Results of the RFBR project 18-55-76002 in 2018

The widespread use of geosynthetic materials in hydraulic engineering is due to the enormous economic effect. It is considered that geosynthetic materials, if properly treated with antioxidants, will serve in underwater structures for at least 100 years (under conditions of limited access of oxygen and low temperatures). However, the effects of sea, sun, wind and people affect geosynthetics, which is used in shore protection. And it collapses. This can become sources of a new type of pollutant – residues (debris) of geotextile materials, which later turn into microparticles (known as microplastic) that are dangerous to the environment.

In the course of research in 2018, information on the parameters of 13 coastal defenses on the coast of the Kaliningrad Oblast (Russian territory in the South-Eastern Baltic), in which geosynthetic materials are used, was obtained and verified. These structures were built over the past 10 years and protect 7 km of the coast. The analysis of the length of the protected coast with the use of geosynthetic materials and the timing of its operation in an aggressive coastal-marine environment was carried out in the project. It was found that in practice such facilities are potential sources of contamination with various synthetic elements.

Monitoring of the beaches of the South-Eastern Baltic showed that fragments of geosynthetic materials from the coastal and engineering structures are unevenly distributed. Several methods of searching for fragments of geosynthetic materials have been tested, as a result of which a method of “Continuous visual scanning” has been developed. This technique allows to objectively assess the degree of pollution of beaches with geosynthetic materials. It was revealed that the greatest visible effect in the pollution of beaches is made by the remnants of woven textiles (big bags / bags), actively breaking up into fibers. These fibers migrate along the coast, settling on the beach and at the bottom. Fragments of nonwoven geotextiles (such as dornit) from the protective berms / blind area enter the marine environment in large quantities.

Method of “Continuous visual scanning”
Field board

29 expedition exits (during June – November 2018) were conducted to survey the state of pollution of the coastal strip of the Kaliningrad Oblast. The entire coast (135 km) of the Vistula and Curonian Spit, the western and northern coasts of the Sambian Peninsula were surveyed by using the “Continuous visual scanning” methodic. The remains of geosynthetic materials used in the shore protection structures (dornit, geogrids, geo cells, gabion braids), as well as other materials (Big bags, colored rods, car tires, fishing nets, ropes / ropes) were found.

Table 1. Examples of the state of different types of geosynthetic materials

Type New /
non- worn out
Worn out High worn out
Dornit
Dornit
Gabion braid
Big-Bag

The dimensions of the remnants of geosynthetic materials, that were found on the beach and in the riparian strip of the shores of the Kaliningrad Oblast, vary from a few centimeters to several meters.

The dimensions of the remnants of geosynthetic materials vary from a few centimeters…
… to several meters

The primary analysis of the data obtained showed strong contamination with residues of geosynthetic material and other large debris on the northern coast of the Sambian Peninsula and on the Curonian Spit. Similar pollution on the western coast of the Sambian Peninsula and on the Vistula Spit is practically not found, which correlates with the location of the main engineering structures.

A separate project task is to simulate the behavior of residual geosynthetic materials. It can be implemented using algorithms already implemented by the SHYFEM model. Numerical simulation (with emphasis on the parameterization of the transport of particles of geosynthetic materials) will be based on field data taking into account the typical types of pollutants and their sources. Gabion braids (almost neutral buoyancy) and dornit pieces (sand-rich material heavier than water) will be used as test impurities.

Analysis of the results of surveys of the coastal strip of the Kaliningrad Oblast showed that the bulk of the remnants of geosynthetic materials were found within a radius of 2-5 km from the expected sources, but mostly east of them. This characterizes the existing spacing of these pollutants, which began to appear in the coastal zone after 2010. The most common pollutant can be called the remnants of a sheath from gabions, and their distribution range extends to the Lithuanian border on the Curonian Spit.

Storm episodes and long periods of wind-wave load on the coast lead to active migration of fragments of geosynthetic materials. It is likely that part of the geosynthetic material settles on the coastal slope, and during the storm it migrates with algae and other sedimentary material, is carried to the beach, and can also return to the sea again, undergoing a mechanical impact from the sedimentary material. Fragments of geosynthetics can be transported over fairly long distances by currents.

The greatest visible effect in the pollution of the beaches is made by the remnants of woven textiles that actively break down into fibers. Its migrate along the coast, settling on the beach and at the bottom, pollute the entire coastline, staying deep in the beach or intermingling with algae and other debris. Thus, a known geosynthetic material from a certain source can serve as a tracer for determining the transfer of material by currents.