Geotextile materials are increasingly being used in coastal protection as an alternative to natural stone, slag and concrete. In this environment, geotextiles, like all technical surfaces, are colonised by organisms, a phenomenon commonly referred to as biofouling. In a two-year experiment, the colonisation of benthic organisms on two different geotextile materials (woven and non-woven) was investigated in the Elbe estuary near Cuxhaven and compared with colonisation on unglazed ceramic tiles as a reference. The most important finding was that the non-woven fabric was colonised by significantly fewer species, fewer individuals and lower biomass values than the woven fabric and ceramic tiles. No such large difference was found between woven fabric and ceramic tiles. The number of species and the number of individuals did not show any significant increases over time between the first and second years, while the biomass on all materials still increased significantly. However, the biomass of the fouling organisms was almost two orders of magnitude smaller on geotextiles made of non-woven fabrics than on the woven material. Exposure to seawater had no adverse effect on the stability of the geotextiles (results of a tensile test). Geotextile materials therefore offer a unique choice for engineers in coastal and hydraulic engineering: depending on the application, they can choose between a material that can be easily colonised by benthic species or a material that minimises this colonisation.

Literature

Markus A. Wetzel, Jörg Scholle, Katharina Teschke (2014). Artificial structures in sediment-dominated estuaries and their possible influences on the ecosystem. Marine Environmental Research, Volume 99, Pages 125-135. (https://epic.awi.de/id/eprint/36043/1/Wetzel_et_al2014.pdf)

Markus A. Wetzel, Melanie Wiegmann, Jochen H.E. Koop (2011). The ecological potential of geotextiles in hydraulic engineering, Geotextiles and Geomembranes, Volume 29, Issue 4, Pages 440-446.

Fig. 1: The experimental rack recovered from the deck of the MS Vogelsand after one year of exposure in the Elbe estuary

Fig. 2: Result after one year: no encrusting species (barnacles) on the nonwoven fabric material

This article was first published in 2019 at the Naue Colloquium.

Geotechnical classification

Coastal protection and hydraulic structures in tidal estuaries, where geotextile cover layers are used as an alternative to armourstone, slag or concrete elements.
Nonwoven and woven geotextiles acting as artificial hard substrates that are colonised by benthic organisms (biofouling), thereby influencing surface roughness, flow conditions and ecological functionality.
Field investigations in the Elbe estuary comparing colonisation behaviour on different geotextile materials with unglazed ceramic tiles as reference surfaces over a multi-year exposure period.
Markedly lower species richness, individual numbers and biomass on nonwoven geotextiles compared to woven fabrics and ceramic tiles, while biomass on all substrates continues to increase over time.
Long-term exposure to seawater without detectable loss of tensile strength, so geotextile type, surface structure and pore space can be used deliberately as design parameters for ecological and hydraulic performance.

Typical project questions

How does biofouling on geotextile cover layers affect hydraulic roughness, erosion resistance and the service life of coastal and hydraulic engineering structures?
Which geotextile type (nonwoven vs. woven, surface structuring) is appropriate when the project goal is either to minimise biofouling or to promote targeted ecological enhancement of artificial structures?
How can geotextile filter and protective layers be dimensioned and verified to ensure long-term mechanical stability under seawater exposure, currents and biological colonisation?

Suitable Naue products & system solutions

A project-specific system selection enables protective structures to be implemented efficiently, durably, and tailored to local conditions.

Geotextile cover layers in coastal protection

Secutex® nonwoven geotextile as a filter and protective cover layer on sand and fine-grained embankments; the nonwoven structure and pore space allow targeted control of colonisation behaviour and resulting hydraulic roughness.
Woven geotextiles as alternative cover layers when a pronounced surface structure and higher colonisation density are desired to create biologically active hard-substrate conditions in the tidal zone.

Filter and separation beneath hydraulic revetments

Secutex® nonwoven geotextile as a filter and separation layer between subsoil and revetment (rock armour, precast concrete elements or geotextile sand containers), designed to prevent internal erosion even with biofilm and growth on the surface.
Secudrain® drainage mats as combined filter and drainage layers behind cladding, seawalls or sheet piles, reducing pore water pressures and limiting fine soil washout through an integrated geotextile filter.

Erosion control and ecological integration of shorelines

Secumat® erosion control systems to stabilise embankment and shoreline surfaces subject to wave attack and currents; open or vegetated surface configurations enable hydraulic stability and ecological integration of the structure.
Combinations of Secutex® nonwoven geotextile filter layers with Secumat® erosion control systems or mineral revetments to secure long-term filter function and mechanical integrity under seawater and biofouling influence.

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The ecological potential of geotextiles