The banks of inland waterways are exposed to a variety of stresses, including the waves caused by shipping. To prevent erosion, these are usually technically secured by riprap or stone walls, which, however, can have a negative impact on the ecosystems. In the “Bioshoreline” joint research project – funded by the Federal Ministry of Food and Agriculture – researchers led by the Fraunhofer UMSICHT developed a biodegradable geotextile made from renewable raw materials that is to serve as a temporary filter for bank protection on inland waterways.

Stable and biodegradable at the same time

The aim of the project was to develop a geotextile filter for biological bank stabilization systems. This filter is designed to stabilize the soil in front of the bank reinforcement with plants and then completely degrade as soon as the plant roots can take over this task. The novel geotextile consists of a mixture of rapidly degradable natural fibers and bio-based, slowly degradable synthetic fibers. This combination is designed to provide the necessary stability for at least three years – while also being fully biodegradable. “One of the challenges of the project was to develop a stable geotextile that also allows plant roots to grow through and that completely degrades after a certain period of time. After many optimization steps, we have now succeeded in producing a suitable prototype,” explains project manager Pia Borelbach of Fraunhofer UMSICHT.

First prototypes in use

In January 2020, the first prototypes were installed on a test section on the Rhine near Worms. The general rootability of the geotextile filters produced was demonstrated with willow spreading layers as planting material, both in special test boxes and in the field. Samples were taken and tested after one, two and three years. The results showed that degradation processes had begun. Based on the findings from field and rooting experiments, the researchers further optimized the geotextile to further improve rooting. This prototype has now been in use under stone mattresses since March 2023 and under wicker matting and seed mats on the test track since April 2024. The project is expected to open up new possibilities for nature-based flood protection while also creating a new field of application for bio-based and biodegradable plastics.

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