Bioshoreline: Biodegradable geotextiles for bank protection

The aim of the “Bioshoreline“ research project is to develop a biodegradable geotextile from renewable raw materials for use as a temporary filter for technical and biological bank protection on inland waterways, i.e. for environmentally friendly bank protection using plants. The innovative geotextile filter should initially retain the soil in the bank area until the plant roots have grown sufficiently and are able to take over the filter function. The geotextile filter will gradually degrade completely in parallel with this. To achieve this, the project team BNP Brinkmann GmbH & Co. KG, Inorama Ventures Fibers Germany GmbH (formerly Trevira GmbH), FKuR Kunststoff GmbH, Bundesanstalt für Wasserbau (BAW), and Fraunhofer UMSICHT are combining a mixture of rapidly degradable natural fibers and bio-based, slowly degradable synthetic fibers in a geotextile fleece and are testing the technical properties and biodegradability in particular. With this development, the project team is opening up a new field of application for bio-based and biodegradable plastics.

Shipping traffic in inland waterways leads to changing hydraulic loads on the banks. With the introduction of the European Water Framework Directive (WFD), the banks, which have so far been mainly secured using technical methods, are to be made more natural over the long term by using plants. 

For the initial state, additional fortifications and measures are usually required to ensure the safety of the banks until sufficient roots have formed. This also includes temporary geotextile fleeces, which guarantee filter stability in the bank area for the first three years after installation. These must retain the soil and have sufficient permeability and strength while also being permeable to roots and biodegradable over the long term so as not to permanently restrict the passage of microorganisms in the bank area. Once suitable filter fleeces are available, the applicability of more natural bank protection measures on inland waterways can be increased.

Geotextile filter closes research gap

Biodegradable nonwovens tested to date for technical and biological bank protection are not sufficiently stable under the given loads and degrade too quickly. Alternatives made from plastic are stable and durable but remain permanently in the soil. A suitable solution that meets all of the requirements is still lacking.

With the development of a biodegradable geotextile filter made from renewable raw materials, the partners in the “Bioshoreline“ project are closing this gap. This is because the innovative filter enables plants to grow in technical and biological bank protection systems and it gradually breaks down completely so that the vegetation can take over the filter stability in the bank. The geotextile filter is composed of various rapidly degradable natural fibers and slowly degradable industrially-created fibers, whereby the technical requirements are met for at least three years.

The first prototypes of geotextile filters have been produced and characterized so far. Suitable raw materials were selected first of all. The processing properties and the biodegradability of the synthetic fibers had to be adapted and the processing conditions for the production of the polymers had to be developed. To select suitable fibers for the prototypes, the processing properties of geotextiles were investigated in addition to the various compositions and the different degradation times associated with them.

The general rootability of the geotextile filters produced was demonstrated by the BAW using willow spread layers as planting material both in special test boxes and in the field on the test section on the Rhine. Fewer and shorter roots and shoots were found in the plantings with geotextile compared to those without geotextile. However, as the rootability is likely to improve continuously as the geotextile degrades, the lower root penetration observed is considered sufficient for the intended purpose.

In January 2020, the various prototypes were installed on the BAW test section on the Rhine near Worms on a 30 m x 6 m embankment section under stone mattresses. Changing water levels can be used to determine the biodegradation under different hydraulic loads. Samples were taken and tested after one, two and three years respectively. This showed that between installation in 2020 and 2022, the tensile strength and tamp force of the geotextile and the molar mass of the PLA fibers used only changed within the range of the measured values. The samples taken in 2023, on the other hand, show a significant reduction in these characteristic values. The limit values for tensile strength required for the condition three years after installation are already slightly undercut in some cases. The changes show that degradation processes have begun.

Further optimization of the geotextile was carried out on the basis of the knowledge gained from field and root penetration tests. The aim of this optimization was to improve root penetration. The optimized geotextile has been tested under stone mattresses since March 2023 and under willow chaff and seed mats on the test track since April 2024.

• BNP Brinkmann GmbH & Co. KG
• Inorama Ventures Fibers Germany GmbH (formerly Trevira GmbH)
• FKuR Kunststoff GmbH
• BAW Bundesanstalt für Wasserbau