Under a lahnung one understands a Uferschutzanlage. These are usually double rows of wooden piles, which are built with interlaced shrubs, so-called fascines, in the shore area into the sea. Depending on the depth, current and background, gabions are also successfully used here. The approximately 60-80 cm high Lahnungen enclose fields of approximately 100 x 200 m size.
In Germany, Lahnungen are often built in the shores of the Wadden Sea. The resulting warning fields are dehydrated by ditches, so-called trunks or truffles. These are up to 2 m wide, a few decimeters deep and divide a Lahnungsfeld in up to 10 m wide beds. The Grüppen are dug linear and usually run perpendicular to the coast. The excavated soil is thrown laterally on the Lahnungsfelder. At high tide, the water flows to these fields, where it comes to rest and the entrained suspended matter can settle. This promotes sedimentation and silting up.
If the fields are sufficiently overgrown, the trenches are further dredged, using the excavation to further increase the mudflats between the trunks. At the same time it also improves the drainage of the soil between the trenches. Soil elevations are up to 10 cm per year, after one to two decades salt marshes have emerged from the seabed with a foreland level above the normal flood level.
The use of Lahnungen for the purpose of land reclamation often takes place in three stages. In front of a dike pond, a first felling field is built in which sediments are deposited. After a few years, a second field will be built on the seafront before the first. Once again, sediments deposit there, while pioneer plants emerge in the first field. Finally, a third Lahnungfeld is set up, while the second is now overgrown by Pionierpflanzen and have become from the first already salt marshes of the dyke foreland.
This type of coastal protection not only reclaims land, but also makes the hinterland safer, because in storm surges, the force of the waves against the dikes is weakened.
Source: Wikipedia