Terrafix and willow bundles stabilise groynes

Terrafix and willow bundles stabilise groynes

Cuxhaven, Germany | NAUE GmbH & Co. KG

Between Cuxhaven and Otterndorf is an area called „Altenbrucher Bogen (Bend)“. There, the Elbe River curves and the navigable water extends far from the shore. The strong currents in this area have caused continuous erosion to the shore, threatening the shore dike. Furthering plans have been set in motion to deepen the navigable water to enable easy passage for large container ships regardless of the tide. The solution has been found through highly engineered, modern geotextiles and traditional fascines.

Above the water line, the groynes appear to be the same as traditional stone breakwaters. The special characteristics that define these groynes are hidden underwater: Large geosynthetic revetment mats, in combination with wood fascines, not only prevent tidal erosion but promote sand deposition.

Each of the special mats are assembled on site and measure 30 m x 70 m. Terrafix® geotextile rolls are unrolled next to one another at the shore and sewn together. Terrafix® 773 G43, a multilayer nonwoven geotextile, has been selected for its performance and durability in coastline erosion prevention applications.This  Terrafix® is needle-punched to a layer equipped with loops. Ropes, which tightly bind the woody fascines to the geotextile, are pulled through the loops. The fascines consist of numerous willow rods bound into long round bundles several metres long. The fascines are fastened to Terrafix® at a right angle, lengthwise and crosswise, about 1 m apart.

Tugboats, then, pull the fascine mattresses into position. Small rocks weight them as they are lowered. Next, the actual groynes are built up using larger breakwater stone.

Cuxhaven, Germany | NAUE GmbH & Co. KG

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The groynes and fascine mattresses now provide mutual protection. The rocks hold the mattresses in place. The nonwoven prevents erosion of the waterway bed. The fascine pattern promotes sedimentation. This creates shallow water areas with sand deposits between the groynes.

The project in total covers an area of over 220,000 m² of Terrafix® geotextile productsand is considered one of the largest water construction zones in Germany.