Free passage at low water: this is how the Rhine is to be "rebuilt"

In the summer of 2018, the German economic artery dries up: the Rhine carries so little water that many cargo ships have to stay in port. So that this doesn't happen again, the Federal Institute for Hydraulic Engineering has rebuilt a section in a huge model and is planning "adjustments".

Basel, Ludwigshafen, Mainz, Koblenz, Bonn, Cologne, Düsseldorf, Duisburg, Rotterdam – one important business location follows the next on the Rhine. Around 60 million people live in the catchment area of ​​Europe's most important waterway. Almost 200,000 ships are on the move every year on the Lower Rhine in North Rhine-Westphalia alone, which is an average of around 550 per day.

But in the summer of 2018, the German and European economic arteries suddenly dry up: It hasn't rained for months, the level sinks so much that many cargo ships can only be partially loaded with goods and some cannot be loaded at all, because otherwise they would run aground . This exceptional case could become the norm in the second half of the century due to climate change, says Christoph Heinzelmann in the ntv podcast "Another thing learned". The civil engineer has been head of the Federal Institute for Hydraulic Engineering (BAW) for 15 years. He and his team are currently working as an appraiser on one of the most important construction projects in German waterways, the "optimization of the unloading of the fairways on the Middle Rhine", as it is called in the federal traffic route plan. So they think about what can be done so that even when the water is low, no cargo ship has to stay in the Rhenish port in the future.

A 50-kilometer section between Mainz and St. Goar, a small town on the western bank of the Middle Rhine in Rhineland-Palatinate, is particularly tricky. When the tide is low, the fairway is only 1.90 meters deep in six places – and therefore 20 centimeters too low for most cargo ships. With "river engineering measures", space is to be created under the keel at these junction points.

Christoph Heinzelmann and his team are investigating which ones are suitable and how exactly they should be implemented. In four cases, they can test their ideas and approaches on the computer. At these points it is sufficient to prevent landings of sand and gravel so that ships can continue to sail even when the water is low. But in the area of ​​the so-called Jungferngrund, near the famous Loreley, the Rhine meanders through the Rhenish slate mountains. The conditions there are so complex that computer models are not safe and accurate enough. At these points the bottom is interspersed with rocks, and the river makes a 90-degree curve. For a 4.4 kilometer long section, an objective model on a 1:60 scale was built in Karlsruhe, says BAW boss Heinzelmann.

Dry feet on the river bed

The replica of the Rhine is a dream for every model maker. On a total area of ​​410 square meters, every bend and depression resembles the original. Every crag can be found where it is in the real Rhine. The construction alone took more than a year. "We went on the Rhine with the so-called diving bell ship," explains the civil engineer, explaining the data acquisition. "This bell is placed under positive pressure and on the river bed. Then you can walk on the bed of the Rhine with dry feet and determine exactly how the bed surface is composed."

This knowledge is important in order to be able to precisely represent the various deposits and obstacles on the Jungferngrund and to find out how they are influenced by the current. A grain of sand, for example, weighs much less than a pebble or stone. But that cannot be reduced to a scale of 1:60, says Christoph Heinzelmann, because then it is no longer a grain of sand and loses its soil mechanical properties. "In the model, we therefore work with three representatives who neatly map the material on the Rhine bed, from sand to gravel to stones."

These representatives are plastic granules. This varies in weight so that the artificial sand and the artificial gravel behave the same way in the model as in the real Rhine. They are colored in different colors so that the hydraulic engineering experts can recognize which rock is affected by the various measures and how, and where problems arise.

Competition of the river models

Soil extraction and the prevention of landings are not enough at the two bottlenecks on the Jungferngrund to enable cargo ships to move freely even at low tide. A combination is necessary, says BAW boss Heinzelmann. The water level had to be raised during low water events, and some rock peaks had to be removed or milled off. The civil engineer says that the consequences for the environment are being dealt with intensively. And which process is the gentlest.

It will be a few years before the planning approval decision is final and there is building permission. For the "unloading optimization of the fairways on the Middle Rhine", the reports with the planning instructions for the responsible waterways and shipping authority for the Rhine have only just been completed. These later form the basis for the planning approval procedure.

At least until that is done, the huge model of the Rhine will also remain. That will only be torn down when all questions have been answered, says the BAW boss. Hopefully it won't take too long, even if there's a lot of work involved. On the one hand, because the German economy is pushing for the project to be implemented quickly. On the other hand, because space is scarce in Karlsruhe. "We not only have the Rhine in the hall, but also the Lahn, a piece of the Elbe, the Neckar or the Danube with a large model," says Christoph Heinzelmann, explaining the unusual problem. "The models compete with each other."

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