Biodegradable Geotextiles for Natural Bank Protection

Stable bank protection is essential for the protection of waterways, but traditional methods such as rockfill are considered to be less than natural. Fraunhofer UMSICHT has now teamed up with partners to develop a geotextile that is both biodegradable and technically resilient. The combination of PLA and natural fibers combines ecological compatibility with functionality.

In this interview, project manager Pia Borelbach explains how the material works, why it is suitable for widespread use, and in which applications it has potential beyond hydraulic engineering.

What are the special material properties of the geotextile you have developed?

Pia Borelbach: The geotextile we have developed has specific material properties that ensure both ecological compatibility and technical resilience. The banks of waterways are subject to high hydraulic loads, especially from shipping. Our geotextile meets the minimum mechanical requirements specified by the BAW, effectively retains the soil and at the same time remains sufficiently permeable to prevent excess water pressure under the geotextile. These properties were successfully demonstrated over a period of three years in a field trial on the BAW test track on the Rhine.

The geotextile fleece consists of a combination of polylactic acid fibers (PLA) and natural fibers. The PLA fibers ensure long-lasting stability, while the natural fibers degrade more quickly and release root channels to ensure good root penetration. It is also designed to biodegrade completely in the soil over the long term. Samples taken after three years on the Rhine showed the PLA fibers beginning to degrade. In further sampling after five and ten years, we will continue to monitor biodegradability under waterway conditions even after the end of the project. Although root penetration was possible with willow mulch, the geotextile impaired root and shoot formation. Therefore, in 2024, an optimized geotextile was installed at another location on the test section under willow spreader mats and seed mats. We do not yet have any test results for this.

Which industrial manufacturing processes are suitable for the production of geotextiles – and how realistic is scaling up for widespread use?

Borelbach: For geotextiles, there are generally different manufacturing processes for nonwovens, woven fabrics, and others, depending on the requirements for the textiles. Due to the required filter effect, high weight per unit area, and combination of PLA and natural fibers, Bioshoreline geotextiles were manufactured as carded nonwovens, which were mechanically bonded using needles. The PLA staple fibers used are already part of the product range of project partner Indorama Ventures Fibers Germany GmbH, and the natural fibers used are also available on the market. The nonwovens were manufactured at project partner BNB Brinkman GmbH & Co. KG on an industrial plant. There are therefore no obstacles to scaling up for widespread use, either in terms of raw materials or manufacturing technology.

What specific sustainability advantages do geotextiles offer compared to traditional bank protection systems?

Borelbach: Traditional bank protection for waterways is technical revetment, i.e., stones or concrete, due to the hydraulic load. Geotextiles enable a more natural design of waterway banks through the integration of vegetation, which promotes the creation of diverse habitats for plants and animals typical of banks, thus increasing biodiversity. In addition, biodegradable geotextiles are more environmentally friendly because they decompose in the soil after their useful life and, unlike conventional plastic geotextiles, do not leave any permanent residues. Greened banks also contribute to long-term improvements in water quality by effectively binding and absorbing pollutants and nutrients, reducing the risk of eutrophication and supporting a healthier aquatic ecosystem.

Which industries and applications beyond bank construction could also benefit from the use of biodegradable geotextiles?

Borelbach: Biodegradable geotextiles offer a wide range of applications beyond bank construction. They are particularly useful where temporary stabilization is required and a permanent installation would not be practical or environmentally friendly. This could be, for example, slope stabilization, where planting later takes over the erosion control function. Or temporary construction roads, especially for projects such as the construction of wind turbines. These roads often run across agricultural land and are only needed for the duration of the construction project. Once the project is complete, the degradable materials allow the soil to be easily returned to its original use without causing permanent environmental damage. Biodegradable geotextiles could also play an important role in environmental and renaturation projects in the future.