City of Hamburg, for example, it is planned to expand dikes and flood protection facilities to a height of at least 8.30 meters above sea level.
One measure is to keep water out, another is to give it more room to flood. Especially on the coasts, such polders can serve as retention areas to prevent water from causing further destruction. "Ultimately, flood protection can even go as far as dredging areas that have already been diked. In the area of the Tidal Elbe, however, the effectiveness of such measures from a hydraulic engineering point of view is comparatively low," explains TU scientist Fröhle. Quite the opposite is true of the extremely costly but effective measure of erecting a barrage. This has already been done for the neighboring smaller Elbe tributaries, such as the Este or the Krückau, and the Eider, which flows into the North Sea. If such a structure were built on the Elbe, however, it would be several kilometers long and much larger and longer than the existing barrages. Its construction would cost billions of euros. The advantage would be that storm surges could be kept out of the Elbe and damage avoided from the outset.
In addition to the Institute of River and Coastal Engineering at TU Hamburg as coordinator, the TideelbeKlima project also involves the TUHH-Institutes of Institute of Geotechnical Engineering and Construction Management and Geo-Hydroinformatics and the Institute of Geoecology at the TU Braunschweig and the Institute for Ecological Economy Research (IÖW) in Berlin.
